http://llvm.org/bugs/show_bug.cgi?id=20376
Bug ID: 20376
Summary: may fail to recognize potential EFLAGS clobbers for
compare-exchange operations
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Given the following IR:
declare void @g()
declare void @h()
declare void @i()
define void @cx(i64* %foo, i64 %bar, i64 %baz) {
%cx = cmpxchg i64* %foo, i64 %bar, i64 %baz seq_cst seq_cst
%p = extractvalue { i64, i1 } %cx, 1
call void @g()
br i1 %p, label %t, label %f
t:
call void @h()
ret void
f:
call void @i()
ret void
}
we currently generate the following x86 code for the entry block of @cx:
cx: # @cx
.cfi_startproc
# BB#0:
pushq %rax
.Ltmp0:
.cfi_def_cfa_offset 16
movq %rsi, %rax
lock
cmpxchgq %rdx, (%rdi)
callq g
jne .LBB0_2
This is clearly wrong, as the external call may clobber EFLAGS.
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