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[IRGen] Mark pointers as noalias when passing trivial types by value. #131885

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[IRGen] Mark pointers as noalias when passing trivial types by value. #131885

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7 changes: 4 additions & 3 deletions clang/lib/CodeGen/CGCall.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2797,9 +2797,10 @@ void CodeGenModule::ConstructAttributeList(StringRef Name,
Attrs.addByValAttr(getTypes().ConvertTypeForMem(ParamType));

auto *Decl = ParamType->getAsRecordDecl();
if (CodeGenOpts.PassByValueIsNoAlias && Decl &&
Decl->getArgPassingRestrictions() ==
RecordArgPassingKind::CanPassInRegs)
if (Decl && ((CodeGenOpts.PassByValueIsNoAlias &&
Decl->getArgPassingRestrictions() ==
RecordArgPassingKind::CanPassInRegs) ||
(!AI.getIndirectByVal() && Context.getTypeDeclType(Decl).isTrivialType(Context))))
// When calling the function, the pointer passed in will be the only
// reference to the underlying object. Mark it accordingly.
Attrs.addAttribute(llvm::Attribute::NoAlias);
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8 changes: 4 additions & 4 deletions clang/test/CodeGen/AArch64/byval-temp.c
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Expand Up @@ -30,10 +30,10 @@ void example(void) {
// Then, memcpy `l` to the temporary stack space.
// CHECK-O0-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 %[[byvaltemp]], ptr align 8 %[[l]], i64 64, i1 false)
// Finally, call using a pointer to the temporary stack space.
// CHECK-O0-NEXT: call void @pass_large(ptr noundef %[[byvaltemp]])
// CHECK-O0-NEXT: call void @pass_large(ptr noalias noundef %[[byvaltemp]])
// Now, do the same for the second call, using the second temporary alloca.
// CHECK-O0-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 %[[byvaltemp1]], ptr align 8 %[[l]], i64 64, i1 false)
// CHECK-O0-NEXT: call void @pass_large(ptr noundef %[[byvaltemp1]])
// CHECK-O0-NEXT: call void @pass_large(ptr noalias noundef %[[byvaltemp1]])
// CHECK-O0-NEXT: ret void
//
// At O3, we should have lifetime markers to help the optimizer re-use the temporary allocas.
Expand All @@ -58,15 +58,15 @@ void example(void) {
// Then, memcpy `l` to the temporary stack space.
// CHECK-O3-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 %[[byvaltemp]], ptr align 8 %[[l]], i64 64, i1 false)
// Finally, call using a pointer to the temporary stack space.
// CHECK-O3-NEXT: call void @pass_large(ptr noundef %[[byvaltemp]])
// CHECK-O3-NEXT: call void @pass_large(ptr noalias noundef %[[byvaltemp]])
//
// The lifetime of the temporary used to pass a pointer to the struct ends here.
// CHECK-O3-NEXT: call void @llvm.lifetime.end.p0(i64 64, ptr %[[byvaltemp]])
//
// Now, do the same for the second call, using the second temporary alloca.
// CHECK-O3-NEXT: call void @llvm.lifetime.start.p0(i64 64, ptr %[[byvaltemp1]])
// CHECK-O3-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 %[[byvaltemp1]], ptr align 8 %[[l]], i64 64, i1 false)
// CHECK-O3-NEXT: call void @pass_large(ptr noundef %[[byvaltemp1]])
// CHECK-O3-NEXT: call void @pass_large(ptr noalias noundef %[[byvaltemp1]])
// CHECK-O3-NEXT: call void @llvm.lifetime.end.p0(i64 64, ptr %[[byvaltemp1]])
//
// Mark the end of the lifetime of `l`.
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2 changes: 1 addition & 1 deletion clang/test/CodeGen/atomic-arm64.c
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Expand Up @@ -57,7 +57,7 @@ void test3(pointer_pair_t pair) {
}

// CHECK-LABEL:define{{.*}} void @test4(
// CHECK-SAME: ptr noundef [[QUAD:%.*]])
// CHECK-SAME: ptr noalias noundef [[QUAD:%.*]])
// CHECK: [[QUAD_INDIRECT_ADDR:%.*]] = alloca ptr, align 8
// CHECK-NEXT: [[TEMP:%.*]] = alloca [[QUAD_T:%.*]], align 8
// CHECK-NEXT: store ptr [[QUAD]], ptr [[QUAD_INDIRECT_ADDR]]
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2 changes: 1 addition & 1 deletion clang/test/CodeGen/attr-noundef.cpp
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Expand Up @@ -35,7 +35,7 @@ struct Huge {
Huge ret_huge() { return {}; }
void pass_huge(Huge h) {}
// CHECK: [[DEF]] void @{{.*}}ret_huge{{.*}}(ptr dead_on_unwind noalias writable sret({{[^)]+}}) align 4 %
// CHECK: [[DEF]] void @{{.*}}pass_huge{{.*}}(ptr noundef
// CHECK: [[DEF]] void @{{.*}}pass_huge{{.*}}(ptr noalias noundef
} // namespace check_structs

//************ Passing unions by value
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