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Merged
merged 2 commits into from
Aug 5, 2025
+30 −127
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[MemoryLocation] Compute lifetime size from alloca size #151982

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721c465
[MemoryLocation] Compute lifetime size from alloca size
nikic Aug 4, 2025
1fe88a4
remove size arg in test
nikic Aug 5, 2025
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16 changes: 15 additions & 1 deletion llvm/lib/Analysis/MemoryLocation.cpp
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Expand Up @@ -190,7 +190,21 @@ MemoryLocation MemoryLocation::getForArgument(const CallBase *Call,
return MemoryLocation::getAfter(Arg, AATags);

case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
case Intrinsic::lifetime_end: {
assert(ArgIdx == 1 && "Invalid argument index");
auto *AI = dyn_cast<AllocaInst>(Arg);
if (!AI)
// lifetime of poison value.
return MemoryLocation::getBeforeOrAfter(Arg);
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might be worth asserting here or does the verifier check?

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The verifier checks it (see #151148).

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Sounds good


std::optional<TypeSize> AllocSize =
AI->getAllocationSize(II->getDataLayout());
return MemoryLocation(Arg,
AllocSize ? LocationSize::precise(*AllocSize)
: LocationSize::afterPointer(),
AATags);
}

case Intrinsic::invariant_start:
assert(ArgIdx == 1 && "Invalid argument index");
return MemoryLocation(
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106 changes: 0 additions & 106 deletions llvm/test/Transforms/DeadStoreElimination/lifetime.ll
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Expand Up @@ -37,110 +37,4 @@ define void @test2(ptr %P) {
ret void
}

; lifetime.end only marks the first two bytes of %A as dead. Make sure
; `store i8 20, ptr %A.2 is not removed.
define void @test3_lifetime_end_partial() {
; CHECK-LABEL: @test3_lifetime_end_partial(
; CHECK-NEXT: [[A:%.*]] = alloca i32, align 4
; CHECK-NEXT: call void @llvm.lifetime.start.p0(i64 2, ptr [[A]])
; CHECK-NEXT: [[A_1:%.*]] = getelementptr i8, ptr [[A]], i64 1
; CHECK-NEXT: [[A_2:%.*]] = getelementptr i8, ptr [[A]], i64 2
; CHECK-NEXT: store i8 20, ptr [[A_2]], align 1
; CHECK-NEXT: call void @llvm.lifetime.end.p0(i64 2, ptr [[A]])
; CHECK-NEXT: call void @use(ptr [[A_1]])
; CHECK-NEXT: ret void
;
%A = alloca i32

call void @llvm.lifetime.start.p0(i64 2, ptr %A)
%A.1 = getelementptr i8, ptr %A, i64 1
%A.2 = getelementptr i8, ptr %A, i64 2

store i8 0, ptr %A
store i8 10, ptr %A.1
store i8 20, ptr %A.2

call void @llvm.lifetime.end.p0(i64 2, ptr %A)
call void @use(ptr %A.1)
ret void
}

; lifetime.end only marks the first two bytes of %A as dead. Make sure
; `store i8 20, ptr %A.2 is not removed.
define void @test4_lifetime_end_partial_loop() {
; CHECK-LABEL: @test4_lifetime_end_partial_loop(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[A:%.*]] = alloca i32, align 4
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i8 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[LOOP]] ]
; CHECK-NEXT: call void @llvm.lifetime.start.p0(i64 2, ptr [[A]])
; CHECK-NEXT: [[A_1:%.*]] = getelementptr i8, ptr [[A]], i64 1
; CHECK-NEXT: [[A_2:%.*]] = getelementptr i8, ptr [[A]], i64 2
; CHECK-NEXT: call void @use(ptr [[A_1]])
; CHECK-NEXT: store i8 20, ptr [[A_2]], align 1
; CHECK-NEXT: call void @llvm.lifetime.end.p0(i64 2, ptr [[A]])
; CHECK-NEXT: [[IV_NEXT]] = add i8 [[IV]], 10
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp eq i8 [[IV_NEXT]], 10
; CHECK-NEXT: br i1 [[EXITCOND]], label [[EXIT:%.*]], label [[LOOP]]
; CHECK: exit:
; CHECK-NEXT: ret void
;
entry:
%A = alloca i32

br label %loop

loop:
%iv = phi i8 [ 0, %entry ], [ %iv.next, %loop ]
call void @llvm.lifetime.start.p0(i64 2, ptr %A)
%A.1 = getelementptr i8, ptr %A, i64 1
%A.2 = getelementptr i8, ptr %A, i64 2

call void @use(ptr %A.1)

store i8 20, ptr %A.2
store i8 10, ptr %A.1
store i8 0, ptr %A
call void @llvm.lifetime.end.p0(i64 2, ptr %A)

%iv.next = add i8 %iv, 10
%exitcond = icmp eq i8 %iv.next, 10
br i1 %exitcond, label %exit, label %loop

exit:
ret void
}

; lifetime.end only marks the first two bytes of %A as dead. Make sure
; `store i8 20, ptr %A.2 is not removed.
define void @test5_lifetime_end_partial() {
; CHECK-LABEL: @test5_lifetime_end_partial(
; CHECK-NEXT: [[A:%.*]] = alloca [4 x i8], align 1
; CHECK-NEXT: call void @llvm.lifetime.start.p0(i64 2, ptr [[A]])
; CHECK-NEXT: [[A_1:%.*]] = getelementptr i8, ptr [[A]], i64 1
; CHECK-NEXT: [[A_2:%.*]] = getelementptr i8, ptr [[A]], i64 2
; CHECK-NEXT: store i8 20, ptr [[A_2]], align 1
; CHECK-NEXT: call void @llvm.lifetime.end.p0(i64 2, ptr [[A]])
; CHECK-NEXT: call void @use(ptr [[A_1]])
; CHECK-NEXT: ret void
;

%A = alloca [4 x i8]
call void @llvm.lifetime.start.p0(i64 2, ptr %A)
%A.1 = getelementptr i8, ptr %A, i64 1
%A.2 = getelementptr i8, ptr %A, i64 2

store i8 0, ptr %A
store i8 10, ptr %A.1
store i8 20, ptr %A.2

call void @llvm.lifetime.end.p0(i64 2, ptr %A)

call void @use(ptr %A.1)
store i8 30, ptr %A.1
store i8 40, ptr %A.2
ret void
}

declare void @use(ptr) readonly
35 changes: 15 additions & 20 deletions llvm/unittests/Analysis/MemorySSATest.cpp
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Expand Up @@ -1086,16 +1086,17 @@ TEST_F(MemorySSATest, TestStoreMayAlias) {

TEST_F(MemorySSATest, LifetimeMarkersAreClobbers) {
// Example code:
// define void @a(i8* %foo) {
// %bar = getelementptr i8, i8* %foo, i64 1
// %baz = getelementptr i8, i8* %foo, i64 2
// store i8 0, i8* %foo
// store i8 0, i8* %bar
// call void @llvm.lifetime.end.p0i8(i64 3, i8* %foo)
// call void @llvm.lifetime.start.p0i8(i64 3, i8* %foo)
// store i8 0, i8* %foo
// store i8 0, i8* %bar
// call void @llvm.memset.p0i8(i8* %baz, i8 0, i64 1)
// define void @a() {
// %foo = alloca i32
// %bar = getelementptr i8, ptr %foo, i64 1
// %baz = getelementptr i8, ptr %foo, i64 2
// store i8 0, ptr %foo
// store i8 0, ptr %bar
// call void @llvm.lifetime.end.p0(i64 3, ptr %foo)
// call void @llvm.lifetime.start.p0(i64 3, ptr %foo)
// store i8 0, ptr %foo
// store i8 0, ptr %bar
// call void @llvm.memset.p0i8(ptr %baz, i8 0, i64 1)
// ret void
// }
//
Expand All @@ -1104,29 +1105,23 @@ TEST_F(MemorySSATest, LifetimeMarkersAreClobbers) {
// it.

IRBuilder<> B(C);
F = Function::Create(FunctionType::get(B.getVoidTy(), {B.getPtrTy()}, false),
F = Function::Create(FunctionType::get(B.getVoidTy(), {}, false),
GlobalValue::ExternalLinkage, "F", &M);

// Make blocks
BasicBlock *Entry = BasicBlock::Create(C, "entry", F);

B.SetInsertPoint(Entry);
Value *Foo = &*F->arg_begin();
Value *Foo = B.CreateAlloca(B.getInt32Ty());

Value *Bar = B.CreatePtrAdd(Foo, B.getInt64(1), "bar");
Value *Baz = B.CreatePtrAdd(Foo, B.getInt64(2), "baz");

B.CreateStore(B.getInt8(0), Foo);
B.CreateStore(B.getInt8(0), Bar);

auto GetLifetimeIntrinsic = [&](Intrinsic::ID ID) {
return Intrinsic::getOrInsertDeclaration(&M, ID, {Foo->getType()});
};

B.CreateCall(GetLifetimeIntrinsic(Intrinsic::lifetime_end),
{B.getInt64(3), Foo});
Instruction *LifetimeStart = B.CreateCall(
GetLifetimeIntrinsic(Intrinsic::lifetime_start), {B.getInt64(3), Foo});
B.CreateLifetimeEnd(Foo);
Instruction *LifetimeStart = B.CreateLifetimeStart(Foo);

Instruction *FooStore = B.CreateStore(B.getInt8(0), Foo);
Instruction *BarStore = B.CreateStore(B.getInt8(0), Bar);
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