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Use Alias Analysis to hoist 2 loads from diamond to the common predecessor basic block.
Alias Analysis allows to detect real barriers for load hoisting. Review in http://reviews.llvm.org/D5991 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221091 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Elena Demikhovsky
parent
c821f8794d
commit
01d89eee39
@ -131,7 +131,9 @@ private:
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BasicBlock *getDiamondTail(BasicBlock *BB);
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bool isDiamondHead(BasicBlock *BB);
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// Routines for hoisting loads
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bool isLoadHoistBarrier(Instruction *Inst);
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bool isLoadHoistBarrierInRange(const Instruction& Start,
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const Instruction& End,
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LoadInst* LI);
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LoadInst *canHoistFromBlock(BasicBlock *BB, LoadInst *LI);
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void hoistInstruction(BasicBlock *BB, Instruction *HoistCand,
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Instruction *ElseInst);
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@ -232,27 +234,12 @@ bool MergedLoadStoreMotion::isDiamondHead(BasicBlock *BB) {
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/// being loaded or protect against the load from happening
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/// it is considered a hoist barrier.
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///
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bool MergedLoadStoreMotion::isLoadHoistBarrier(Instruction *Inst) {
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// FIXME: A call with no side effects should not be a barrier.
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// Aren't all such calls covered by mayHaveSideEffects() below?
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// Then this check can be removed.
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if (isa<CallInst>(Inst))
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return true;
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if (isa<TerminatorInst>(Inst))
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return true;
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// FIXME: Conservatively let a store instruction block the load.
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// Use alias analysis instead.
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if (isa<StoreInst>(Inst))
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return true;
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// Note: mayHaveSideEffects covers all instructions that could
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// trigger a change to state. Eg. in-flight stores have to be executed
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// before ordered loads or fences, calls could invoke functions that store
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// data to memory etc.
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if (Inst->mayHaveSideEffects()) {
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return true;
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}
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DEBUG(dbgs() << "No Hoist Barrier\n");
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return false;
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bool MergedLoadStoreMotion::isLoadHoistBarrierInRange(const Instruction& Start,
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const Instruction& End,
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LoadInst* LI) {
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AliasAnalysis::Location Loc = AA->getLocation(LI);
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return AA->canInstructionRangeModify(Start, End, Loc);
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}
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///
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@ -262,33 +249,29 @@ bool MergedLoadStoreMotion::isLoadHoistBarrier(Instruction *Inst) {
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/// and it can be hoisted from \p BB, return that load.
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/// Otherwise return Null.
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///
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LoadInst *MergedLoadStoreMotion::canHoistFromBlock(BasicBlock *BB,
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LoadInst *LI) {
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LoadInst *I = nullptr;
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assert(isa<LoadInst>(LI));
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if (LI->isUsedOutsideOfBlock(LI->getParent()))
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return nullptr;
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LoadInst *MergedLoadStoreMotion::canHoistFromBlock(BasicBlock *BB1,
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LoadInst *Load0) {
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for (BasicBlock::iterator BBI = BB->begin(), BBE = BB->end(); BBI != BBE;
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for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end(); BBI != BBE;
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++BBI) {
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Instruction *Inst = BBI;
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// Only merge and hoist loads when their result in used only in BB
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if (isLoadHoistBarrier(Inst))
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break;
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if (!isa<LoadInst>(Inst))
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continue;
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if (Inst->isUsedOutsideOfBlock(Inst->getParent()))
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if (!isa<LoadInst>(Inst) || Inst->isUsedOutsideOfBlock(BB1))
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continue;
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AliasAnalysis::Location LocLI = AA->getLocation(LI);
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AliasAnalysis::Location LocInst = AA->getLocation((LoadInst *)Inst);
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if (AA->isMustAlias(LocLI, LocInst) && LI->getType() == Inst->getType()) {
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I = (LoadInst *)Inst;
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break;
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LoadInst *Load1 = dyn_cast<LoadInst>(Inst);
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BasicBlock *BB0 = Load0->getParent();
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AliasAnalysis::Location Loc0 = AA->getLocation(Load0);
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AliasAnalysis::Location Loc1 = AA->getLocation(Load1);
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if (AA->isMustAlias(Loc0, Loc1) && Load0->isSameOperationAs(Load1) &&
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!isLoadHoistBarrierInRange(BB1->front(), *Load1, Load1) &&
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!isLoadHoistBarrierInRange(BB0->front(), *Load0, Load0)) {
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return Load1;
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}
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}
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return I;
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return nullptr;
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}
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///
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@ -385,15 +368,10 @@ bool MergedLoadStoreMotion::mergeLoads(BasicBlock *BB) {
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Instruction *I = BBI;
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++BBI;
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if (isLoadHoistBarrier(I))
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break;
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// Only move non-simple (atomic, volatile) loads.
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if (!isa<LoadInst>(I))
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continue;
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LoadInst *L0 = (LoadInst *)I;
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if (!L0->isSimple())
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LoadInst *L0 = dyn_cast<LoadInst>(I);
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if (!L0 || !L0->isSimple() || L0->isUsedOutsideOfBlock(Succ0))
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continue;
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++NLoads;
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64
test/Transforms/InstMerge/ld_hoist1.ll
Normal file
64
test/Transforms/InstMerge/ld_hoist1.ll
Normal file
@ -0,0 +1,64 @@
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; Test load hoist
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; RUN: opt -basicaa -memdep -mldst-motion -S < %s | FileCheck %s
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-pc_linux"
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; Function Attrs: nounwind uwtable
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define float* @foo(i32* noalias nocapture readonly %in, float* noalias %out, i32 %size, i32* nocapture readonly %trigger) {
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entry:
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%cmp11 = icmp eq i32 %size, 0
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br i1 %cmp11, label %for.end, label %for.body.lr.ph
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for.body.lr.ph: ; preds = %entry
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%0 = add i32 %size, -1
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br label %for.body
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; CHECK-LABEL: for.body
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; CHECK: load
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; CHECK: %2 = getelementptr inbounds i32* %in, i64 %indvars.iv
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; CHECK: %3 = load i32* %2, align 4
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for.body: ; preds = %for.body.lr.ph, %for.inc
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%indvars.iv = phi i64 [ 0, %for.body.lr.ph ], [ %indvars.iv.next, %for.inc ]
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%arrayidx = getelementptr inbounds i32* %trigger, i64 %indvars.iv
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%1 = load i32* %arrayidx, align 4
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%cmp1 = icmp sgt i32 %1, 0
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br i1 %cmp1, label %if.then, label %if.else
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; CHECK-LABEL: if.then
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if.then: ; preds = %for.body
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; This load should be hoisted
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%arrayidx3 = getelementptr inbounds i32* %in, i64 %indvars.iv
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%2 = load i32* %arrayidx3, align 4
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%conv = sitofp i32 %2 to float
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%add = fadd float %conv, 5.000000e-01
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%arrayidx5 = getelementptr inbounds float* %out, i64 %indvars.iv
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store float %add, float* %arrayidx5, align 4
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br label %for.inc
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if.else: ; preds = %for.body
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%arrayidx7 = getelementptr inbounds float* %out, i64 %indvars.iv
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%3 = load float* %arrayidx7, align 4
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%div = fdiv float %3, 3.000000e+00
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store float %div, float* %arrayidx7, align 4
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; This load should be hoisted in spite of store
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%arrayidx9 = getelementptr inbounds i32* %in, i64 %indvars.iv
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%4 = load i32* %arrayidx9, align 4
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%conv10 = sitofp i32 %4 to float
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%add13 = fadd float %div, %conv10
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store float %add13, float* %arrayidx7, align 4
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br label %for.inc
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for.inc: ; preds = %if.then, %if.else
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%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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%lftr.wideiv = trunc i64 %indvars.iv to i32
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%exitcond = icmp ne i32 %lftr.wideiv, %0
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br i1 %exitcond, label %for.body, label %for.cond.for.end_crit_edge
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for.cond.for.end_crit_edge: ; preds = %for.inc
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br label %for.end
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for.end: ; preds = %entry, %for.cond.for.end_crit_edge
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ret float* %out
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}
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