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753 lines
30 KiB
753 lines
30 KiB
//===----------------- LoopRotationUtils.cpp -----------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file provides utilities to convert a loop into a loop with bottom test.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Utils/LoopRotationUtils.h"
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#include "llvm/ADT/Statistic.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/CodeMetrics.h"
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#include "llvm/Analysis/DomTreeUpdater.h"
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#include "llvm/Analysis/GlobalsModRef.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/MemorySSA.h"
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#include "llvm/Analysis/MemorySSAUpdater.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/CFG.h"
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#include "llvm/IR/DebugInfoMetadata.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Support/CommandLine.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/Transforms/Utils/BasicBlockUtils.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Transforms/Utils/LoopUtils.h"
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#include "llvm/Transforms/Utils/SSAUpdater.h"
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#include "llvm/Transforms/Utils/ValueMapper.h"
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using namespace llvm;
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#define DEBUG_TYPE "loop-rotate"
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STATISTIC(NumNotRotatedDueToHeaderSize,
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"Number of loops not rotated due to the header size");
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STATISTIC(NumRotated, "Number of loops rotated");
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static cl::opt<bool>
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MultiRotate("loop-rotate-multi", cl::init(false), cl::Hidden,
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cl::desc("Allow loop rotation multiple times in order to reach "
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"a better latch exit"));
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namespace {
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/// A simple loop rotation transformation.
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class LoopRotate {
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const unsigned MaxHeaderSize;
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LoopInfo *LI;
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const TargetTransformInfo *TTI;
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AssumptionCache *AC;
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DominatorTree *DT;
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ScalarEvolution *SE;
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MemorySSAUpdater *MSSAU;
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const SimplifyQuery &SQ;
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bool RotationOnly;
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bool IsUtilMode;
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public:
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LoopRotate(unsigned MaxHeaderSize, LoopInfo *LI,
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const TargetTransformInfo *TTI, AssumptionCache *AC,
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DominatorTree *DT, ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
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const SimplifyQuery &SQ, bool RotationOnly, bool IsUtilMode)
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: MaxHeaderSize(MaxHeaderSize), LI(LI), TTI(TTI), AC(AC), DT(DT), SE(SE),
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MSSAU(MSSAU), SQ(SQ), RotationOnly(RotationOnly),
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IsUtilMode(IsUtilMode) {}
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bool processLoop(Loop *L);
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private:
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bool rotateLoop(Loop *L, bool SimplifiedLatch);
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bool simplifyLoopLatch(Loop *L);
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};
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} // end anonymous namespace
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/// Insert (K, V) pair into the ValueToValueMap, and verify the key did not
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/// previously exist in the map, and the value was inserted.
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static void InsertNewValueIntoMap(ValueToValueMapTy &VM, Value *K, Value *V) {
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bool Inserted = VM.insert({K, V}).second;
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assert(Inserted);
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(void)Inserted;
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}
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/// RewriteUsesOfClonedInstructions - We just cloned the instructions from the
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/// old header into the preheader. If there were uses of the values produced by
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/// these instruction that were outside of the loop, we have to insert PHI nodes
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/// to merge the two values. Do this now.
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static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
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BasicBlock *OrigPreheader,
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ValueToValueMapTy &ValueMap,
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SmallVectorImpl<PHINode*> *InsertedPHIs) {
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// Remove PHI node entries that are no longer live.
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BasicBlock::iterator I, E = OrigHeader->end();
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for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
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PN->removeIncomingValue(PN->getBasicBlockIndex(OrigPreheader));
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// Now fix up users of the instructions in OrigHeader, inserting PHI nodes
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// as necessary.
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SSAUpdater SSA(InsertedPHIs);
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for (I = OrigHeader->begin(); I != E; ++I) {
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Value *OrigHeaderVal = &*I;
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// If there are no uses of the value (e.g. because it returns void), there
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// is nothing to rewrite.
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if (OrigHeaderVal->use_empty())
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continue;
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Value *OrigPreHeaderVal = ValueMap.lookup(OrigHeaderVal);
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// The value now exits in two versions: the initial value in the preheader
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// and the loop "next" value in the original header.
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SSA.Initialize(OrigHeaderVal->getType(), OrigHeaderVal->getName());
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SSA.AddAvailableValue(OrigHeader, OrigHeaderVal);
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SSA.AddAvailableValue(OrigPreheader, OrigPreHeaderVal);
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// Visit each use of the OrigHeader instruction.
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for (Value::use_iterator UI = OrigHeaderVal->use_begin(),
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UE = OrigHeaderVal->use_end();
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UI != UE;) {
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// Grab the use before incrementing the iterator.
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Use &U = *UI;
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// Increment the iterator before removing the use from the list.
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++UI;
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// SSAUpdater can't handle a non-PHI use in the same block as an
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// earlier def. We can easily handle those cases manually.
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Instruction *UserInst = cast<Instruction>(U.getUser());
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if (!isa<PHINode>(UserInst)) {
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BasicBlock *UserBB = UserInst->getParent();
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// The original users in the OrigHeader are already using the
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// original definitions.
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if (UserBB == OrigHeader)
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continue;
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// Users in the OrigPreHeader need to use the value to which the
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// original definitions are mapped.
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if (UserBB == OrigPreheader) {
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U = OrigPreHeaderVal;
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continue;
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}
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}
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// Anything else can be handled by SSAUpdater.
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SSA.RewriteUse(U);
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}
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// Replace MetadataAsValue(ValueAsMetadata(OrigHeaderVal)) uses in debug
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// intrinsics.
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SmallVector<DbgValueInst *, 1> DbgValues;
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llvm::findDbgValues(DbgValues, OrigHeaderVal);
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for (auto &DbgValue : DbgValues) {
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// The original users in the OrigHeader are already using the original
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// definitions.
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BasicBlock *UserBB = DbgValue->getParent();
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if (UserBB == OrigHeader)
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continue;
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// Users in the OrigPreHeader need to use the value to which the
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// original definitions are mapped and anything else can be handled by
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// the SSAUpdater. To avoid adding PHINodes, check if the value is
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// available in UserBB, if not substitute undef.
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Value *NewVal;
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if (UserBB == OrigPreheader)
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NewVal = OrigPreHeaderVal;
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else if (SSA.HasValueForBlock(UserBB))
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NewVal = SSA.GetValueInMiddleOfBlock(UserBB);
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else
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NewVal = UndefValue::get(OrigHeaderVal->getType());
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DbgValue->setOperand(0,
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MetadataAsValue::get(OrigHeaderVal->getContext(),
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ValueAsMetadata::get(NewVal)));
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}
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}
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}
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// Assuming both header and latch are exiting, look for a phi which is only
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// used outside the loop (via a LCSSA phi) in the exit from the header.
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// This means that rotating the loop can remove the phi.
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static bool profitableToRotateLoopExitingLatch(Loop *L) {
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BasicBlock *Header = L->getHeader();
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BranchInst *BI = dyn_cast<BranchInst>(Header->getTerminator());
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assert(BI && BI->isConditional() && "need header with conditional exit");
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BasicBlock *HeaderExit = BI->getSuccessor(0);
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if (L->contains(HeaderExit))
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HeaderExit = BI->getSuccessor(1);
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for (auto &Phi : Header->phis()) {
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// Look for uses of this phi in the loop/via exits other than the header.
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if (llvm::any_of(Phi.users(), [HeaderExit](const User *U) {
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return cast<Instruction>(U)->getParent() != HeaderExit;
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}))
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continue;
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return true;
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}
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return false;
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}
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// Check that latch exit is deoptimizing (which means - very unlikely to happen)
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// and there is another exit from the loop which is non-deoptimizing.
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// If we rotate latch to that exit our loop has a better chance of being fully
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// canonical.
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//
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// It can give false positives in some rare cases.
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static bool canRotateDeoptimizingLatchExit(Loop *L) {
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BasicBlock *Latch = L->getLoopLatch();
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assert(Latch && "need latch");
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BranchInst *BI = dyn_cast<BranchInst>(Latch->getTerminator());
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// Need normal exiting latch.
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if (!BI || !BI->isConditional())
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return false;
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BasicBlock *Exit = BI->getSuccessor(1);
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if (L->contains(Exit))
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Exit = BI->getSuccessor(0);
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// Latch exit is non-deoptimizing, no need to rotate.
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if (!Exit->getPostdominatingDeoptimizeCall())
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return false;
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SmallVector<BasicBlock *, 4> Exits;
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L->getUniqueExitBlocks(Exits);
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if (!Exits.empty()) {
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// There is at least one non-deoptimizing exit.
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//
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// Note, that BasicBlock::getPostdominatingDeoptimizeCall is not exact,
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// as it can conservatively return false for deoptimizing exits with
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// complex enough control flow down to deoptimize call.
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//
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// That means here we can report success for a case where
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// all exits are deoptimizing but one of them has complex enough
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// control flow (e.g. with loops).
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//
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// That should be a very rare case and false positives for this function
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// have compile-time effect only.
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return any_of(Exits, [](const BasicBlock *BB) {
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return !BB->getPostdominatingDeoptimizeCall();
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});
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}
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return false;
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}
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/// Rotate loop LP. Return true if the loop is rotated.
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///
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/// \param SimplifiedLatch is true if the latch was just folded into the final
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/// loop exit. In this case we may want to rotate even though the new latch is
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/// now an exiting branch. This rotation would have happened had the latch not
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/// been simplified. However, if SimplifiedLatch is false, then we avoid
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/// rotating loops in which the latch exits to avoid excessive or endless
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/// rotation. LoopRotate should be repeatable and converge to a canonical
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/// form. This property is satisfied because simplifying the loop latch can only
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/// happen once across multiple invocations of the LoopRotate pass.
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///
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/// If -loop-rotate-multi is enabled we can do multiple rotations in one go
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/// so to reach a suitable (non-deoptimizing) exit.
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bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
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// If the loop has only one block then there is not much to rotate.
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if (L->getBlocks().size() == 1)
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return false;
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bool Rotated = false;
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do {
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BasicBlock *OrigHeader = L->getHeader();
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BasicBlock *OrigLatch = L->getLoopLatch();
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BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
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if (!BI || BI->isUnconditional())
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return Rotated;
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// If the loop header is not one of the loop exiting blocks then
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// either this loop is already rotated or it is not
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// suitable for loop rotation transformations.
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if (!L->isLoopExiting(OrigHeader))
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return Rotated;
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// If the loop latch already contains a branch that leaves the loop then the
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// loop is already rotated.
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if (!OrigLatch)
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return Rotated;
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// Rotate if either the loop latch does *not* exit the loop, or if the loop
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// latch was just simplified. Or if we think it will be profitable.
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if (L->isLoopExiting(OrigLatch) && !SimplifiedLatch && IsUtilMode == false &&
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!profitableToRotateLoopExitingLatch(L) &&
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!canRotateDeoptimizingLatchExit(L))
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return Rotated;
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// Check size of original header and reject loop if it is very big or we can't
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// duplicate blocks inside it.
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{
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SmallPtrSet<const Value *, 32> EphValues;
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CodeMetrics::collectEphemeralValues(L, AC, EphValues);
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CodeMetrics Metrics;
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Metrics.analyzeBasicBlock(OrigHeader, *TTI, EphValues);
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if (Metrics.notDuplicatable) {
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LLVM_DEBUG(
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dbgs() << "LoopRotation: NOT rotating - contains non-duplicatable"
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<< " instructions: ";
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L->dump());
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return Rotated;
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}
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if (Metrics.convergent) {
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LLVM_DEBUG(dbgs() << "LoopRotation: NOT rotating - contains convergent "
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"instructions: ";
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L->dump());
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return Rotated;
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}
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if (Metrics.NumInsts > MaxHeaderSize) {
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LLVM_DEBUG(dbgs() << "LoopRotation: NOT rotating - contains "
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<< Metrics.NumInsts
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<< " instructions, which is more than the threshold ("
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<< MaxHeaderSize << " instructions): ";
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L->dump());
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++NumNotRotatedDueToHeaderSize;
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return Rotated;
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}
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}
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// Now, this loop is suitable for rotation.
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BasicBlock *OrigPreheader = L->getLoopPreheader();
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// If the loop could not be converted to canonical form, it must have an
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// indirectbr in it, just give up.
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if (!OrigPreheader || !L->hasDedicatedExits())
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return Rotated;
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// Anything ScalarEvolution may know about this loop or the PHI nodes
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// in its header will soon be invalidated. We should also invalidate
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// all outer loops because insertion and deletion of blocks that happens
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// during the rotation may violate invariants related to backedge taken
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// infos in them.
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if (SE)
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SE->forgetTopmostLoop(L);
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LLVM_DEBUG(dbgs() << "LoopRotation: rotating "; L->dump());
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if (MSSAU && VerifyMemorySSA)
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MSSAU->getMemorySSA()->verifyMemorySSA();
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// Find new Loop header. NewHeader is a Header's one and only successor
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// that is inside loop. Header's other successor is outside the
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// loop. Otherwise loop is not suitable for rotation.
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BasicBlock *Exit = BI->getSuccessor(0);
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BasicBlock *NewHeader = BI->getSuccessor(1);
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if (L->contains(Exit))
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std::swap(Exit, NewHeader);
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assert(NewHeader && "Unable to determine new loop header");
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assert(L->contains(NewHeader) && !L->contains(Exit) &&
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"Unable to determine loop header and exit blocks");
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// This code assumes that the new header has exactly one predecessor.
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// Remove any single-entry PHI nodes in it.
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assert(NewHeader->getSinglePredecessor() &&
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"New header doesn't have one pred!");
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FoldSingleEntryPHINodes(NewHeader);
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// Begin by walking OrigHeader and populating ValueMap with an entry for
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// each Instruction.
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BasicBlock::iterator I = OrigHeader->begin(), E = OrigHeader->end();
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ValueToValueMapTy ValueMap, ValueMapMSSA;
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// For PHI nodes, the value available in OldPreHeader is just the
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// incoming value from OldPreHeader.
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for (; PHINode *PN = dyn_cast<PHINode>(I); ++I)
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InsertNewValueIntoMap(ValueMap, PN,
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PN->getIncomingValueForBlock(OrigPreheader));
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// For the rest of the instructions, either hoist to the OrigPreheader if
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// possible or create a clone in the OldPreHeader if not.
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Instruction *LoopEntryBranch = OrigPreheader->getTerminator();
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// Record all debug intrinsics preceding LoopEntryBranch to avoid duplication.
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using DbgIntrinsicHash =
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std::pair<std::pair<Value *, DILocalVariable *>, DIExpression *>;
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auto makeHash = [](DbgVariableIntrinsic *D) -> DbgIntrinsicHash {
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return {{D->getVariableLocation(), D->getVariable()}, D->getExpression()};
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};
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SmallDenseSet<DbgIntrinsicHash, 8> DbgIntrinsics;
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for (auto I = std::next(OrigPreheader->rbegin()), E = OrigPreheader->rend();
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I != E; ++I) {
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if (auto *DII = dyn_cast<DbgVariableIntrinsic>(&*I))
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DbgIntrinsics.insert(makeHash(DII));
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else
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break;
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}
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while (I != E) {
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Instruction *Inst = &*I++;
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// If the instruction's operands are invariant and it doesn't read or write
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// memory, then it is safe to hoist. Doing this doesn't change the order of
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// execution in the preheader, but does prevent the instruction from
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// executing in each iteration of the loop. This means it is safe to hoist
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// something that might trap, but isn't safe to hoist something that reads
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// memory (without proving that the loop doesn't write).
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if (L->hasLoopInvariantOperands(Inst) && !Inst->mayReadFromMemory() &&
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!Inst->mayWriteToMemory() && !Inst->isTerminator() &&
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!isa<DbgInfoIntrinsic>(Inst) && !isa<AllocaInst>(Inst)) {
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Inst->moveBefore(LoopEntryBranch);
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continue;
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}
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// Otherwise, create a duplicate of the instruction.
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Instruction *C = Inst->clone();
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// Eagerly remap the operands of the instruction.
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RemapInstruction(C, ValueMap,
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RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
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// Avoid inserting the same intrinsic twice.
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if (auto *DII = dyn_cast<DbgVariableIntrinsic>(C))
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if (DbgIntrinsics.count(makeHash(DII))) {
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C->deleteValue();
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continue;
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}
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// With the operands remapped, see if the instruction constant folds or is
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// otherwise simplifyable. This commonly occurs because the entry from PHI
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// nodes allows icmps and other instructions to fold.
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Value *V = SimplifyInstruction(C, SQ);
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if (V && LI->replacementPreservesLCSSAForm(C, V)) {
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// If so, then delete the temporary instruction and stick the folded value
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// in the map.
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InsertNewValueIntoMap(ValueMap, Inst, V);
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if (!C->mayHaveSideEffects()) {
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C->deleteValue();
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C = nullptr;
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}
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} else {
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InsertNewValueIntoMap(ValueMap, Inst, C);
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}
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if (C) {
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// Otherwise, stick the new instruction into the new block!
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C->setName(Inst->getName());
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C->insertBefore(LoopEntryBranch);
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if (auto *II = dyn_cast<IntrinsicInst>(C))
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if (II->getIntrinsicID() == Intrinsic::assume)
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AC->registerAssumption(II);
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// MemorySSA cares whether the cloned instruction was inserted or not, and
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// not whether it can be remapped to a simplified value.
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if (MSSAU)
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InsertNewValueIntoMap(ValueMapMSSA, Inst, C);
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}
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}
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// Along with all the other instructions, we just cloned OrigHeader's
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// terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's
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// successors by duplicating their incoming values for OrigHeader.
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for (BasicBlock *SuccBB : successors(OrigHeader))
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for (BasicBlock::iterator BI = SuccBB->begin();
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|
PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
|
|
PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreheader);
|
|
|
|
// Now that OrigPreHeader has a clone of OrigHeader's terminator, remove
|
|
// OrigPreHeader's old terminator (the original branch into the loop), and
|
|
// remove the corresponding incoming values from the PHI nodes in OrigHeader.
|
|
LoopEntryBranch->eraseFromParent();
|
|
|
|
// Update MemorySSA before the rewrite call below changes the 1:1
|
|
// instruction:cloned_instruction_or_value mapping.
|
|
if (MSSAU) {
|
|
InsertNewValueIntoMap(ValueMapMSSA, OrigHeader, OrigPreheader);
|
|
MSSAU->updateForClonedBlockIntoPred(OrigHeader, OrigPreheader,
|
|
ValueMapMSSA);
|
|
}
|
|
|
|
SmallVector<PHINode*, 2> InsertedPHIs;
|
|
// If there were any uses of instructions in the duplicated block outside the
|
|
// loop, update them, inserting PHI nodes as required
|
|
RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap,
|
|
&InsertedPHIs);
|
|
|
|
// Attach dbg.value intrinsics to the new phis if that phi uses a value that
|
|
// previously had debug metadata attached. This keeps the debug info
|
|
// up-to-date in the loop body.
|
|
if (!InsertedPHIs.empty())
|
|
insertDebugValuesForPHIs(OrigHeader, InsertedPHIs);
|
|
|
|
// NewHeader is now the header of the loop.
|
|
L->moveToHeader(NewHeader);
|
|
assert(L->getHeader() == NewHeader && "Latch block is our new header");
|
|
|
|
// Inform DT about changes to the CFG.
|
|
if (DT) {
|
|
// The OrigPreheader branches to the NewHeader and Exit now. Then, inform
|
|
// the DT about the removed edge to the OrigHeader (that got removed).
|
|
SmallVector<DominatorTree::UpdateType, 3> Updates;
|
|
Updates.push_back({DominatorTree::Insert, OrigPreheader, Exit});
|
|
Updates.push_back({DominatorTree::Insert, OrigPreheader, NewHeader});
|
|
Updates.push_back({DominatorTree::Delete, OrigPreheader, OrigHeader});
|
|
DT->applyUpdates(Updates);
|
|
|
|
if (MSSAU) {
|
|
MSSAU->applyUpdates(Updates, *DT);
|
|
if (VerifyMemorySSA)
|
|
MSSAU->getMemorySSA()->verifyMemorySSA();
|
|
}
|
|
}
|
|
|
|
// At this point, we've finished our major CFG changes. As part of cloning
|
|
// the loop into the preheader we've simplified instructions and the
|
|
// duplicated conditional branch may now be branching on a constant. If it is
|
|
// branching on a constant and if that constant means that we enter the loop,
|
|
// then we fold away the cond branch to an uncond branch. This simplifies the
|
|
// loop in cases important for nested loops, and it also means we don't have
|
|
// to split as many edges.
|
|
BranchInst *PHBI = cast<BranchInst>(OrigPreheader->getTerminator());
|
|
assert(PHBI->isConditional() && "Should be clone of BI condbr!");
|
|
if (!isa<ConstantInt>(PHBI->getCondition()) ||
|
|
PHBI->getSuccessor(cast<ConstantInt>(PHBI->getCondition())->isZero()) !=
|
|
NewHeader) {
|
|
// The conditional branch can't be folded, handle the general case.
|
|
// Split edges as necessary to preserve LoopSimplify form.
|
|
|
|
// Right now OrigPreHeader has two successors, NewHeader and ExitBlock, and
|
|
// thus is not a preheader anymore.
|
|
// Split the edge to form a real preheader.
|
|
BasicBlock *NewPH = SplitCriticalEdge(
|
|
OrigPreheader, NewHeader,
|
|
CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA());
|
|
NewPH->setName(NewHeader->getName() + ".lr.ph");
|
|
|
|
// Preserve canonical loop form, which means that 'Exit' should have only
|
|
// one predecessor. Note that Exit could be an exit block for multiple
|
|
// nested loops, causing both of the edges to now be critical and need to
|
|
// be split.
|
|
SmallVector<BasicBlock *, 4> ExitPreds(pred_begin(Exit), pred_end(Exit));
|
|
bool SplitLatchEdge = false;
|
|
for (BasicBlock *ExitPred : ExitPreds) {
|
|
// We only need to split loop exit edges.
|
|
Loop *PredLoop = LI->getLoopFor(ExitPred);
|
|
if (!PredLoop || PredLoop->contains(Exit) ||
|
|
ExitPred->getTerminator()->isIndirectTerminator())
|
|
continue;
|
|
SplitLatchEdge |= L->getLoopLatch() == ExitPred;
|
|
BasicBlock *ExitSplit = SplitCriticalEdge(
|
|
ExitPred, Exit,
|
|
CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA());
|
|
ExitSplit->moveBefore(Exit);
|
|
}
|
|
assert(SplitLatchEdge &&
|
|
"Despite splitting all preds, failed to split latch exit?");
|
|
} else {
|
|
// We can fold the conditional branch in the preheader, this makes things
|
|
// simpler. The first step is to remove the extra edge to the Exit block.
|
|
Exit->removePredecessor(OrigPreheader, true /*preserve LCSSA*/);
|
|
BranchInst *NewBI = BranchInst::Create(NewHeader, PHBI);
|
|
NewBI->setDebugLoc(PHBI->getDebugLoc());
|
|
PHBI->eraseFromParent();
|
|
|
|
// With our CFG finalized, update DomTree if it is available.
|
|
if (DT) DT->deleteEdge(OrigPreheader, Exit);
|
|
|
|
// Update MSSA too, if available.
|
|
if (MSSAU)
|
|
MSSAU->removeEdge(OrigPreheader, Exit);
|
|
}
|
|
|
|
assert(L->getLoopPreheader() && "Invalid loop preheader after loop rotation");
|
|
assert(L->getLoopLatch() && "Invalid loop latch after loop rotation");
|
|
|
|
if (MSSAU && VerifyMemorySSA)
|
|
MSSAU->getMemorySSA()->verifyMemorySSA();
|
|
|
|
// Now that the CFG and DomTree are in a consistent state again, try to merge
|
|
// the OrigHeader block into OrigLatch. This will succeed if they are
|
|
// connected by an unconditional branch. This is just a cleanup so the
|
|
// emitted code isn't too gross in this common case.
|
|
DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
|
|
BasicBlock *PredBB = OrigHeader->getUniquePredecessor();
|
|
bool DidMerge = MergeBlockIntoPredecessor(OrigHeader, &DTU, LI, MSSAU);
|
|
if (DidMerge)
|
|
RemoveRedundantDbgInstrs(PredBB);
|
|
|
|
if (MSSAU && VerifyMemorySSA)
|
|
MSSAU->getMemorySSA()->verifyMemorySSA();
|
|
|
|
LLVM_DEBUG(dbgs() << "LoopRotation: into "; L->dump());
|
|
|
|
++NumRotated;
|
|
|
|
Rotated = true;
|
|
SimplifiedLatch = false;
|
|
|
|
// Check that new latch is a deoptimizing exit and then repeat rotation if possible.
|
|
// Deoptimizing latch exit is not a generally typical case, so we just loop over.
|
|
// TODO: if it becomes a performance bottleneck extend rotation algorithm
|
|
// to handle multiple rotations in one go.
|
|
} while (MultiRotate && canRotateDeoptimizingLatchExit(L));
|
|
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Determine whether the instructions in this range may be safely and cheaply
|
|
/// speculated. This is not an important enough situation to develop complex
|
|
/// heuristics. We handle a single arithmetic instruction along with any type
|
|
/// conversions.
|
|
static bool shouldSpeculateInstrs(BasicBlock::iterator Begin,
|
|
BasicBlock::iterator End, Loop *L) {
|
|
bool seenIncrement = false;
|
|
bool MultiExitLoop = false;
|
|
|
|
if (!L->getExitingBlock())
|
|
MultiExitLoop = true;
|
|
|
|
for (BasicBlock::iterator I = Begin; I != End; ++I) {
|
|
|
|
if (!isSafeToSpeculativelyExecute(&*I))
|
|
return false;
|
|
|
|
if (isa<DbgInfoIntrinsic>(I))
|
|
continue;
|
|
|
|
switch (I->getOpcode()) {
|
|
default:
|
|
return false;
|
|
case Instruction::GetElementPtr:
|
|
// GEPs are cheap if all indices are constant.
|
|
if (!cast<GEPOperator>(I)->hasAllConstantIndices())
|
|
return false;
|
|
// fall-thru to increment case
|
|
LLVM_FALLTHROUGH;
|
|
case Instruction::Add:
|
|
case Instruction::Sub:
|
|
case Instruction::And:
|
|
case Instruction::Or:
|
|
case Instruction::Xor:
|
|
case Instruction::Shl:
|
|
case Instruction::LShr:
|
|
case Instruction::AShr: {
|
|
Value *IVOpnd =
|
|
!isa<Constant>(I->getOperand(0))
|
|
? I->getOperand(0)
|
|
: !isa<Constant>(I->getOperand(1)) ? I->getOperand(1) : nullptr;
|
|
if (!IVOpnd)
|
|
return false;
|
|
|
|
// If increment operand is used outside of the loop, this speculation
|
|
// could cause extra live range interference.
|
|
if (MultiExitLoop) {
|
|
for (User *UseI : IVOpnd->users()) {
|
|
auto *UserInst = cast<Instruction>(UseI);
|
|
if (!L->contains(UserInst))
|
|
return false;
|
|
}
|
|
}
|
|
|
|
if (seenIncrement)
|
|
return false;
|
|
seenIncrement = true;
|
|
break;
|
|
}
|
|
case Instruction::Trunc:
|
|
case Instruction::ZExt:
|
|
case Instruction::SExt:
|
|
// ignore type conversions
|
|
break;
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// Fold the loop tail into the loop exit by speculating the loop tail
|
|
/// instructions. Typically, this is a single post-increment. In the case of a
|
|
/// simple 2-block loop, hoisting the increment can be much better than
|
|
/// duplicating the entire loop header. In the case of loops with early exits,
|
|
/// rotation will not work anyway, but simplifyLoopLatch will put the loop in
|
|
/// canonical form so downstream passes can handle it.
|
|
///
|
|
/// I don't believe this invalidates SCEV.
|
|
bool LoopRotate::simplifyLoopLatch(Loop *L) {
|
|
BasicBlock *Latch = L->getLoopLatch();
|
|
if (!Latch || Latch->hasAddressTaken())
|
|
return false;
|
|
|
|
BranchInst *Jmp = dyn_cast<BranchInst>(Latch->getTerminator());
|
|
if (!Jmp || !Jmp->isUnconditional())
|
|
return false;
|
|
|
|
BasicBlock *LastExit = Latch->getSinglePredecessor();
|
|
if (!LastExit || !L->isLoopExiting(LastExit))
|
|
return false;
|
|
|
|
BranchInst *BI = dyn_cast<BranchInst>(LastExit->getTerminator());
|
|
if (!BI)
|
|
return false;
|
|
|
|
if (!shouldSpeculateInstrs(Latch->begin(), Jmp->getIterator(), L))
|
|
return false;
|
|
|
|
LLVM_DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into "
|
|
<< LastExit->getName() << "\n");
|
|
|
|
DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
|
|
MergeBlockIntoPredecessor(Latch, &DTU, LI, MSSAU, nullptr,
|
|
/*PredecessorWithTwoSuccessors=*/true);
|
|
|
|
if (MSSAU && VerifyMemorySSA)
|
|
MSSAU->getMemorySSA()->verifyMemorySSA();
|
|
|
|
return true;
|
|
}
|
|
|
|
/// Rotate \c L, and return true if any modification was made.
|
|
bool LoopRotate::processLoop(Loop *L) {
|
|
// Save the loop metadata.
|
|
MDNode *LoopMD = L->getLoopID();
|
|
|
|
bool SimplifiedLatch = false;
|
|
|
|
// Simplify the loop latch before attempting to rotate the header
|
|
// upward. Rotation may not be needed if the loop tail can be folded into the
|
|
// loop exit.
|
|
if (!RotationOnly)
|
|
SimplifiedLatch = simplifyLoopLatch(L);
|
|
|
|
bool MadeChange = rotateLoop(L, SimplifiedLatch);
|
|
assert((!MadeChange || L->isLoopExiting(L->getLoopLatch())) &&
|
|
"Loop latch should be exiting after loop-rotate.");
|
|
|
|
// Restore the loop metadata.
|
|
// NB! We presume LoopRotation DOESN'T ADD its own metadata.
|
|
if ((MadeChange || SimplifiedLatch) && LoopMD)
|
|
L->setLoopID(LoopMD);
|
|
|
|
return MadeChange || SimplifiedLatch;
|
|
}
|
|
|
|
|
|
/// The utility to convert a loop into a loop with bottom test.
|
|
bool llvm::LoopRotation(Loop *L, LoopInfo *LI, const TargetTransformInfo *TTI,
|
|
AssumptionCache *AC, DominatorTree *DT,
|
|
ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
|
|
const SimplifyQuery &SQ, bool RotationOnly = true,
|
|
unsigned Threshold = unsigned(-1),
|
|
bool IsUtilMode = true) {
|
|
LoopRotate LR(Threshold, LI, TTI, AC, DT, SE, MSSAU, SQ, RotationOnly,
|
|
IsUtilMode);
|
|
return LR.processLoop(L);
|
|
}
|