https://llvm.org/bugs/show_bug.cgi?id=31614
Hans Wennborg <h...@chromium.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
CC| |ahmed.bouga...@gmail.com
Resolution|--- |FIXED
--- Comment #2 from Hans Wennborg <h...@chromium.org> ---
(In reply to comment #1)
> Hans, this looks like PR31367
> (https://llvm.org/bugs/show_bug.cgi?id=31367#c8). What do you think?
Yes, that's exactly it. The bug was introduced in r265636, i.e. llvm 3.9.
My best idea for working around it would be doing the fetch_add operation in a
noinline function :-/
My fix in r291630, which will be in llvm 4, affects the repro like this:
@@ -19,12 +19,13 @@
_Z13test_functionv: # @_Z13test_functionv
.cfi_startproc
# BB#0: # %entry
+ movl $1, %eax
+ lock xaddq %rax, foo(%rip)
testq %rax, %rax
setns %al
- lock incq foo(%rip)
movl $value_a, %ecx
movl $value_b, %edx
- cmovgq %rcx, %rdx
+ cmovnsq %rcx, %rdx
cmpl $100, (%rdx)
je .LBB1_3
# BB#1:
@@ -37,11 +38,12 @@
movl $foo+16, %eax
cmovneq %rcx, %rax
lock incq (%rax)
+ movl $1, %eax
+ lock xaddq %rax, foo(%rip)
testq %rax, %rax
setns %al
- lock incq foo(%rip)
movl $value_b, %esi
- cmovgq %rdx, %rsi
+ cmovnsq %rdx, %rsi
cmpl $100, (%rsi)
jne .LBB1_2
.LBB1_3: # %if.end.thread
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