https://bugs.llvm.org/show_bug.cgi?id=36076
Bug ID: 36076
Summary: Stores to union incorrectly reordered
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Created attachment 19739
--> https://bugs.llvm.org/attachment.cgi?id=19739&action=edit
minimal testcase
The attached test program is mis-compiled at all optimisation levels, except
-O0, for X86_64, Arm and likely for all targets.
./bin/clang -target x86_64-linux -O2 union-store.c
$ ./a.out
value = 3, should be 2
This happens in Dead Store Elimination:
*** IR Dump After Value Propagation ***
; Function Attrs: norecurse nounwind
define void @f() local_unnamed_addr #0 {
entry:
store i32 5, i32* getelementptr inbounds (%union.U, %union.U* @a, i32 0, i32
0), align 4, !tbaa !3
%0 = load i16*, i16** bitcast (%union.U** @b to i16**), align 4, !tbaa !6
store i16 3, i16* %0, align 4, !tbaa !3
store i16 2, i16* bitcast (%union.U* @a to i16*), align 4, !tbaa !3
ret void
}
*** IR Dump After Dead Store Elimination ***
; Function Attrs: norecurse nounwind
define void @f() local_unnamed_addr #0 {
entry:
store i32 2, i32* getelementptr inbounds (%union.U, %union.U* @a, i32 0, i32
0), align 4, !tbaa !3
%0 = load i16*, i16** bitcast (%union.U** @b to i16**), align 4, !tbaa !6
store i16 3, i16* %0, align 4, !tbaa !3
ret void
}
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