diff options
author | Hans Wennborg <hans@hanshq.net> | 2018-08-13 08:28:30 +0000 |
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committer | Hans Wennborg <hans@hanshq.net> | 2018-08-13 08:28:30 +0000 |
commit | 18c17c4874875bbcfe587a0a65a6bb77e91bb92d (patch) | |
tree | 2a520309866eff032e7dc7f39e8bd4ad7989e6fd | |
parent | b4d5f64917bf8edf52bcc52434b0752e1ca12994 (diff) |
Merging r339411:
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r339411 | gbiv | 2018-08-10 07:14:43 +0200 (Fri, 10 Aug 2018) | 17 lines
[MemorySSA] "Fix" lifetime intrinsic handling
MemorySSA currently creates MemoryAccesses for lifetime intrinsics, and
sometimes treats them as clobbers. This may/may not be the best way
forward, but while we're doing it, we should consider
MayAlias/PartialAlias to be clobbers.
The ideal fix here is probably to remove all of this reasoning about
lifetimes from MemorySSA + put it into the passes that need to care. But
that's a wayyy broader fix that needs some consensus, and we have
miscompiles + a release branch today, and this should solve the
miscompiles just as well.
differential revision is D43269. Landing without an explicit LGTM (and
without using the special please-autoclose-this syntax) so we can still
use that revision as a place to decide what the right fix here is.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_70@339545 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r-- | lib/Analysis/MemorySSA.cpp | 9 | ||||
-rw-r--r-- | test/Transforms/EarlyCSE/memoryssa.ll | 42 | ||||
-rw-r--r-- | unittests/Analysis/MemorySSA.cpp | 66 |
3 files changed, 115 insertions, 2 deletions
diff --git a/lib/Analysis/MemorySSA.cpp b/lib/Analysis/MemorySSA.cpp index f57d490ce96..b38c0c4f143 100644 --- a/lib/Analysis/MemorySSA.cpp +++ b/lib/Analysis/MemorySSA.cpp @@ -258,13 +258,18 @@ static ClobberAlias instructionClobbersQuery(MemoryDef *MD, if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(DefInst)) { // These intrinsics will show up as affecting memory, but they are just - // markers. + // markers, mostly. + // + // FIXME: We probably don't actually want MemorySSA to model these at all + // (including creating MemoryAccesses for them): we just end up inventing + // clobbers where they don't really exist at all. Please see D43269 for + // context. switch (II->getIntrinsicID()) { case Intrinsic::lifetime_start: if (UseCS) return {false, NoAlias}; AR = AA.alias(MemoryLocation(II->getArgOperand(1)), UseLoc); - return {AR == MustAlias, AR}; + return {AR != NoAlias, AR}; case Intrinsic::lifetime_end: case Intrinsic::invariant_start: case Intrinsic::invariant_end: diff --git a/test/Transforms/EarlyCSE/memoryssa.ll b/test/Transforms/EarlyCSE/memoryssa.ll index 1c10efe2293..41e8d488ab4 100644 --- a/test/Transforms/EarlyCSE/memoryssa.ll +++ b/test/Transforms/EarlyCSE/memoryssa.ll @@ -106,3 +106,45 @@ end: store i32 %v2, i32* @G3 ret void } + +;; Check that we respect lifetime.start/lifetime.end intrinsics when deleting +;; stores that, without the lifetime calls, would be writebacks. +; CHECK-LABEL: @test_writeback_lifetimes( +; CHECK-NOMEMSSA-LABEL: @test_writeback_lifetimes( +define void @test_writeback_lifetimes(i32* %p) { +entry: + %q = getelementptr i32, i32* %p, i64 1 + %pv = load i32, i32* %p + %qv = load i32, i32* %q + call void @llvm.lifetime.end.p0i8(i64 8, i32* %p) + call void @llvm.lifetime.start.p0i8(i64 8, i32* %p) + ; CHECK: store i32 %pv + ; CHECK-NOMEMSSA-LABEL: store i32 %pv + store i32 %pv, i32* %p + ; CHECK: store i32 %qv, i32* %q + ; CHECK-NOMEMSSA-LABEL: store i32 %qv, i32* %q + store i32 %qv, i32* %q + ret void +} + +;; Check that we respect lifetime.start/lifetime.end intrinsics when deleting +;; stores that, without the lifetime calls, would be writebacks. +; CHECK-LABEL: @test_writeback_lifetimes_multi_arg( +; CHECK-NOMEMSSA-LABEL: @test_writeback_lifetimes_multi_arg( +define void @test_writeback_lifetimes_multi_arg(i32* %p, i32* %q) { +entry: + %pv = load i32, i32* %p + %qv = load i32, i32* %q + call void @llvm.lifetime.end.p0i8(i64 8, i32* %p) + call void @llvm.lifetime.start.p0i8(i64 8, i32* %p) + ; CHECK: store i32 %pv + ; CHECK-NOMEMSSA-LABEL: store i32 %pv + store i32 %pv, i32* %p + ; CHECK: store i32 %qv, i32* %q + ; CHECK-NOMEMSSA-LABEL: store i32 %qv, i32* %q + store i32 %qv, i32* %q + ret void +} + +declare void @llvm.lifetime.end.p0i8(i64, i32*) +declare void @llvm.lifetime.start.p0i8(i64, i32*) diff --git a/unittests/Analysis/MemorySSA.cpp b/unittests/Analysis/MemorySSA.cpp index 1a1675faca1..0eb543b5477 100644 --- a/unittests/Analysis/MemorySSA.cpp +++ b/unittests/Analysis/MemorySSA.cpp @@ -1199,3 +1199,69 @@ TEST_F(MemorySSATest, TestStoreMayAlias) { ++I; } } + +TEST_F(MemorySSATest, LifetimeMarkersAreClobbers) { + // Example code: + // define void @a(i8* %foo) { + // %bar = getelementptr i8, i8* %foo, i64 1 + // store i8 0, i8* %foo + // store i8 0, i8* %bar + // call void @llvm.lifetime.end.p0i8(i64 8, i32* %p) + // call void @llvm.lifetime.start.p0i8(i64 8, i32* %p) + // store i8 0, i8* %foo + // store i8 0, i8* %bar + // ret void + // } + // + // Patterns like this are possible after inlining; the stores to %foo and %bar + // should both be clobbered by the lifetime.start call if they're dominated by + // it. + + IRBuilder<> B(C); + F = Function::Create( + FunctionType::get(B.getVoidTy(), {B.getInt8PtrTy()}, false), + GlobalValue::ExternalLinkage, "F", &M); + + // Make blocks + BasicBlock *Entry = BasicBlock::Create(C, "entry", F); + + B.SetInsertPoint(Entry); + Value *Foo = &*F->arg_begin(); + + Value *Bar = B.CreateGEP(Foo, B.getInt64(1), "bar"); + + B.CreateStore(B.getInt8(0), Foo); + B.CreateStore(B.getInt8(0), Bar); + + auto GetLifetimeIntrinsic = [&](Intrinsic::ID ID) { + return Intrinsic::getDeclaration(&M, ID, {Foo->getType()}); + }; + + B.CreateCall(GetLifetimeIntrinsic(Intrinsic::lifetime_end), + {B.getInt64(2), Foo}); + Instruction *LifetimeStart = B.CreateCall( + GetLifetimeIntrinsic(Intrinsic::lifetime_start), {B.getInt64(2), Foo}); + + Instruction *FooStore = B.CreateStore(B.getInt8(0), Foo); + Instruction *BarStore = B.CreateStore(B.getInt8(0), Bar); + + setupAnalyses(); + MemorySSA &MSSA = *Analyses->MSSA; + + MemoryAccess *LifetimeStartAccess = MSSA.getMemoryAccess(LifetimeStart); + ASSERT_NE(LifetimeStartAccess, nullptr); + + MemoryAccess *FooAccess = MSSA.getMemoryAccess(FooStore); + ASSERT_NE(FooAccess, nullptr); + + MemoryAccess *BarAccess = MSSA.getMemoryAccess(BarStore); + ASSERT_NE(BarAccess, nullptr); + + MemoryAccess *FooClobber = + MSSA.getWalker()->getClobberingMemoryAccess(FooAccess); + EXPECT_EQ(FooClobber, LifetimeStartAccess); + + MemoryAccess *BarClobber = + MSSA.getWalker()->getClobberingMemoryAccess(BarAccess); + EXPECT_EQ(BarClobber, LifetimeStartAccess); +} |