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Teach basicaa that memset's modref set is at worst "mod" and never
contains "ref". Enhance DSE to use a modref query instead of a store-specific hack to generalize the "ignore may-alias stores" optimization to handle memset and memcpy. llvm-svn: 120368
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parent
6c0221e3ae
commit
8ec1830a01
lib
test/Transforms/DeadStoreElimination
@ -703,6 +703,8 @@ BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
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if (isNoAlias(Location(Dest, Len), Loc))
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return NoModRef;
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}
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// We know that memset doesn't load anything.
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Min = Mod;
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break;
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case Intrinsic::atomic_cmp_swap:
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case Intrinsic::atomic_swap:
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@ -191,6 +191,7 @@ static bool isStoreAtLeastAsWideAs(Instruction *I1, Instruction *I2,
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I1Size >= I2Size;
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}
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bool DSE::runOnBasicBlock(BasicBlock &BB) {
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MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
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TD = getAnalysisIfAvailable<TargetData>();
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@ -239,7 +240,7 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
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}
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}
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}
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if (!InstDep.isDef()) {
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// If this is a may-aliased store that is clobbering the store value, we
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// can keep searching past it for another must-aliased pointer that stores
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@ -250,12 +251,16 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
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// we can remove the first store to P even though we don't know if P and Q
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// alias.
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if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
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AliasAnalysis::Location Loc =
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getAnalysis<AliasAnalysis>().getLocation(SI);
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while (InstDep.isClobber() && isa<StoreInst>(InstDep.getInst()) &&
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InstDep.getInst() != &BB.front())
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InstDep = MD.getPointerDependencyFrom(Loc, false, InstDep.getInst(),
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&BB);
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AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
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AliasAnalysis::Location Loc = AA.getLocation(SI);
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while (InstDep.isClobber() && InstDep.getInst() != &BB.front()) {
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// Can't look past this instruction if it might read 'Loc'.
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if (AA.getModRefInfo(InstDep.getInst(), Loc) & AliasAnalysis::Ref)
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break;
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InstDep = MD.getPointerDependencyFrom(Loc, false,
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InstDep.getInst(), &BB);
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}
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}
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}
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@ -54,3 +54,17 @@ define void @test5(i32* %Q) {
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; CHECK-NEXT: volatile load
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; CHECK-NEXT: ret void
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}
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declare void @llvm.memset.i32(i8*, i8, i32, i32)
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; Should delete store of 10 even though memset is a may-store to P (P and Q may
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; alias).
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define void @test6(i32 *%p, i8 *%q) {
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store i32 10, i32* %p, align 4 ;; dead.
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call void @llvm.memset.i32(i8* %q, i8 42, i32 900, i32 1)
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store i32 30, i32* %p, align 4
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ret void
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; CHECK: @test6
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; CHECK-NEXT: call void @llvm.memset
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}
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