[Clang][OpenMP] Fix the issue that llvm.lifetime.end is emitted too early for variables captured in linear clause
Currently if an OpenMP program uses `linear` clause, and is compiled with
optimization, `llvm.lifetime.end` for variables listed in `linear` clause are
emitted too early such that there could still be uses after that. Let's take the
following code as example:
```
// loop.c
int j;
int *u;
void loop(int n) {
int i;
for (i = 0; i < n; ++i) {
++j;
u = &j;
}
}
```
We compile using the command:
```
clang -cc1 -fopenmp-simd -O3 -x c -triple x86_64-apple-darwin10 -emit-llvm loop.c -o loop.ll
```
The following IR (simplified) will be generated:
```
@j = local_unnamed_addr global i32 0, align 4
@u = local_unnamed_addr global ptr null, align 8
define void @loop(i32 noundef %n) local_unnamed_addr {
entry:
%j = alloca i32, align 4
%cmp = icmp sgt i32 %n, 0
br i1 %cmp, label %simd.if.then, label %simd.if.end
simd.if.then: ; preds = %entry
call void @llvm.lifetime.start.p0(i64 4, ptr nonnull %j)
store ptr %j, ptr @u, align 8
call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %j)
%0 = load i32, ptr %j, align 4
store i32 %0, ptr @j, align 4
br label %simd.if.end
simd.if.end: ; preds = %simd.if.then, %entry
ret void
}
```
The most important part is:
```
call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %j)
%0 = load i32, ptr %j, align 4
store i32 %0, ptr @j, align 4
```
`%j` is still loaded after `@llvm.lifetime.end.p0(i64 4, ptr nonnull %j)`. This
could cause the backend incorrectly optimizes the code and further generates
incorrect code. The root cause is, when we emit a construct that could have
`linear` clause, it usually has the following pattern:
```
EmitOMPLinearClauseInit(S)
{
OMPPrivateScope LoopScope(*this);
...
EmitOMPLinearClause(S, LoopScope);
...
(void)LoopScope.Privatize();
...
}
EmitOMPLinearClauseFinal(S, [](CodeGenFunction &) { return nullptr; });
```
Variables that need to be privatized are added into `LoopScope`, which also
serves as a RAII object. When `LoopScope` is destructed and if optimization is
enabled, a `@llvm.lifetime.end` is also emitted for each privatized variable.
However, the writing back to original variables in `linear` clause happens after
the scope in `EmitOMPLinearClauseFinal`, causing the issue we see above.
A quick "fix" seems to be, moving `EmitOMPLinearClauseFinal` inside the scope.
However, it doesn't work. That's because the local variable map has been updated
by `LoopScope` such that a variable declaration is mapped to the privatized
variable, instead of the actual one. In that way, the following code will be
generated:
```
%0 = load i32, ptr %j, align 4
store i32 %0, ptr %j, align 4
call void @llvm.lifetime.end.p0(i64 4, ptr nonnull %j)
```
Well, now the life time is correct, but apparently the writing back is broken.
In this patch, a new function `OMPPrivateScope::restoreMap` is added and called
before calling `EmitOMPLinearClauseFinal`. This can make sure that
`EmitOMPLinearClauseFinal` can find the orignal varaibls to write back.
Fixes #56913.
Reviewed By: ABataev
Differential Revision: https://reviews.llvm.org/D131272
(cherry picked from commit e21202dac18ed7f718d26a0e131f96b399b4891c)
This commit is contained in:
Shilei Tian
Tobias Hieta
parent
5932bf1730
commit
a9ac5ac728
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@ -2582,8 +2582,9 @@ static void emitOMPSimdRegion(CodeGenFunction &CGF, const OMPLoopDirective &S,
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CGF.EmitOMPReductionClauseFinal(S, /*ReductionKind=*/OMPD_simd);
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emitPostUpdateForReductionClause(CGF, S,
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[](CodeGenFunction &) { return nullptr; });
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LoopScope.restoreMap();
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CGF.EmitOMPLinearClauseFinal(S, [](CodeGenFunction &) { return nullptr; });
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}
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CGF.EmitOMPLinearClauseFinal(S, [](CodeGenFunction &) { return nullptr; });
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// Emit: if (PreCond) - end.
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if (ContBlock) {
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CGF.EmitBranch(ContBlock);
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@ -3426,11 +3427,12 @@ bool CodeGenFunction::EmitOMPWorksharingLoop(
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EmitOMPLastprivateClauseFinal(
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S, isOpenMPSimdDirective(S.getDirectiveKind()),
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Builder.CreateIsNotNull(EmitLoadOfScalar(IL, S.getBeginLoc())));
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LoopScope.restoreMap();
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EmitOMPLinearClauseFinal(S, [IL, &S](CodeGenFunction &CGF) {
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return CGF.Builder.CreateIsNotNull(
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CGF.EmitLoadOfScalar(IL, S.getBeginLoc()));
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});
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}
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EmitOMPLinearClauseFinal(S, [IL, &S](CodeGenFunction &CGF) {
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return CGF.Builder.CreateIsNotNull(
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CGF.EmitLoadOfScalar(IL, S.getBeginLoc()));
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});
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DoacrossCleanupScope.ForceCleanup();
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// We're now done with the loop, so jump to the continuation block.
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if (ContBlock) {
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@ -7658,6 +7660,7 @@ void CodeGenFunction::EmitOMPTaskLoopBasedDirective(const OMPLoopDirective &S) {
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CGF.GetAddrOfLocalVar(*LIP), /*Volatile=*/false,
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(*LIP)->getType(), S.getBeginLoc())));
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}
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LoopScope.restoreMap();
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CGF.EmitOMPLinearClauseFinal(S, [LIP, &S](CodeGenFunction &CGF) {
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return CGF.Builder.CreateIsNotNull(
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CGF.EmitLoadOfScalar(CGF.GetAddrOfLocalVar(*LIP), /*Volatile=*/false,
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@ -1094,7 +1094,7 @@ public:
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void ForceCleanup() {
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RunCleanupsScope::ForceCleanup();
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MappedVars.restore(CGF);
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restoreMap();
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}
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/// Exit scope - all the mapped variables are restored.
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@ -1108,6 +1108,11 @@ public:
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VD = VD->getCanonicalDecl();
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return !VD->isLocalVarDeclOrParm() && CGF.LocalDeclMap.count(VD) > 0;
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}
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/// Restore all mapped variables w/o clean up. This is usefully when we want
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/// to reference the original variables but don't want the clean up because
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/// that could emit lifetime end too early, causing backend issue #56913.
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void restoreMap() { MappedVars.restore(CGF); }
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};
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/// Save/restore original map of previously emitted local vars in case when we
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32
clang/test/OpenMP/bug56913.c
Normal file
32
clang/test/OpenMP/bug56913.c
Normal file
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@ -0,0 +1,32 @@
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// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --function-signature --include-generated-funcs --prefix-filecheck-ir-name _
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// RUN: %clang_cc1 -fopenmp-simd -O1 -x c -triple x86_64-apple-darwin10 -emit-llvm %s -o - | FileCheck %s --check-prefix=CHECK
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int j;
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int *u;
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void loop(int n) {
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int i;
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#pragma omp parallel master taskloop simd linear(j)
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for (i = 0; i < n; ++i) {
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++j;
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u = &j;
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}
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}
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// CHECK-LABEL: define {{[^@]+}}@loop
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// CHECK-SAME: (i32 noundef [[N:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
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// CHECK-NEXT: entry:
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// CHECK-NEXT: [[J:%.*]] = alloca i32, align 4
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// CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[N]], 0
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// CHECK-NEXT: br i1 [[CMP]], label [[SIMD_IF_THEN:%.*]], label [[SIMD_IF_END:%.*]]
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// CHECK: simd.if.then:
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// CHECK-NEXT: [[TMP0:%.*]] = load i32, ptr @j, align 4, !tbaa [[TBAA2:![0-9]+]]
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// CHECK-NEXT: call void @llvm.lifetime.start.p0(i64 4, ptr nonnull [[J]]) #[[ATTR2:[0-9]+]]
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// CHECK-NEXT: store ptr [[J]], ptr @u, align 8, !tbaa [[TBAA6:![0-9]+]], !llvm.access.group [[ACC_GRP8:![0-9]+]]
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// CHECK-NEXT: [[INC_LE:%.*]] = add i32 [[TMP0]], [[N]]
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// CHECK-NEXT: store i32 [[INC_LE]], ptr [[J]], align 4, !tbaa [[TBAA2]]
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// CHECK-NEXT: store i32 [[INC_LE]], ptr @j, align 4, !tbaa [[TBAA2]]
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// CHECK-NEXT: call void @llvm.lifetime.end.p0(i64 4, ptr nonnull [[J]]) #[[ATTR2]]
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// CHECK-NEXT: br label [[SIMD_IF_END]]
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// CHECK: simd.if.end:
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// CHECK-NEXT: ret void
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//
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@ -322,18 +322,18 @@ int main() {
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// CHECK1-NEXT: br label [[OMP_LOOP_EXIT:%.*]]
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// CHECK1: omp.loop.exit:
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// CHECK1-NEXT: call void @__kmpc_for_static_fini(%struct.ident_t* @[[GLOB2]], i32 [[TMP5]])
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// CHECK1-NEXT: [[TMP19:%.*]] = bitcast i64* [[DOTLVAR__ADDR]] to i8*
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// CHECK1-NEXT: call void @__kmpc_free(i32 [[TMP5]], i8* [[TMP19]], i8* inttoptr (i64 5 to i8*))
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// CHECK1-NEXT: [[TMP20:%.*]] = load i32, i32* [[DOTOMP_IS_LAST]], align 4
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// CHECK1-NEXT: [[TMP21:%.*]] = icmp ne i32 [[TMP20]], 0
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// CHECK1-NEXT: br i1 [[TMP21]], label [[DOTOMP_LINEAR_PU:%.*]], label [[DOTOMP_LINEAR_PU_DONE:%.*]]
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// CHECK1-NEXT: [[TMP19:%.*]] = load i32, i32* [[DOTOMP_IS_LAST]], align 4
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// CHECK1-NEXT: [[TMP20:%.*]] = icmp ne i32 [[TMP19]], 0
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// CHECK1-NEXT: br i1 [[TMP20]], label [[DOTOMP_LINEAR_PU:%.*]], label [[DOTOMP_LINEAR_PU_DONE:%.*]]
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// CHECK1: .omp.linear.pu:
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// CHECK1-NEXT: [[TMP22:%.*]] = load float*, float** [[PVAR2]], align 8
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// CHECK1-NEXT: store float* [[TMP22]], float** [[TMP0]], align 8
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// CHECK1-NEXT: [[TMP23:%.*]] = load i64, i64* [[DOTLVAR__ADDR]], align 8
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// CHECK1-NEXT: store i64 [[TMP23]], i64* [[TMP1]], align 8
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// CHECK1-NEXT: [[TMP21:%.*]] = load float*, float** [[PVAR2]], align 8
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// CHECK1-NEXT: store float* [[TMP21]], float** [[TMP0]], align 8
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// CHECK1-NEXT: [[TMP22:%.*]] = load i64, i64* [[DOTLVAR__ADDR]], align 8
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// CHECK1-NEXT: store i64 [[TMP22]], i64* [[TMP1]], align 8
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// CHECK1-NEXT: br label [[DOTOMP_LINEAR_PU_DONE]]
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// CHECK1: .omp.linear.pu.done:
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// CHECK1-NEXT: [[TMP23:%.*]] = bitcast i64* [[DOTLVAR__ADDR]] to i8*
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// CHECK1-NEXT: call void @__kmpc_free(i32 [[TMP5]], i8* [[TMP23]], i8* inttoptr (i64 5 to i8*))
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// CHECK1-NEXT: call void @__kmpc_barrier(%struct.ident_t* @[[GLOB1]], i32 [[TMP5]])
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// CHECK1-NEXT: ret void
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//
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@ -1847,8 +1847,12 @@ void loop() {
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// CHECK6-NEXT: [[TMP38:%.*]] = icmp ne i32 [[TMP37]], 0
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// CHECK6-NEXT: br i1 [[TMP38]], label [[DOTOMP_LINEAR_PU_I:%.*]], label [[DOTOMP_OUTLINED__1_EXIT:%.*]]
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// CHECK6: .omp.linear.pu.i:
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// CHECK6-NEXT: [[TMP39:%.*]] = load i32, i32* [[J_I]], align 4, !noalias !14
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// CHECK6-NEXT: store i32 [[TMP39]], i32* [[J_I]], align 4, !noalias !14
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// CHECK6-NEXT: [[TMP39:%.*]] = getelementptr inbounds [[STRUCT_ANON]], %struct.anon* [[TMP20]], i32 0, i32 0
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// CHECK6-NEXT: [[TMP40:%.*]] = load i32*, i32** [[TMP39]], align 8
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// CHECK6-NEXT: [[TMP41:%.*]] = getelementptr inbounds [[STRUCT_ANON]], %struct.anon* [[TMP20]], i32 0, i32 1
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// CHECK6-NEXT: [[TMP42:%.*]] = load i32*, i32** [[TMP41]], align 8
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// CHECK6-NEXT: [[TMP43:%.*]] = load i32, i32* [[J_I]], align 4, !noalias !14
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// CHECK6-NEXT: store i32 [[TMP43]], i32* [[TMP42]], align 4
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// CHECK6-NEXT: br label [[DOTOMP_OUTLINED__1_EXIT]]
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// CHECK6: .omp_outlined..1.exit:
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// CHECK6-NEXT: ret i32 0
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