http://llvm.org/bugs/show_bug.cgi?id=8589
Summary: Wrong atomic intrinsic codegen at -O0
Product: new-bugs
Version: unspecified
Platform: PC
OS/Version: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Running "llc -O1" (or higher -O level) on the attached testcase results in
correct code. But with "llc -O0", an atomic operation is reordered wrongly:
call void @GOMP_loop_end_nowait() nounwind
%13 = getelementptr inbounds i8* %.omp_data_i, i64 8
%14 = bitcast i8* %13 to i32*
call void @llvm.memory.barrier(i1 true, i1 true, i1 true, i1 true, i1 true)
%15 = call i32 @llvm.atomic.load.and.i32.p0i32(i32* %14, i32 %12)
call void @llvm.memory.barrier(i1 true, i1 true, i1 true, i1 true, i1 true)
->
lock
cmpxchgl %ecx, (%rsi)
movl %eax, (%rsp) # 4-byte Spill
jne .LBB0_6
# BB#7: # %6
callq GOMP_loop_end_nowait
movabsq $8, %rax
movq 88(%rsp), %rcx # 8-byte Reload
addq %rcx, %rax
mfence
mfence
There are several crazy things here. First off, the atomic operation has
been moved before the call to GOMP_loop_end_nowait, which is just wrong
since it writes to memory that is manipulated by GOMP_loop_end_nowait.
It has also been moved out from between the memory barriers (leaving the
two lonely "mfence" instructions with the atomic no longer between them!).
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