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692 lines
24 KiB
692 lines
24 KiB
//===- GuardWidening.cpp - ---- Guard widening ----------------------------===//
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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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// This file implements the guard widening pass. The semantics of the
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// @llvm.experimental.guard intrinsic lets LLVM transform it so that it fails
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// more often that it did before the transform. This optimization is called
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// "widening" and can be used hoist and common runtime checks in situations like
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// these:
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//
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// %cmp0 = 7 u< Length
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// call @llvm.experimental.guard(i1 %cmp0) [ "deopt"(...) ]
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// call @unknown_side_effects()
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// %cmp1 = 9 u< Length
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// call @llvm.experimental.guard(i1 %cmp1) [ "deopt"(...) ]
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// ...
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//
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// =>
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//
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// %cmp0 = 9 u< Length
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// call @llvm.experimental.guard(i1 %cmp0) [ "deopt"(...) ]
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// call @unknown_side_effects()
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// ...
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//
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// If %cmp0 is false, @llvm.experimental.guard will "deoptimize" back to a
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// generic implementation of the same function, which will have the correct
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// semantics from that point onward. It is always _legal_ to deoptimize (so
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// replacing %cmp0 with false is "correct"), though it may not always be
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// profitable to do so.
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//
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// NB! This pass is a work in progress. It hasn't been tuned to be "production
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// ready" yet. It is known to have quadriatic running time and will not scale
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// to large numbers of guards
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar/GuardWidening.h"
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#include "llvm/Pass.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/PostDominators.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/PatternMatch.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Transforms/Scalar.h"
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using namespace llvm;
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#define DEBUG_TYPE "guard-widening"
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namespace {
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class GuardWideningImpl {
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DominatorTree &DT;
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PostDominatorTree &PDT;
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LoopInfo &LI;
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/// The set of guards whose conditions have been widened into dominating
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/// guards.
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SmallVector<IntrinsicInst *, 16> EliminatedGuards;
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/// The set of guards which have been widened to include conditions to other
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/// guards.
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DenseSet<IntrinsicInst *> WidenedGuards;
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/// Try to eliminate guard \p Guard by widening it into an earlier dominating
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/// guard. \p DFSI is the DFS iterator on the dominator tree that is
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/// currently visiting the block containing \p Guard, and \p GuardsPerBlock
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/// maps BasicBlocks to the set of guards seen in that block.
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bool eliminateGuardViaWidening(
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IntrinsicInst *Guard, const df_iterator<DomTreeNode *> &DFSI,
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const DenseMap<BasicBlock *, SmallVector<IntrinsicInst *, 8>> &
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GuardsPerBlock);
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/// Used to keep track of which widening potential is more effective.
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enum WideningScore {
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/// Don't widen.
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WS_IllegalOrNegative,
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/// Widening is performance neutral as far as the cycles spent in check
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/// conditions goes (but can still help, e.g., code layout, having less
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/// deopt state).
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WS_Neutral,
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/// Widening is profitable.
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WS_Positive,
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/// Widening is very profitable. Not significantly different from \c
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/// WS_Positive, except by the order.
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WS_VeryPositive
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};
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static StringRef scoreTypeToString(WideningScore WS);
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/// Compute the score for widening the condition in \p DominatedGuard
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/// (contained in \p DominatedGuardLoop) into \p DominatingGuard (contained in
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/// \p DominatingGuardLoop).
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WideningScore computeWideningScore(IntrinsicInst *DominatedGuard,
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Loop *DominatedGuardLoop,
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IntrinsicInst *DominatingGuard,
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Loop *DominatingGuardLoop);
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/// Helper to check if \p V can be hoisted to \p InsertPos.
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bool isAvailableAt(Value *V, Instruction *InsertPos) {
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SmallPtrSet<Instruction *, 8> Visited;
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return isAvailableAt(V, InsertPos, Visited);
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}
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bool isAvailableAt(Value *V, Instruction *InsertPos,
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SmallPtrSetImpl<Instruction *> &Visited);
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/// Helper to hoist \p V to \p InsertPos. Guaranteed to succeed if \c
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/// isAvailableAt returned true.
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void makeAvailableAt(Value *V, Instruction *InsertPos);
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/// Common helper used by \c widenGuard and \c isWideningCondProfitable. Try
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/// to generate an expression computing the logical AND of \p Cond0 and \p
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/// Cond1. Return true if the expression computing the AND is only as
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/// expensive as computing one of the two. If \p InsertPt is true then
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/// actually generate the resulting expression, make it available at \p
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/// InsertPt and return it in \p Result (else no change to the IR is made).
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bool widenCondCommon(Value *Cond0, Value *Cond1, Instruction *InsertPt,
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Value *&Result);
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/// Represents a range check of the form \c Base + \c Offset u< \c Length,
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/// with the constraint that \c Length is not negative. \c CheckInst is the
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/// pre-existing instruction in the IR that computes the result of this range
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/// check.
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class RangeCheck {
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Value *Base;
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ConstantInt *Offset;
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Value *Length;
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ICmpInst *CheckInst;
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public:
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explicit RangeCheck(Value *Base, ConstantInt *Offset, Value *Length,
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ICmpInst *CheckInst)
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: Base(Base), Offset(Offset), Length(Length), CheckInst(CheckInst) {}
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void setBase(Value *NewBase) { Base = NewBase; }
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void setOffset(ConstantInt *NewOffset) { Offset = NewOffset; }
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Value *getBase() const { return Base; }
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ConstantInt *getOffset() const { return Offset; }
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const APInt &getOffsetValue() const { return getOffset()->getValue(); }
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Value *getLength() const { return Length; };
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ICmpInst *getCheckInst() const { return CheckInst; }
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void print(raw_ostream &OS, bool PrintTypes = false) {
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OS << "Base: ";
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Base->printAsOperand(OS, PrintTypes);
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OS << " Offset: ";
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Offset->printAsOperand(OS, PrintTypes);
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OS << " Length: ";
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Length->printAsOperand(OS, PrintTypes);
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}
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LLVM_DUMP_METHOD void dump() {
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print(dbgs());
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dbgs() << "\n";
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}
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};
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/// Parse \p CheckCond into a conjunction (logical-and) of range checks; and
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/// append them to \p Checks. Returns true on success, may clobber \c Checks
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/// on failure.
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bool parseRangeChecks(Value *CheckCond, SmallVectorImpl<RangeCheck> &Checks) {
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SmallPtrSet<Value *, 8> Visited;
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return parseRangeChecks(CheckCond, Checks, Visited);
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}
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bool parseRangeChecks(Value *CheckCond, SmallVectorImpl<RangeCheck> &Checks,
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SmallPtrSetImpl<Value *> &Visited);
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/// Combine the checks in \p Checks into a smaller set of checks and append
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/// them into \p CombinedChecks. Return true on success (i.e. all of checks
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/// in \p Checks were combined into \p CombinedChecks). Clobbers \p Checks
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/// and \p CombinedChecks on success and on failure.
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bool combineRangeChecks(SmallVectorImpl<RangeCheck> &Checks,
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SmallVectorImpl<RangeCheck> &CombinedChecks);
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/// Can we compute the logical AND of \p Cond0 and \p Cond1 for the price of
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/// computing only one of the two expressions?
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bool isWideningCondProfitable(Value *Cond0, Value *Cond1) {
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Value *ResultUnused;
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return widenCondCommon(Cond0, Cond1, /*InsertPt=*/nullptr, ResultUnused);
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}
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/// Widen \p ToWiden to fail if \p NewCondition is false (in addition to
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/// whatever it is already checking).
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void widenGuard(IntrinsicInst *ToWiden, Value *NewCondition) {
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Value *Result;
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widenCondCommon(ToWiden->getArgOperand(0), NewCondition, ToWiden, Result);
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ToWiden->setArgOperand(0, Result);
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}
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public:
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explicit GuardWideningImpl(DominatorTree &DT, PostDominatorTree &PDT,
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LoopInfo &LI)
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: DT(DT), PDT(PDT), LI(LI) {}
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/// The entry point for this pass.
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bool run();
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};
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struct GuardWideningLegacyPass : public FunctionPass {
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static char ID;
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GuardWideningPass Impl;
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GuardWideningLegacyPass() : FunctionPass(ID) {
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initializeGuardWideningLegacyPassPass(*PassRegistry::getPassRegistry());
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}
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bool runOnFunction(Function &F) override {
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if (skipFunction(F))
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return false;
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return GuardWideningImpl(
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getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
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getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree(),
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getAnalysis<LoopInfoWrapperPass>().getLoopInfo()).run();
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}
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.setPreservesCFG();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<PostDominatorTreeWrapperPass>();
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AU.addRequired<LoopInfoWrapperPass>();
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}
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};
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}
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bool GuardWideningImpl::run() {
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using namespace llvm::PatternMatch;
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DenseMap<BasicBlock *, SmallVector<IntrinsicInst *, 8>> GuardsInBlock;
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bool Changed = false;
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for (auto DFI = df_begin(DT.getRootNode()), DFE = df_end(DT.getRootNode());
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DFI != DFE; ++DFI) {
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auto *BB = (*DFI)->getBlock();
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auto &CurrentList = GuardsInBlock[BB];
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for (auto &I : *BB)
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if (match(&I, m_Intrinsic<Intrinsic::experimental_guard>()))
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CurrentList.push_back(cast<IntrinsicInst>(&I));
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for (auto *II : CurrentList)
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Changed |= eliminateGuardViaWidening(II, DFI, GuardsInBlock);
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}
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for (auto *II : EliminatedGuards)
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if (!WidenedGuards.count(II))
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II->eraseFromParent();
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return Changed;
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}
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bool GuardWideningImpl::eliminateGuardViaWidening(
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IntrinsicInst *GuardInst, const df_iterator<DomTreeNode *> &DFSI,
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const DenseMap<BasicBlock *, SmallVector<IntrinsicInst *, 8>> &
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GuardsInBlock) {
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IntrinsicInst *BestSoFar = nullptr;
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auto BestScoreSoFar = WS_IllegalOrNegative;
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auto *GuardInstLoop = LI.getLoopFor(GuardInst->getParent());
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// In the set of dominating guards, find the one we can merge GuardInst with
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// for the most profit.
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for (unsigned i = 0, e = DFSI.getPathLength(); i != e; ++i) {
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auto *CurBB = DFSI.getPath(i)->getBlock();
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auto *CurLoop = LI.getLoopFor(CurBB);
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assert(GuardsInBlock.count(CurBB) && "Must have been populated by now!");
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const auto &GuardsInCurBB = GuardsInBlock.find(CurBB)->second;
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auto I = GuardsInCurBB.begin();
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auto E = GuardsInCurBB.end();
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#ifndef NDEBUG
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{
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unsigned Index = 0;
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for (auto &I : *CurBB) {
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if (Index == GuardsInCurBB.size())
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break;
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if (GuardsInCurBB[Index] == &I)
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Index++;
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}
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assert(Index == GuardsInCurBB.size() &&
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"Guards expected to be in order!");
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}
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#endif
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assert((i == (e - 1)) == (GuardInst->getParent() == CurBB) && "Bad DFS?");
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if (i == (e - 1)) {
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// Corner case: make sure we're only looking at guards strictly dominating
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// GuardInst when visiting GuardInst->getParent().
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auto NewEnd = std::find(I, E, GuardInst);
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assert(NewEnd != E && "GuardInst not in its own block?");
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E = NewEnd;
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}
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for (auto *Candidate : make_range(I, E)) {
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auto Score =
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computeWideningScore(GuardInst, GuardInstLoop, Candidate, CurLoop);
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DEBUG(dbgs() << "Score between " << *GuardInst->getArgOperand(0)
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<< " and " << *Candidate->getArgOperand(0) << " is "
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<< scoreTypeToString(Score) << "\n");
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if (Score > BestScoreSoFar) {
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BestScoreSoFar = Score;
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BestSoFar = Candidate;
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}
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}
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}
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if (BestScoreSoFar == WS_IllegalOrNegative) {
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DEBUG(dbgs() << "Did not eliminate guard " << *GuardInst << "\n");
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return false;
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}
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assert(BestSoFar != GuardInst && "Should have never visited same guard!");
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assert(DT.dominates(BestSoFar, GuardInst) && "Should be!");
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DEBUG(dbgs() << "Widening " << *GuardInst << " into " << *BestSoFar
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<< " with score " << scoreTypeToString(BestScoreSoFar) << "\n");
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widenGuard(BestSoFar, GuardInst->getArgOperand(0));
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GuardInst->setArgOperand(0, ConstantInt::getTrue(GuardInst->getContext()));
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EliminatedGuards.push_back(GuardInst);
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WidenedGuards.insert(BestSoFar);
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return true;
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}
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GuardWideningImpl::WideningScore GuardWideningImpl::computeWideningScore(
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IntrinsicInst *DominatedGuard, Loop *DominatedGuardLoop,
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IntrinsicInst *DominatingGuard, Loop *DominatingGuardLoop) {
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bool HoistingOutOfLoop = false;
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if (DominatingGuardLoop != DominatedGuardLoop) {
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if (DominatingGuardLoop &&
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!DominatingGuardLoop->contains(DominatedGuardLoop))
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return WS_IllegalOrNegative;
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HoistingOutOfLoop = true;
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}
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if (!isAvailableAt(DominatedGuard->getArgOperand(0), DominatingGuard))
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return WS_IllegalOrNegative;
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bool HoistingOutOfIf =
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!PDT.dominates(DominatedGuard->getParent(), DominatingGuard->getParent());
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if (isWideningCondProfitable(DominatedGuard->getArgOperand(0),
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DominatingGuard->getArgOperand(0)))
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return HoistingOutOfLoop ? WS_VeryPositive : WS_Positive;
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if (HoistingOutOfLoop)
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return WS_Positive;
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return HoistingOutOfIf ? WS_IllegalOrNegative : WS_Neutral;
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}
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bool GuardWideningImpl::isAvailableAt(Value *V, Instruction *Loc,
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SmallPtrSetImpl<Instruction *> &Visited) {
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auto *Inst = dyn_cast<Instruction>(V);
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if (!Inst || DT.dominates(Inst, Loc) || Visited.count(Inst))
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return true;
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if (!isSafeToSpeculativelyExecute(Inst, Loc, &DT) ||
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Inst->mayReadFromMemory())
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return false;
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Visited.insert(Inst);
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// We only want to go _up_ the dominance chain when recursing.
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assert(!isa<PHINode>(Loc) &&
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"PHIs should return false for isSafeToSpeculativelyExecute");
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assert(DT.isReachableFromEntry(Inst->getParent()) &&
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"We did a DFS from the block entry!");
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return all_of(Inst->operands(),
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[&](Value *Op) { return isAvailableAt(Op, Loc, Visited); });
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}
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void GuardWideningImpl::makeAvailableAt(Value *V, Instruction *Loc) {
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auto *Inst = dyn_cast<Instruction>(V);
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if (!Inst || DT.dominates(Inst, Loc))
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return;
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assert(isSafeToSpeculativelyExecute(Inst, Loc, &DT) &&
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!Inst->mayReadFromMemory() && "Should've checked with isAvailableAt!");
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for (Value *Op : Inst->operands())
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makeAvailableAt(Op, Loc);
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Inst->moveBefore(Loc);
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}
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bool GuardWideningImpl::widenCondCommon(Value *Cond0, Value *Cond1,
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Instruction *InsertPt, Value *&Result) {
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using namespace llvm::PatternMatch;
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{
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// L >u C0 && L >u C1 -> L >u max(C0, C1)
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ConstantInt *RHS0, *RHS1;
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Value *LHS;
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ICmpInst::Predicate Pred0, Pred1;
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if (match(Cond0, m_ICmp(Pred0, m_Value(LHS), m_ConstantInt(RHS0))) &&
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match(Cond1, m_ICmp(Pred1, m_Specific(LHS), m_ConstantInt(RHS1)))) {
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ConstantRange CR0 =
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ConstantRange::makeExactICmpRegion(Pred0, RHS0->getValue());
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ConstantRange CR1 =
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ConstantRange::makeExactICmpRegion(Pred1, RHS1->getValue());
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// SubsetIntersect is a subset of the actual mathematical intersection of
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// CR0 and CR1, while SupersetIntersect is a superset of the actual
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// mathematical intersection. If these two ConstantRanges are equal, then
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// we know we were able to represent the actual mathematical intersection
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// of CR0 and CR1, and can use the same to generate an icmp instruction.
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//
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// Given what we're doing here and the semantics of guards, it would
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// actually be correct to just use SubsetIntersect, but that may be too
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// aggressive in cases we care about.
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auto SubsetIntersect = CR0.inverse().unionWith(CR1.inverse()).inverse();
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auto SupersetIntersect = CR0.intersectWith(CR1);
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APInt NewRHSAP;
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CmpInst::Predicate Pred;
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if (SubsetIntersect == SupersetIntersect &&
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SubsetIntersect.getEquivalentICmp(Pred, NewRHSAP)) {
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if (InsertPt) {
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ConstantInt *NewRHS = ConstantInt::get(Cond0->getContext(), NewRHSAP);
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Result = new ICmpInst(InsertPt, Pred, LHS, NewRHS, "wide.chk");
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}
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return true;
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}
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}
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}
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{
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SmallVector<GuardWideningImpl::RangeCheck, 4> Checks, CombinedChecks;
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if (parseRangeChecks(Cond0, Checks) && parseRangeChecks(Cond1, Checks) &&
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combineRangeChecks(Checks, CombinedChecks)) {
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if (InsertPt) {
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Result = nullptr;
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for (auto &RC : CombinedChecks) {
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makeAvailableAt(RC.getCheckInst(), InsertPt);
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if (Result)
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Result = BinaryOperator::CreateAnd(RC.getCheckInst(), Result, "",
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InsertPt);
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else
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Result = RC.getCheckInst();
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}
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Result->setName("wide.chk");
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}
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return true;
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}
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}
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// Base case -- just logical-and the two conditions together.
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if (InsertPt) {
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makeAvailableAt(Cond0, InsertPt);
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makeAvailableAt(Cond1, InsertPt);
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Result = BinaryOperator::CreateAnd(Cond0, Cond1, "wide.chk", InsertPt);
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}
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// We were not able to compute Cond0 AND Cond1 for the price of one.
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return false;
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}
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bool GuardWideningImpl::parseRangeChecks(
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Value *CheckCond, SmallVectorImpl<GuardWideningImpl::RangeCheck> &Checks,
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SmallPtrSetImpl<Value *> &Visited) {
|
|
if (!Visited.insert(CheckCond).second)
|
|
return true;
|
|
|
|
using namespace llvm::PatternMatch;
|
|
|
|
{
|
|
Value *AndLHS, *AndRHS;
|
|
if (match(CheckCond, m_And(m_Value(AndLHS), m_Value(AndRHS))))
|
|
return parseRangeChecks(AndLHS, Checks) &&
|
|
parseRangeChecks(AndRHS, Checks);
|
|
}
|
|
|
|
auto *IC = dyn_cast<ICmpInst>(CheckCond);
|
|
if (!IC || !IC->getOperand(0)->getType()->isIntegerTy() ||
|
|
(IC->getPredicate() != ICmpInst::ICMP_ULT &&
|
|
IC->getPredicate() != ICmpInst::ICMP_UGT))
|
|
return false;
|
|
|
|
Value *CmpLHS = IC->getOperand(0), *CmpRHS = IC->getOperand(1);
|
|
if (IC->getPredicate() == ICmpInst::ICMP_UGT)
|
|
std::swap(CmpLHS, CmpRHS);
|
|
|
|
auto &DL = IC->getModule()->getDataLayout();
|
|
|
|
GuardWideningImpl::RangeCheck Check(
|
|
CmpLHS, cast<ConstantInt>(ConstantInt::getNullValue(CmpRHS->getType())),
|
|
CmpRHS, IC);
|
|
|
|
if (!isKnownNonNegative(Check.getLength(), DL))
|
|
return false;
|
|
|
|
// What we have in \c Check now is a correct interpretation of \p CheckCond.
|
|
// Try to see if we can move some constant offsets into the \c Offset field.
|
|
|
|
bool Changed;
|
|
auto &Ctx = CheckCond->getContext();
|
|
|
|
do {
|
|
Value *OpLHS;
|
|
ConstantInt *OpRHS;
|
|
Changed = false;
|
|
|
|
#ifndef NDEBUG
|
|
auto *BaseInst = dyn_cast<Instruction>(Check.getBase());
|
|
assert((!BaseInst || DT.isReachableFromEntry(BaseInst->getParent())) &&
|
|
"Unreachable instruction?");
|
|
#endif
|
|
|
|
if (match(Check.getBase(), m_Add(m_Value(OpLHS), m_ConstantInt(OpRHS)))) {
|
|
Check.setBase(OpLHS);
|
|
APInt NewOffset = Check.getOffsetValue() + OpRHS->getValue();
|
|
Check.setOffset(ConstantInt::get(Ctx, NewOffset));
|
|
Changed = true;
|
|
} else if (match(Check.getBase(),
|
|
m_Or(m_Value(OpLHS), m_ConstantInt(OpRHS)))) {
|
|
unsigned BitWidth = OpLHS->getType()->getScalarSizeInBits();
|
|
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
|
|
computeKnownBits(OpLHS, KnownZero, KnownOne, DL);
|
|
if ((OpRHS->getValue() & KnownZero) == OpRHS->getValue()) {
|
|
Check.setBase(OpLHS);
|
|
APInt NewOffset = Check.getOffsetValue() + OpRHS->getValue();
|
|
Check.setOffset(ConstantInt::get(Ctx, NewOffset));
|
|
Changed = true;
|
|
}
|
|
}
|
|
} while (Changed);
|
|
|
|
Checks.push_back(Check);
|
|
return true;
|
|
}
|
|
|
|
bool GuardWideningImpl::combineRangeChecks(
|
|
SmallVectorImpl<GuardWideningImpl::RangeCheck> &Checks,
|
|
SmallVectorImpl<GuardWideningImpl::RangeCheck> &RangeChecksOut) {
|
|
unsigned OldCount = Checks.size();
|
|
while (!Checks.empty()) {
|
|
// Pick all of the range checks with a specific base and length, and try to
|
|
// merge them.
|
|
Value *CurrentBase = Checks.front().getBase();
|
|
Value *CurrentLength = Checks.front().getLength();
|
|
|
|
SmallVector<GuardWideningImpl::RangeCheck, 3> CurrentChecks;
|
|
|
|
auto IsCurrentCheck = [&](GuardWideningImpl::RangeCheck &RC) {
|
|
return RC.getBase() == CurrentBase && RC.getLength() == CurrentLength;
|
|
};
|
|
|
|
std::copy_if(Checks.begin(), Checks.end(),
|
|
std::back_inserter(CurrentChecks), IsCurrentCheck);
|
|
Checks.erase(remove_if(Checks, IsCurrentCheck), Checks.end());
|
|
|
|
assert(CurrentChecks.size() != 0 && "We know we have at least one!");
|
|
|
|
if (CurrentChecks.size() < 3) {
|
|
RangeChecksOut.insert(RangeChecksOut.end(), CurrentChecks.begin(),
|
|
CurrentChecks.end());
|
|
continue;
|
|
}
|
|
|
|
// CurrentChecks.size() will typically be 3 here, but so far there has been
|
|
// no need to hard-code that fact.
|
|
|
|
std::sort(CurrentChecks.begin(), CurrentChecks.end(),
|
|
[&](const GuardWideningImpl::RangeCheck &LHS,
|
|
const GuardWideningImpl::RangeCheck &RHS) {
|
|
return LHS.getOffsetValue().slt(RHS.getOffsetValue());
|
|
});
|
|
|
|
// Note: std::sort should not invalidate the ChecksStart iterator.
|
|
|
|
ConstantInt *MinOffset = CurrentChecks.front().getOffset(),
|
|
*MaxOffset = CurrentChecks.back().getOffset();
|
|
|
|
unsigned BitWidth = MaxOffset->getValue().getBitWidth();
|
|
if ((MaxOffset->getValue() - MinOffset->getValue())
|
|
.ugt(APInt::getSignedMinValue(BitWidth)))
|
|
return false;
|
|
|
|
APInt MaxDiff = MaxOffset->getValue() - MinOffset->getValue();
|
|
const APInt &HighOffset = MaxOffset->getValue();
|
|
auto OffsetOK = [&](const GuardWideningImpl::RangeCheck &RC) {
|
|
return (HighOffset - RC.getOffsetValue()).ult(MaxDiff);
|
|
};
|
|
|
|
if (MaxDiff.isMinValue() ||
|
|
!std::all_of(std::next(CurrentChecks.begin()), CurrentChecks.end(),
|
|
OffsetOK))
|
|
return false;
|
|
|
|
// We have a series of f+1 checks as:
|
|
//
|
|
// I+k_0 u< L ... Chk_0
|
|
// I_k_1 u< L ... Chk_1
|
|
// ...
|
|
// I_k_f u< L ... Chk_(f+1)
|
|
//
|
|
// with forall i in [0,f): k_f-k_i u< k_f-k_0 ... Precond_0
|
|
// k_f-k_0 u< INT_MIN+k_f ... Precond_1
|
|
// k_f != k_0 ... Precond_2
|
|
//
|
|
// Claim:
|
|
// Chk_0 AND Chk_(f+1) implies all the other checks
|
|
//
|
|
// Informal proof sketch:
|
|
//
|
|
// We will show that the integer range [I+k_0,I+k_f] does not unsigned-wrap
|
|
// (i.e. going from I+k_0 to I+k_f does not cross the -1,0 boundary) and
|
|
// thus I+k_f is the greatest unsigned value in that range.
|
|
//
|
|
// This combined with Ckh_(f+1) shows that everything in that range is u< L.
|
|
// Via Precond_0 we know that all of the indices in Chk_0 through Chk_(f+1)
|
|
// lie in [I+k_0,I+k_f], this proving our claim.
|
|
//
|
|
// To see that [I+k_0,I+k_f] is not a wrapping range, note that there are
|
|
// two possibilities: I+k_0 u< I+k_f or I+k_0 >u I+k_f (they can't be equal
|
|
// since k_0 != k_f). In the former case, [I+k_0,I+k_f] is not a wrapping
|
|
// range by definition, and the latter case is impossible:
|
|
//
|
|
// 0-----I+k_f---I+k_0----L---INT_MAX,INT_MIN------------------(-1)
|
|
// xxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
|
|
//
|
|
// For Chk_0 to succeed, we'd have to have k_f-k_0 (the range highlighted
|
|
// with 'x' above) to be at least >u INT_MIN.
|
|
|
|
RangeChecksOut.emplace_back(CurrentChecks.front());
|
|
RangeChecksOut.emplace_back(CurrentChecks.back());
|
|
}
|
|
|
|
assert(RangeChecksOut.size() <= OldCount && "We pessimized!");
|
|
return RangeChecksOut.size() != OldCount;
|
|
}
|
|
|
|
PreservedAnalyses GuardWideningPass::run(Function &F,
|
|
AnalysisManager<Function> &AM) {
|
|
auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
|
|
auto &LI = AM.getResult<LoopAnalysis>(F);
|
|
auto &PDT = AM.getResult<PostDominatorTreeAnalysis>(F);
|
|
bool Changed = GuardWideningImpl(DT, PDT, LI).run();
|
|
return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
|
|
}
|
|
|
|
StringRef GuardWideningImpl::scoreTypeToString(WideningScore WS) {
|
|
switch (WS) {
|
|
case WS_IllegalOrNegative:
|
|
return "IllegalOrNegative";
|
|
case WS_Neutral:
|
|
return "Neutral";
|
|
case WS_Positive:
|
|
return "Positive";
|
|
case WS_VeryPositive:
|
|
return "VeryPositive";
|
|
}
|
|
|
|
llvm_unreachable("Fully covered switch above!");
|
|
}
|
|
|
|
char GuardWideningLegacyPass::ID = 0;
|
|
|
|
INITIALIZE_PASS_BEGIN(GuardWideningLegacyPass, "guard-widening", "Widen guards",
|
|
false, false)
|
|
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(PostDominatorTreeWrapperPass)
|
|
INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
|
|
INITIALIZE_PASS_END(GuardWideningLegacyPass, "guard-widening", "Widen guards",
|
|
false, false)
|
|
|
|
FunctionPass *llvm::createGuardWideningPass() {
|
|
return new GuardWideningLegacyPass();
|
|
}
|