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1228 lines
42 KiB
1228 lines
42 KiB
//===- FunctionAttrs.cpp - Pass which marks functions attributes ----------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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///
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/// \file
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/// This file implements interprocedural passes which walk the
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/// call-graph deducing and/or propagating function attributes.
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///
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/IPO/FunctionAttrs.h"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/ADT/SCCIterator.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/StringSwitch.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/BasicAliasAnalysis.h"
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#include "llvm/Analysis/CallGraph.h"
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#include "llvm/Analysis/CallGraphSCCPass.h"
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#include "llvm/Analysis/CaptureTracking.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/InstIterator.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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using namespace llvm;
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#define DEBUG_TYPE "functionattrs"
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STATISTIC(NumReadNone, "Number of functions marked readnone");
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STATISTIC(NumReadOnly, "Number of functions marked readonly");
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STATISTIC(NumNoCapture, "Number of arguments marked nocapture");
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STATISTIC(NumReadNoneArg, "Number of arguments marked readnone");
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STATISTIC(NumReadOnlyArg, "Number of arguments marked readonly");
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STATISTIC(NumNoAlias, "Number of function returns marked noalias");
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STATISTIC(NumNonNullReturn, "Number of function returns marked nonnull");
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STATISTIC(NumNoRecurse, "Number of functions marked as norecurse");
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namespace {
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typedef SmallSetVector<Function *, 8> SCCNodeSet;
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}
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namespace {
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/// The three kinds of memory access relevant to 'readonly' and
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/// 'readnone' attributes.
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enum MemoryAccessKind {
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MAK_ReadNone = 0,
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MAK_ReadOnly = 1,
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MAK_MayWrite = 2
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};
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}
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static MemoryAccessKind checkFunctionMemoryAccess(Function &F, AAResults &AAR,
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const SCCNodeSet &SCCNodes) {
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FunctionModRefBehavior MRB = AAR.getModRefBehavior(&F);
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if (MRB == FMRB_DoesNotAccessMemory)
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// Already perfect!
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return MAK_ReadNone;
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// Non-exact function definitions may not be selected at link time, and an
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// alternative version that writes to memory may be selected. See the comment
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// on GlobalValue::isDefinitionExact for more details.
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if (!F.hasExactDefinition()) {
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if (AliasAnalysis::onlyReadsMemory(MRB))
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return MAK_ReadOnly;
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// Conservatively assume it writes to memory.
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return MAK_MayWrite;
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}
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// Scan the function body for instructions that may read or write memory.
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bool ReadsMemory = false;
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for (inst_iterator II = inst_begin(F), E = inst_end(F); II != E; ++II) {
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Instruction *I = &*II;
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// Some instructions can be ignored even if they read or write memory.
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// Detect these now, skipping to the next instruction if one is found.
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CallSite CS(cast<Value>(I));
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if (CS) {
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// Ignore calls to functions in the same SCC, as long as the call sites
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// don't have operand bundles. Calls with operand bundles are allowed to
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// have memory effects not described by the memory effects of the call
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// target.
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if (!CS.hasOperandBundles() && CS.getCalledFunction() &&
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SCCNodes.count(CS.getCalledFunction()))
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continue;
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FunctionModRefBehavior MRB = AAR.getModRefBehavior(CS);
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// If the call doesn't access memory, we're done.
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if (!(MRB & MRI_ModRef))
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continue;
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if (!AliasAnalysis::onlyAccessesArgPointees(MRB)) {
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// The call could access any memory. If that includes writes, give up.
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if (MRB & MRI_Mod)
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return MAK_MayWrite;
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// If it reads, note it.
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if (MRB & MRI_Ref)
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ReadsMemory = true;
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continue;
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}
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// Check whether all pointer arguments point to local memory, and
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// ignore calls that only access local memory.
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for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
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CI != CE; ++CI) {
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Value *Arg = *CI;
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if (!Arg->getType()->isPtrOrPtrVectorTy())
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continue;
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AAMDNodes AAInfo;
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I->getAAMetadata(AAInfo);
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MemoryLocation Loc(Arg, MemoryLocation::UnknownSize, AAInfo);
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// Skip accesses to local or constant memory as they don't impact the
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// externally visible mod/ref behavior.
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if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
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continue;
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if (MRB & MRI_Mod)
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// Writes non-local memory. Give up.
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return MAK_MayWrite;
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if (MRB & MRI_Ref)
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// Ok, it reads non-local memory.
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ReadsMemory = true;
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}
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continue;
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} else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
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// Ignore non-volatile loads from local memory. (Atomic is okay here.)
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if (!LI->isVolatile()) {
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MemoryLocation Loc = MemoryLocation::get(LI);
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if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
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continue;
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}
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} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
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// Ignore non-volatile stores to local memory. (Atomic is okay here.)
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if (!SI->isVolatile()) {
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MemoryLocation Loc = MemoryLocation::get(SI);
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if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
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continue;
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}
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} else if (VAArgInst *VI = dyn_cast<VAArgInst>(I)) {
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// Ignore vaargs on local memory.
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MemoryLocation Loc = MemoryLocation::get(VI);
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if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
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continue;
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}
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// Any remaining instructions need to be taken seriously! Check if they
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// read or write memory.
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if (I->mayWriteToMemory())
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// Writes memory. Just give up.
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return MAK_MayWrite;
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// If this instruction may read memory, remember that.
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ReadsMemory |= I->mayReadFromMemory();
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}
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return ReadsMemory ? MAK_ReadOnly : MAK_ReadNone;
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}
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/// Deduce readonly/readnone attributes for the SCC.
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template <typename AARGetterT>
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static bool addReadAttrs(const SCCNodeSet &SCCNodes, AARGetterT AARGetter) {
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// Check if any of the functions in the SCC read or write memory. If they
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// write memory then they can't be marked readnone or readonly.
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bool ReadsMemory = false;
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for (Function *F : SCCNodes) {
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// Call the callable parameter to look up AA results for this function.
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AAResults &AAR = AARGetter(*F);
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switch (checkFunctionMemoryAccess(*F, AAR, SCCNodes)) {
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case MAK_MayWrite:
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return false;
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case MAK_ReadOnly:
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ReadsMemory = true;
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break;
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case MAK_ReadNone:
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// Nothing to do!
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break;
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}
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}
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// Success! Functions in this SCC do not access memory, or only read memory.
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// Give them the appropriate attribute.
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bool MadeChange = false;
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for (Function *F : SCCNodes) {
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if (F->doesNotAccessMemory())
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// Already perfect!
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continue;
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if (F->onlyReadsMemory() && ReadsMemory)
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// No change.
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continue;
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MadeChange = true;
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// Clear out any existing attributes.
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AttrBuilder B;
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B.addAttribute(Attribute::ReadOnly).addAttribute(Attribute::ReadNone);
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F->removeAttributes(
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AttributeSet::FunctionIndex,
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AttributeSet::get(F->getContext(), AttributeSet::FunctionIndex, B));
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// Add in the new attribute.
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F->addAttribute(AttributeSet::FunctionIndex,
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ReadsMemory ? Attribute::ReadOnly : Attribute::ReadNone);
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if (ReadsMemory)
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++NumReadOnly;
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else
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++NumReadNone;
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}
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return MadeChange;
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}
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namespace {
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/// For a given pointer Argument, this retains a list of Arguments of functions
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/// in the same SCC that the pointer data flows into. We use this to build an
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/// SCC of the arguments.
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struct ArgumentGraphNode {
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Argument *Definition;
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SmallVector<ArgumentGraphNode *, 4> Uses;
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};
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class ArgumentGraph {
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// We store pointers to ArgumentGraphNode objects, so it's important that
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// that they not move around upon insert.
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typedef std::map<Argument *, ArgumentGraphNode> ArgumentMapTy;
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ArgumentMapTy ArgumentMap;
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// There is no root node for the argument graph, in fact:
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// void f(int *x, int *y) { if (...) f(x, y); }
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// is an example where the graph is disconnected. The SCCIterator requires a
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// single entry point, so we maintain a fake ("synthetic") root node that
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// uses every node. Because the graph is directed and nothing points into
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// the root, it will not participate in any SCCs (except for its own).
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ArgumentGraphNode SyntheticRoot;
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public:
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ArgumentGraph() { SyntheticRoot.Definition = nullptr; }
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typedef SmallVectorImpl<ArgumentGraphNode *>::iterator iterator;
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iterator begin() { return SyntheticRoot.Uses.begin(); }
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iterator end() { return SyntheticRoot.Uses.end(); }
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ArgumentGraphNode *getEntryNode() { return &SyntheticRoot; }
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ArgumentGraphNode *operator[](Argument *A) {
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ArgumentGraphNode &Node = ArgumentMap[A];
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Node.Definition = A;
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SyntheticRoot.Uses.push_back(&Node);
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return &Node;
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}
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};
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/// This tracker checks whether callees are in the SCC, and if so it does not
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/// consider that a capture, instead adding it to the "Uses" list and
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/// continuing with the analysis.
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struct ArgumentUsesTracker : public CaptureTracker {
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ArgumentUsesTracker(const SCCNodeSet &SCCNodes)
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: Captured(false), SCCNodes(SCCNodes) {}
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void tooManyUses() override { Captured = true; }
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bool captured(const Use *U) override {
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CallSite CS(U->getUser());
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if (!CS.getInstruction()) {
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Captured = true;
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return true;
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}
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Function *F = CS.getCalledFunction();
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if (!F || !F->hasExactDefinition() || !SCCNodes.count(F)) {
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Captured = true;
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return true;
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}
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// Note: the callee and the two successor blocks *follow* the argument
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// operands. This means there is no need to adjust UseIndex to account for
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// these.
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unsigned UseIndex =
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std::distance(const_cast<const Use *>(CS.arg_begin()), U);
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assert(UseIndex < CS.data_operands_size() &&
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"Indirect function calls should have been filtered above!");
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if (UseIndex >= CS.getNumArgOperands()) {
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// Data operand, but not a argument operand -- must be a bundle operand
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assert(CS.hasOperandBundles() && "Must be!");
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// CaptureTracking told us that we're being captured by an operand bundle
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// use. In this case it does not matter if the callee is within our SCC
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// or not -- we've been captured in some unknown way, and we have to be
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// conservative.
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Captured = true;
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return true;
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}
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if (UseIndex >= F->arg_size()) {
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assert(F->isVarArg() && "More params than args in non-varargs call");
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Captured = true;
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return true;
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}
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Uses.push_back(&*std::next(F->arg_begin(), UseIndex));
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return false;
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}
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bool Captured; // True only if certainly captured (used outside our SCC).
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SmallVector<Argument *, 4> Uses; // Uses within our SCC.
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const SCCNodeSet &SCCNodes;
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};
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}
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namespace llvm {
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template <> struct GraphTraits<ArgumentGraphNode *> {
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typedef ArgumentGraphNode NodeType;
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typedef SmallVectorImpl<ArgumentGraphNode *>::iterator ChildIteratorType;
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static inline NodeType *getEntryNode(NodeType *A) { return A; }
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static inline ChildIteratorType child_begin(NodeType *N) {
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return N->Uses.begin();
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}
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static inline ChildIteratorType child_end(NodeType *N) {
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return N->Uses.end();
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}
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};
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template <>
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struct GraphTraits<ArgumentGraph *> : public GraphTraits<ArgumentGraphNode *> {
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static NodeType *getEntryNode(ArgumentGraph *AG) {
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return AG->getEntryNode();
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}
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static ChildIteratorType nodes_begin(ArgumentGraph *AG) {
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return AG->begin();
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}
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static ChildIteratorType nodes_end(ArgumentGraph *AG) { return AG->end(); }
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};
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}
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/// Returns Attribute::None, Attribute::ReadOnly or Attribute::ReadNone.
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static Attribute::AttrKind
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determinePointerReadAttrs(Argument *A,
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const SmallPtrSet<Argument *, 8> &SCCNodes) {
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SmallVector<Use *, 32> Worklist;
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SmallSet<Use *, 32> Visited;
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// inalloca arguments are always clobbered by the call.
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if (A->hasInAllocaAttr())
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return Attribute::None;
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bool IsRead = false;
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// We don't need to track IsWritten. If A is written to, return immediately.
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for (Use &U : A->uses()) {
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Visited.insert(&U);
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Worklist.push_back(&U);
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}
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while (!Worklist.empty()) {
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Use *U = Worklist.pop_back_val();
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Instruction *I = cast<Instruction>(U->getUser());
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switch (I->getOpcode()) {
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case Instruction::BitCast:
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case Instruction::GetElementPtr:
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case Instruction::PHI:
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case Instruction::Select:
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case Instruction::AddrSpaceCast:
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// The original value is not read/written via this if the new value isn't.
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for (Use &UU : I->uses())
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if (Visited.insert(&UU).second)
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Worklist.push_back(&UU);
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break;
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case Instruction::Call:
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case Instruction::Invoke: {
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bool Captures = true;
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if (I->getType()->isVoidTy())
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Captures = false;
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auto AddUsersToWorklistIfCapturing = [&] {
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if (Captures)
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for (Use &UU : I->uses())
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if (Visited.insert(&UU).second)
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Worklist.push_back(&UU);
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};
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CallSite CS(I);
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if (CS.doesNotAccessMemory()) {
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AddUsersToWorklistIfCapturing();
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continue;
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}
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Function *F = CS.getCalledFunction();
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if (!F) {
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if (CS.onlyReadsMemory()) {
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IsRead = true;
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AddUsersToWorklistIfCapturing();
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continue;
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}
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return Attribute::None;
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}
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// Note: the callee and the two successor blocks *follow* the argument
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// operands. This means there is no need to adjust UseIndex to account
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// for these.
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unsigned UseIndex = std::distance(CS.arg_begin(), U);
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|
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// U cannot be the callee operand use: since we're exploring the
|
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// transitive uses of an Argument, having such a use be a callee would
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// imply the CallSite is an indirect call or invoke; and we'd take the
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// early exit above.
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assert(UseIndex < CS.data_operands_size() &&
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"Data operand use expected!");
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bool IsOperandBundleUse = UseIndex >= CS.getNumArgOperands();
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if (UseIndex >= F->arg_size() && !IsOperandBundleUse) {
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assert(F->isVarArg() && "More params than args in non-varargs call");
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return Attribute::None;
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}
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Captures &= !CS.doesNotCapture(UseIndex);
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// Since the optimizer (by design) cannot see the data flow corresponding
|
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// to a operand bundle use, these cannot participate in the optimistic SCC
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// analysis. Instead, we model the operand bundle uses as arguments in
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// call to a function external to the SCC.
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if (!SCCNodes.count(&*std::next(F->arg_begin(), UseIndex)) ||
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IsOperandBundleUse) {
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// The accessors used on CallSite here do the right thing for calls and
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// invokes with operand bundles.
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if (!CS.onlyReadsMemory() && !CS.onlyReadsMemory(UseIndex))
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return Attribute::None;
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if (!CS.doesNotAccessMemory(UseIndex))
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IsRead = true;
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}
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AddUsersToWorklistIfCapturing();
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break;
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}
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|
|
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case Instruction::Load:
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// A volatile load has side effects beyond what readonly can be relied
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// upon.
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if (cast<LoadInst>(I)->isVolatile())
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return Attribute::None;
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IsRead = true;
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break;
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case Instruction::ICmp:
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case Instruction::Ret:
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break;
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default:
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return Attribute::None;
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}
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}
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return IsRead ? Attribute::ReadOnly : Attribute::ReadNone;
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}
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|
|
/// Deduce nocapture attributes for the SCC.
|
|
static bool addArgumentAttrs(const SCCNodeSet &SCCNodes) {
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bool Changed = false;
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ArgumentGraph AG;
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AttrBuilder B;
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B.addAttribute(Attribute::NoCapture);
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|
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// Check each function in turn, determining which pointer arguments are not
|
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// captured.
|
|
for (Function *F : SCCNodes) {
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|
// We can infer and propagate function attributes only when we know that the
|
|
// definition we'll get at link time is *exactly* the definition we see now.
|
|
// For more details, see GlobalValue::mayBeDerefined.
|
|
if (!F->hasExactDefinition())
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continue;
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|
|
// Functions that are readonly (or readnone) and nounwind and don't return
|
|
// a value can't capture arguments. Don't analyze them.
|
|
if (F->onlyReadsMemory() && F->doesNotThrow() &&
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F->getReturnType()->isVoidTy()) {
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|
for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A != E;
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|
++A) {
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|
if (A->getType()->isPointerTy() && !A->hasNoCaptureAttr()) {
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A->addAttr(AttributeSet::get(F->getContext(), A->getArgNo() + 1, B));
|
|
++NumNoCapture;
|
|
Changed = true;
|
|
}
|
|
}
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continue;
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|
}
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|
|
for (Function::arg_iterator A = F->arg_begin(), E = F->arg_end(); A != E;
|
|
++A) {
|
|
if (!A->getType()->isPointerTy())
|
|
continue;
|
|
bool HasNonLocalUses = false;
|
|
if (!A->hasNoCaptureAttr()) {
|
|
ArgumentUsesTracker Tracker(SCCNodes);
|
|
PointerMayBeCaptured(&*A, &Tracker);
|
|
if (!Tracker.Captured) {
|
|
if (Tracker.Uses.empty()) {
|
|
// If it's trivially not captured, mark it nocapture now.
|
|
A->addAttr(
|
|
AttributeSet::get(F->getContext(), A->getArgNo() + 1, B));
|
|
++NumNoCapture;
|
|
Changed = true;
|
|
} else {
|
|
// If it's not trivially captured and not trivially not captured,
|
|
// then it must be calling into another function in our SCC. Save
|
|
// its particulars for Argument-SCC analysis later.
|
|
ArgumentGraphNode *Node = AG[&*A];
|
|
for (Argument *Use : Tracker.Uses) {
|
|
Node->Uses.push_back(AG[Use]);
|
|
if (Use != &*A)
|
|
HasNonLocalUses = true;
|
|
}
|
|
}
|
|
}
|
|
// Otherwise, it's captured. Don't bother doing SCC analysis on it.
|
|
}
|
|
if (!HasNonLocalUses && !A->onlyReadsMemory()) {
|
|
// Can we determine that it's readonly/readnone without doing an SCC?
|
|
// Note that we don't allow any calls at all here, or else our result
|
|
// will be dependent on the iteration order through the functions in the
|
|
// SCC.
|
|
SmallPtrSet<Argument *, 8> Self;
|
|
Self.insert(&*A);
|
|
Attribute::AttrKind R = determinePointerReadAttrs(&*A, Self);
|
|
if (R != Attribute::None) {
|
|
AttrBuilder B;
|
|
B.addAttribute(R);
|
|
A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
|
|
Changed = true;
|
|
R == Attribute::ReadOnly ? ++NumReadOnlyArg : ++NumReadNoneArg;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// The graph we've collected is partial because we stopped scanning for
|
|
// argument uses once we solved the argument trivially. These partial nodes
|
|
// show up as ArgumentGraphNode objects with an empty Uses list, and for
|
|
// these nodes the final decision about whether they capture has already been
|
|
// made. If the definition doesn't have a 'nocapture' attribute by now, it
|
|
// captures.
|
|
|
|
for (scc_iterator<ArgumentGraph *> I = scc_begin(&AG); !I.isAtEnd(); ++I) {
|
|
const std::vector<ArgumentGraphNode *> &ArgumentSCC = *I;
|
|
if (ArgumentSCC.size() == 1) {
|
|
if (!ArgumentSCC[0]->Definition)
|
|
continue; // synthetic root node
|
|
|
|
// eg. "void f(int* x) { if (...) f(x); }"
|
|
if (ArgumentSCC[0]->Uses.size() == 1 &&
|
|
ArgumentSCC[0]->Uses[0] == ArgumentSCC[0]) {
|
|
Argument *A = ArgumentSCC[0]->Definition;
|
|
A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
|
|
++NumNoCapture;
|
|
Changed = true;
|
|
}
|
|
continue;
|
|
}
|
|
|
|
bool SCCCaptured = false;
|
|
for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end();
|
|
I != E && !SCCCaptured; ++I) {
|
|
ArgumentGraphNode *Node = *I;
|
|
if (Node->Uses.empty()) {
|
|
if (!Node->Definition->hasNoCaptureAttr())
|
|
SCCCaptured = true;
|
|
}
|
|
}
|
|
if (SCCCaptured)
|
|
continue;
|
|
|
|
SmallPtrSet<Argument *, 8> ArgumentSCCNodes;
|
|
// Fill ArgumentSCCNodes with the elements of the ArgumentSCC. Used for
|
|
// quickly looking up whether a given Argument is in this ArgumentSCC.
|
|
for (ArgumentGraphNode *I : ArgumentSCC) {
|
|
ArgumentSCCNodes.insert(I->Definition);
|
|
}
|
|
|
|
for (auto I = ArgumentSCC.begin(), E = ArgumentSCC.end();
|
|
I != E && !SCCCaptured; ++I) {
|
|
ArgumentGraphNode *N = *I;
|
|
for (ArgumentGraphNode *Use : N->Uses) {
|
|
Argument *A = Use->Definition;
|
|
if (A->hasNoCaptureAttr() || ArgumentSCCNodes.count(A))
|
|
continue;
|
|
SCCCaptured = true;
|
|
break;
|
|
}
|
|
}
|
|
if (SCCCaptured)
|
|
continue;
|
|
|
|
for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
|
|
Argument *A = ArgumentSCC[i]->Definition;
|
|
A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
|
|
++NumNoCapture;
|
|
Changed = true;
|
|
}
|
|
|
|
// We also want to compute readonly/readnone. With a small number of false
|
|
// negatives, we can assume that any pointer which is captured isn't going
|
|
// to be provably readonly or readnone, since by definition we can't
|
|
// analyze all uses of a captured pointer.
|
|
//
|
|
// The false negatives happen when the pointer is captured by a function
|
|
// that promises readonly/readnone behaviour on the pointer, then the
|
|
// pointer's lifetime ends before anything that writes to arbitrary memory.
|
|
// Also, a readonly/readnone pointer may be returned, but returning a
|
|
// pointer is capturing it.
|
|
|
|
Attribute::AttrKind ReadAttr = Attribute::ReadNone;
|
|
for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
|
|
Argument *A = ArgumentSCC[i]->Definition;
|
|
Attribute::AttrKind K = determinePointerReadAttrs(A, ArgumentSCCNodes);
|
|
if (K == Attribute::ReadNone)
|
|
continue;
|
|
if (K == Attribute::ReadOnly) {
|
|
ReadAttr = Attribute::ReadOnly;
|
|
continue;
|
|
}
|
|
ReadAttr = K;
|
|
break;
|
|
}
|
|
|
|
if (ReadAttr != Attribute::None) {
|
|
AttrBuilder B, R;
|
|
B.addAttribute(ReadAttr);
|
|
R.addAttribute(Attribute::ReadOnly).addAttribute(Attribute::ReadNone);
|
|
for (unsigned i = 0, e = ArgumentSCC.size(); i != e; ++i) {
|
|
Argument *A = ArgumentSCC[i]->Definition;
|
|
// Clear out existing readonly/readnone attributes
|
|
A->removeAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, R));
|
|
A->addAttr(AttributeSet::get(A->getContext(), A->getArgNo() + 1, B));
|
|
ReadAttr == Attribute::ReadOnly ? ++NumReadOnlyArg : ++NumReadNoneArg;
|
|
Changed = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
/// Tests whether a function is "malloc-like".
|
|
///
|
|
/// A function is "malloc-like" if it returns either null or a pointer that
|
|
/// doesn't alias any other pointer visible to the caller.
|
|
static bool isFunctionMallocLike(Function *F, const SCCNodeSet &SCCNodes) {
|
|
SmallSetVector<Value *, 8> FlowsToReturn;
|
|
for (BasicBlock &BB : *F)
|
|
if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))
|
|
FlowsToReturn.insert(Ret->getReturnValue());
|
|
|
|
for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
|
|
Value *RetVal = FlowsToReturn[i];
|
|
|
|
if (Constant *C = dyn_cast<Constant>(RetVal)) {
|
|
if (!C->isNullValue() && !isa<UndefValue>(C))
|
|
return false;
|
|
|
|
continue;
|
|
}
|
|
|
|
if (isa<Argument>(RetVal))
|
|
return false;
|
|
|
|
if (Instruction *RVI = dyn_cast<Instruction>(RetVal))
|
|
switch (RVI->getOpcode()) {
|
|
// Extend the analysis by looking upwards.
|
|
case Instruction::BitCast:
|
|
case Instruction::GetElementPtr:
|
|
case Instruction::AddrSpaceCast:
|
|
FlowsToReturn.insert(RVI->getOperand(0));
|
|
continue;
|
|
case Instruction::Select: {
|
|
SelectInst *SI = cast<SelectInst>(RVI);
|
|
FlowsToReturn.insert(SI->getTrueValue());
|
|
FlowsToReturn.insert(SI->getFalseValue());
|
|
continue;
|
|
}
|
|
case Instruction::PHI: {
|
|
PHINode *PN = cast<PHINode>(RVI);
|
|
for (Value *IncValue : PN->incoming_values())
|
|
FlowsToReturn.insert(IncValue);
|
|
continue;
|
|
}
|
|
|
|
// Check whether the pointer came from an allocation.
|
|
case Instruction::Alloca:
|
|
break;
|
|
case Instruction::Call:
|
|
case Instruction::Invoke: {
|
|
CallSite CS(RVI);
|
|
if (CS.paramHasAttr(0, Attribute::NoAlias))
|
|
break;
|
|
if (CS.getCalledFunction() && SCCNodes.count(CS.getCalledFunction()))
|
|
break;
|
|
} // fall-through
|
|
default:
|
|
return false; // Did not come from an allocation.
|
|
}
|
|
|
|
if (PointerMayBeCaptured(RetVal, false, /*StoreCaptures=*/false))
|
|
return false;
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Deduce noalias attributes for the SCC.
|
|
static bool addNoAliasAttrs(const SCCNodeSet &SCCNodes) {
|
|
// Check each function in turn, determining which functions return noalias
|
|
// pointers.
|
|
for (Function *F : SCCNodes) {
|
|
// Already noalias.
|
|
if (F->doesNotAlias(0))
|
|
continue;
|
|
|
|
// We can infer and propagate function attributes only when we know that the
|
|
// definition we'll get at link time is *exactly* the definition we see now.
|
|
// For more details, see GlobalValue::mayBeDerefined.
|
|
if (!F->hasExactDefinition())
|
|
return false;
|
|
|
|
// We annotate noalias return values, which are only applicable to
|
|
// pointer types.
|
|
if (!F->getReturnType()->isPointerTy())
|
|
continue;
|
|
|
|
if (!isFunctionMallocLike(F, SCCNodes))
|
|
return false;
|
|
}
|
|
|
|
bool MadeChange = false;
|
|
for (Function *F : SCCNodes) {
|
|
if (F->doesNotAlias(0) || !F->getReturnType()->isPointerTy())
|
|
continue;
|
|
|
|
F->setDoesNotAlias(0);
|
|
++NumNoAlias;
|
|
MadeChange = true;
|
|
}
|
|
|
|
return MadeChange;
|
|
}
|
|
|
|
/// Tests whether this function is known to not return null.
|
|
///
|
|
/// Requires that the function returns a pointer.
|
|
///
|
|
/// Returns true if it believes the function will not return a null, and sets
|
|
/// \p Speculative based on whether the returned conclusion is a speculative
|
|
/// conclusion due to SCC calls.
|
|
static bool isReturnNonNull(Function *F, const SCCNodeSet &SCCNodes,
|
|
bool &Speculative) {
|
|
assert(F->getReturnType()->isPointerTy() &&
|
|
"nonnull only meaningful on pointer types");
|
|
Speculative = false;
|
|
|
|
SmallSetVector<Value *, 8> FlowsToReturn;
|
|
for (BasicBlock &BB : *F)
|
|
if (auto *Ret = dyn_cast<ReturnInst>(BB.getTerminator()))
|
|
FlowsToReturn.insert(Ret->getReturnValue());
|
|
|
|
for (unsigned i = 0; i != FlowsToReturn.size(); ++i) {
|
|
Value *RetVal = FlowsToReturn[i];
|
|
|
|
// If this value is locally known to be non-null, we're good
|
|
if (isKnownNonNull(RetVal))
|
|
continue;
|
|
|
|
// Otherwise, we need to look upwards since we can't make any local
|
|
// conclusions.
|
|
Instruction *RVI = dyn_cast<Instruction>(RetVal);
|
|
if (!RVI)
|
|
return false;
|
|
switch (RVI->getOpcode()) {
|
|
// Extend the analysis by looking upwards.
|
|
case Instruction::BitCast:
|
|
case Instruction::GetElementPtr:
|
|
case Instruction::AddrSpaceCast:
|
|
FlowsToReturn.insert(RVI->getOperand(0));
|
|
continue;
|
|
case Instruction::Select: {
|
|
SelectInst *SI = cast<SelectInst>(RVI);
|
|
FlowsToReturn.insert(SI->getTrueValue());
|
|
FlowsToReturn.insert(SI->getFalseValue());
|
|
continue;
|
|
}
|
|
case Instruction::PHI: {
|
|
PHINode *PN = cast<PHINode>(RVI);
|
|
for (int i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
FlowsToReturn.insert(PN->getIncomingValue(i));
|
|
continue;
|
|
}
|
|
case Instruction::Call:
|
|
case Instruction::Invoke: {
|
|
CallSite CS(RVI);
|
|
Function *Callee = CS.getCalledFunction();
|
|
// A call to a node within the SCC is assumed to return null until
|
|
// proven otherwise
|
|
if (Callee && SCCNodes.count(Callee)) {
|
|
Speculative = true;
|
|
continue;
|
|
}
|
|
return false;
|
|
}
|
|
default:
|
|
return false; // Unknown source, may be null
|
|
};
|
|
llvm_unreachable("should have either continued or returned");
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Deduce nonnull attributes for the SCC.
|
|
static bool addNonNullAttrs(const SCCNodeSet &SCCNodes) {
|
|
// Speculative that all functions in the SCC return only nonnull
|
|
// pointers. We may refute this as we analyze functions.
|
|
bool SCCReturnsNonNull = true;
|
|
|
|
bool MadeChange = false;
|
|
|
|
// Check each function in turn, determining which functions return nonnull
|
|
// pointers.
|
|
for (Function *F : SCCNodes) {
|
|
// Already nonnull.
|
|
if (F->getAttributes().hasAttribute(AttributeSet::ReturnIndex,
|
|
Attribute::NonNull))
|
|
continue;
|
|
|
|
// We can infer and propagate function attributes only when we know that the
|
|
// definition we'll get at link time is *exactly* the definition we see now.
|
|
// For more details, see GlobalValue::mayBeDerefined.
|
|
if (!F->hasExactDefinition())
|
|
return false;
|
|
|
|
// We annotate nonnull return values, which are only applicable to
|
|
// pointer types.
|
|
if (!F->getReturnType()->isPointerTy())
|
|
continue;
|
|
|
|
bool Speculative = false;
|
|
if (isReturnNonNull(F, SCCNodes, Speculative)) {
|
|
if (!Speculative) {
|
|
// Mark the function eagerly since we may discover a function
|
|
// which prevents us from speculating about the entire SCC
|
|
DEBUG(dbgs() << "Eagerly marking " << F->getName() << " as nonnull\n");
|
|
F->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);
|
|
++NumNonNullReturn;
|
|
MadeChange = true;
|
|
}
|
|
continue;
|
|
}
|
|
// At least one function returns something which could be null, can't
|
|
// speculate any more.
|
|
SCCReturnsNonNull = false;
|
|
}
|
|
|
|
if (SCCReturnsNonNull) {
|
|
for (Function *F : SCCNodes) {
|
|
if (F->getAttributes().hasAttribute(AttributeSet::ReturnIndex,
|
|
Attribute::NonNull) ||
|
|
!F->getReturnType()->isPointerTy())
|
|
continue;
|
|
|
|
DEBUG(dbgs() << "SCC marking " << F->getName() << " as nonnull\n");
|
|
F->addAttribute(AttributeSet::ReturnIndex, Attribute::NonNull);
|
|
++NumNonNullReturn;
|
|
MadeChange = true;
|
|
}
|
|
}
|
|
|
|
return MadeChange;
|
|
}
|
|
|
|
/// Remove the convergent attribute from all functions in the SCC if every
|
|
/// callsite within the SCC is not convergent (except for calls to functions
|
|
/// within the SCC). Returns true if changes were made.
|
|
static bool removeConvergentAttrs(const SCCNodeSet &SCCNodes) {
|
|
// For every function in SCC, ensure that either
|
|
// * it is not convergent, or
|
|
// * we can remove its convergent attribute.
|
|
bool HasConvergentFn = false;
|
|
for (Function *F : SCCNodes) {
|
|
if (!F->isConvergent()) continue;
|
|
HasConvergentFn = true;
|
|
|
|
// Can't remove convergent from function declarations.
|
|
if (F->isDeclaration()) return false;
|
|
|
|
// Can't remove convergent if any of our functions has a convergent call to a
|
|
// function not in the SCC.
|
|
for (Instruction &I : instructions(*F)) {
|
|
CallSite CS(&I);
|
|
// Bail if CS is a convergent call to a function not in the SCC.
|
|
if (CS && CS.isConvergent() &&
|
|
SCCNodes.count(CS.getCalledFunction()) == 0)
|
|
return false;
|
|
}
|
|
}
|
|
|
|
// If the SCC doesn't have any convergent functions, we have nothing to do.
|
|
if (!HasConvergentFn) return false;
|
|
|
|
// If we got here, all of the calls the SCC makes to functions not in the SCC
|
|
// are non-convergent. Therefore all of the SCC's functions can also be made
|
|
// non-convergent. We'll remove the attr from the callsites in
|
|
// InstCombineCalls.
|
|
for (Function *F : SCCNodes) {
|
|
if (!F->isConvergent()) continue;
|
|
|
|
DEBUG(dbgs() << "Removing convergent attr from fn " << F->getName()
|
|
<< "\n");
|
|
F->setNotConvergent();
|
|
}
|
|
return true;
|
|
}
|
|
|
|
static bool setDoesNotRecurse(Function &F) {
|
|
if (F.doesNotRecurse())
|
|
return false;
|
|
F.setDoesNotRecurse();
|
|
++NumNoRecurse;
|
|
return true;
|
|
}
|
|
|
|
static bool addNoRecurseAttrs(const SCCNodeSet &SCCNodes) {
|
|
// Try and identify functions that do not recurse.
|
|
|
|
// If the SCC contains multiple nodes we know for sure there is recursion.
|
|
if (SCCNodes.size() != 1)
|
|
return false;
|
|
|
|
Function *F = *SCCNodes.begin();
|
|
if (!F || F->isDeclaration() || F->doesNotRecurse())
|
|
return false;
|
|
|
|
// If all of the calls in F are identifiable and are to norecurse functions, F
|
|
// is norecurse. This check also detects self-recursion as F is not currently
|
|
// marked norecurse, so any called from F to F will not be marked norecurse.
|
|
for (Instruction &I : instructions(*F))
|
|
if (auto CS = CallSite(&I)) {
|
|
Function *Callee = CS.getCalledFunction();
|
|
if (!Callee || Callee == F || !Callee->doesNotRecurse())
|
|
// Function calls a potentially recursive function.
|
|
return false;
|
|
}
|
|
|
|
// Every call was to a non-recursive function other than this function, and
|
|
// we have no indirect recursion as the SCC size is one. This function cannot
|
|
// recurse.
|
|
return setDoesNotRecurse(*F);
|
|
}
|
|
|
|
PreservedAnalyses PostOrderFunctionAttrsPass::run(LazyCallGraph::SCC &C,
|
|
CGSCCAnalysisManager &AM) {
|
|
FunctionAnalysisManager &FAM =
|
|
AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C).getManager();
|
|
|
|
// We pass a lambda into functions to wire them up to the analysis manager
|
|
// for getting function analyses.
|
|
auto AARGetter = [&](Function &F) -> AAResults & {
|
|
return FAM.getResult<AAManager>(F);
|
|
};
|
|
|
|
// Fill SCCNodes with the elements of the SCC. Also track whether there are
|
|
// any external or opt-none nodes that will prevent us from optimizing any
|
|
// part of the SCC.
|
|
SCCNodeSet SCCNodes;
|
|
bool HasUnknownCall = false;
|
|
for (LazyCallGraph::Node &N : C) {
|
|
Function &F = N.getFunction();
|
|
if (F.hasFnAttribute(Attribute::OptimizeNone)) {
|
|
// Treat any function we're trying not to optimize as if it were an
|
|
// indirect call and omit it from the node set used below.
|
|
HasUnknownCall = true;
|
|
continue;
|
|
}
|
|
// Track whether any functions in this SCC have an unknown call edge.
|
|
// Note: if this is ever a performance hit, we can common it with
|
|
// subsequent routines which also do scans over the instructions of the
|
|
// function.
|
|
if (!HasUnknownCall)
|
|
for (Instruction &I : instructions(F))
|
|
if (auto CS = CallSite(&I))
|
|
if (!CS.getCalledFunction()) {
|
|
HasUnknownCall = true;
|
|
break;
|
|
}
|
|
|
|
SCCNodes.insert(&F);
|
|
}
|
|
|
|
bool Changed = false;
|
|
Changed |= addReadAttrs(SCCNodes, AARGetter);
|
|
Changed |= addArgumentAttrs(SCCNodes);
|
|
|
|
// If we have no external nodes participating in the SCC, we can deduce some
|
|
// more precise attributes as well.
|
|
if (!HasUnknownCall) {
|
|
Changed |= addNoAliasAttrs(SCCNodes);
|
|
Changed |= addNonNullAttrs(SCCNodes);
|
|
Changed |= removeConvergentAttrs(SCCNodes);
|
|
Changed |= addNoRecurseAttrs(SCCNodes);
|
|
}
|
|
|
|
return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
|
|
}
|
|
|
|
namespace {
|
|
struct PostOrderFunctionAttrsLegacyPass : public CallGraphSCCPass {
|
|
static char ID; // Pass identification, replacement for typeid
|
|
PostOrderFunctionAttrsLegacyPass() : CallGraphSCCPass(ID) {
|
|
initializePostOrderFunctionAttrsLegacyPassPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
bool runOnSCC(CallGraphSCC &SCC) override;
|
|
|
|
void getAnalysisUsage(AnalysisUsage &AU) const override {
|
|
AU.setPreservesCFG();
|
|
AU.addRequired<AssumptionCacheTracker>();
|
|
getAAResultsAnalysisUsage(AU);
|
|
CallGraphSCCPass::getAnalysisUsage(AU);
|
|
}
|
|
};
|
|
}
|
|
|
|
char PostOrderFunctionAttrsLegacyPass::ID = 0;
|
|
INITIALIZE_PASS_BEGIN(PostOrderFunctionAttrsLegacyPass, "functionattrs",
|
|
"Deduce function attributes", false, false)
|
|
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
|
|
INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
|
|
INITIALIZE_PASS_END(PostOrderFunctionAttrsLegacyPass, "functionattrs",
|
|
"Deduce function attributes", false, false)
|
|
|
|
Pass *llvm::createPostOrderFunctionAttrsLegacyPass() { return new PostOrderFunctionAttrsLegacyPass(); }
|
|
|
|
template <typename AARGetterT>
|
|
static bool runImpl(CallGraphSCC &SCC, AARGetterT AARGetter) {
|
|
bool Changed = false;
|
|
|
|
// Fill SCCNodes with the elements of the SCC. Used for quickly looking up
|
|
// whether a given CallGraphNode is in this SCC. Also track whether there are
|
|
// any external or opt-none nodes that will prevent us from optimizing any
|
|
// part of the SCC.
|
|
SCCNodeSet SCCNodes;
|
|
bool ExternalNode = false;
|
|
for (CallGraphNode *I : SCC) {
|
|
Function *F = I->getFunction();
|
|
if (!F || F->hasFnAttribute(Attribute::OptimizeNone)) {
|
|
// External node or function we're trying not to optimize - we both avoid
|
|
// transform them and avoid leveraging information they provide.
|
|
ExternalNode = true;
|
|
continue;
|
|
}
|
|
|
|
SCCNodes.insert(F);
|
|
}
|
|
|
|
Changed |= addReadAttrs(SCCNodes, AARGetter);
|
|
Changed |= addArgumentAttrs(SCCNodes);
|
|
|
|
// If we have no external nodes participating in the SCC, we can deduce some
|
|
// more precise attributes as well.
|
|
if (!ExternalNode) {
|
|
Changed |= addNoAliasAttrs(SCCNodes);
|
|
Changed |= addNonNullAttrs(SCCNodes);
|
|
Changed |= removeConvergentAttrs(SCCNodes);
|
|
Changed |= addNoRecurseAttrs(SCCNodes);
|
|
}
|
|
|
|
return Changed;
|
|
}
|
|
|
|
bool PostOrderFunctionAttrsLegacyPass::runOnSCC(CallGraphSCC &SCC) {
|
|
if (skipSCC(SCC))
|
|
return false;
|
|
|
|
// We compute dedicated AA results for each function in the SCC as needed. We
|
|
// use a lambda referencing external objects so that they live long enough to
|
|
// be queried, but we re-use them each time.
|
|
Optional<BasicAAResult> BAR;
|
|
Optional<AAResults> AAR;
|
|
auto AARGetter = [&](Function &F) -> AAResults & {
|
|
BAR.emplace(createLegacyPMBasicAAResult(*this, F));
|
|
AAR.emplace(createLegacyPMAAResults(*this, F, *BAR));
|
|
return *AAR;
|
|
};
|
|
|
|
return runImpl(SCC, AARGetter);
|
|
}
|
|
|
|
namespace {
|
|
struct ReversePostOrderFunctionAttrsLegacyPass : public ModulePass {
|
|
static char ID; // Pass identification, replacement for typeid
|
|
ReversePostOrderFunctionAttrsLegacyPass() : ModulePass(ID) {
|
|
initializeReversePostOrderFunctionAttrsLegacyPassPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
bool runOnModule(Module &M) override;
|
|
|
|
void getAnalysisUsage(AnalysisUsage &AU) const override {
|
|
AU.setPreservesCFG();
|
|
AU.addRequired<CallGraphWrapperPass>();
|
|
AU.addPreserved<CallGraphWrapperPass>();
|
|
}
|
|
};
|
|
}
|
|
|
|
char ReversePostOrderFunctionAttrsLegacyPass::ID = 0;
|
|
INITIALIZE_PASS_BEGIN(ReversePostOrderFunctionAttrsLegacyPass, "rpo-functionattrs",
|
|
"Deduce function attributes in RPO", false, false)
|
|
INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
|
|
INITIALIZE_PASS_END(ReversePostOrderFunctionAttrsLegacyPass, "rpo-functionattrs",
|
|
"Deduce function attributes in RPO", false, false)
|
|
|
|
Pass *llvm::createReversePostOrderFunctionAttrsPass() {
|
|
return new ReversePostOrderFunctionAttrsLegacyPass();
|
|
}
|
|
|
|
static bool addNoRecurseAttrsTopDown(Function &F) {
|
|
// We check the preconditions for the function prior to calling this to avoid
|
|
// the cost of building up a reversible post-order list. We assert them here
|
|
// to make sure none of the invariants this relies on were violated.
|
|
assert(!F.isDeclaration() && "Cannot deduce norecurse without a definition!");
|
|
assert(!F.doesNotRecurse() &&
|
|
"This function has already been deduced as norecurs!");
|
|
assert(F.hasInternalLinkage() &&
|
|
"Can only do top-down deduction for internal linkage functions!");
|
|
|
|
// If F is internal and all of its uses are calls from a non-recursive
|
|
// functions, then none of its calls could in fact recurse without going
|
|
// through a function marked norecurse, and so we can mark this function too
|
|
// as norecurse. Note that the uses must actually be calls -- otherwise
|
|
// a pointer to this function could be returned from a norecurse function but
|
|
// this function could be recursively (indirectly) called. Note that this
|
|
// also detects if F is directly recursive as F is not yet marked as
|
|
// a norecurse function.
|
|
for (auto *U : F.users()) {
|
|
auto *I = dyn_cast<Instruction>(U);
|
|
if (!I)
|
|
return false;
|
|
CallSite CS(I);
|
|
if (!CS || !CS.getParent()->getParent()->doesNotRecurse())
|
|
return false;
|
|
}
|
|
return setDoesNotRecurse(F);
|
|
}
|
|
|
|
static bool deduceFunctionAttributeInRPO(Module &M, CallGraph &CG) {
|
|
// We only have a post-order SCC traversal (because SCCs are inherently
|
|
// discovered in post-order), so we accumulate them in a vector and then walk
|
|
// it in reverse. This is simpler than using the RPO iterator infrastructure
|
|
// because we need to combine SCC detection and the PO walk of the call
|
|
// graph. We can also cheat egregiously because we're primarily interested in
|
|
// synthesizing norecurse and so we can only save the singular SCCs as SCCs
|
|
// with multiple functions in them will clearly be recursive.
|
|
SmallVector<Function *, 16> Worklist;
|
|
for (scc_iterator<CallGraph *> I = scc_begin(&CG); !I.isAtEnd(); ++I) {
|
|
if (I->size() != 1)
|
|
continue;
|
|
|
|
Function *F = I->front()->getFunction();
|
|
if (F && !F->isDeclaration() && !F->doesNotRecurse() &&
|
|
F->hasInternalLinkage())
|
|
Worklist.push_back(F);
|
|
}
|
|
|
|
bool Changed = false;
|
|
for (auto *F : reverse(Worklist))
|
|
Changed |= addNoRecurseAttrsTopDown(*F);
|
|
|
|
return Changed;
|
|
}
|
|
|
|
bool ReversePostOrderFunctionAttrsLegacyPass::runOnModule(Module &M) {
|
|
if (skipModule(M))
|
|
return false;
|
|
|
|
auto &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
|
|
|
|
return deduceFunctionAttributeInRPO(M, CG);
|
|
}
|
|
|
|
PreservedAnalyses
|
|
ReversePostOrderFunctionAttrsPass::run(Module &M, AnalysisManager<Module> &AM) {
|
|
auto &CG = AM.getResult<CallGraphAnalysis>(M);
|
|
|
|
bool Changed = deduceFunctionAttributeInRPO(M, CG);
|
|
if (!Changed)
|
|
return PreservedAnalyses::all();
|
|
PreservedAnalyses PA;
|
|
PA.preserve<CallGraphAnalysis>();
|
|
return PA;
|
|
}
|