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StackLifetime: Remove asserts for multiple lifetime intrinsics. 

According to the langref, it is valid to have multiple consecutive
lifetime start or end intrinsics on the same object.

For llvm.lifetime.start:
"If ptr [...] is a stack object that is already alive, it simply
fills all bytes of the object with poison."

For llvm.lifetime.end:
"Calling llvm.lifetime.end on an already dead alloca is no-op."

However, we currently fail an assertion in such cases. I've observed
the assertion failure when the loop vectorization pass duplicates
the intrinsic.

We can conservatively handle these intrinsics by ignoring all but
the first one, which can be implemented by removing the assertions.

Differential Revision: https://reviews.llvm.org/D108337
This commit is contained in:
Peter Collingbourne 2021-08-18 15:03:03 -07:00
parent 5fdaaf7fd8
commit 6f85225ef3
2 changed files with 25 additions and 2 deletions
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2
llvm/lib/Analysis/StackLifetime.cpp
View File

@ -257,14 +257,12 @@ void StackLifetime::calculateLiveIntervals() {
unsigned AllocaNo = It.second.AllocaNo;
if (IsStart) {
assert(!Started.test(AllocaNo) || Start[AllocaNo] == BBStart);
if (!Started.test(AllocaNo)) {
Started.set(AllocaNo);
Ended.reset(AllocaNo);
Start[AllocaNo] = InstNo;
}
} else {
assert(!Ended.test(AllocaNo));
if (Started.test(AllocaNo)) {
LiveRanges[AllocaNo].addRange(Start[AllocaNo], InstNo);
Started.reset(AllocaNo);

25
llvm/test/Analysis/StackSafetyAnalysis/lifetime.ll
View File

@ -924,6 +924,31 @@ entry:
ret void
}
define void @multiple_start_end() {
; CHECK-LABEL: define void @multiple_start_end
entry:
; CHECK: entry:
; CHECK-NEXT: Alive: <>
%x = alloca i8
call void @llvm.lifetime.start.p0i8(i64 1, i8* %x)
; CHECK: call void @llvm.lifetime.start.p0i8(i64 1, i8* %x)
; CHECK-NEXT: Alive: <x>
call void @llvm.lifetime.start.p0i8(i64 1, i8* %x)
; CHECK: call void @llvm.lifetime.start.p0i8(i64 1, i8* %x)
; CHECK-NEXT: Alive: <x>
call void @llvm.lifetime.end.p0i8(i64 1, i8* %x)
; CHECK: call void @llvm.lifetime.end.p0i8(i64 1, i8* %x)
; CHECK-NEXT: Alive: <>
call void @llvm.lifetime.end.p0i8(i64 1, i8* %x)
; CHECK: call void @llvm.lifetime.end.p0i8(i64 1, i8* %x)
; CHECK-NEXT: Alive: <>
ret void
}
declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)
declare void @llvm.lifetime.start.p0i32(i64, i32* nocapture)