https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97603
Bug ID: 97603
Summary: Failure to optimize out compare into reuse of
subtraction result
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: gabravier at gmail dot com
Target Milestone: ---
int g();
int f(int a, int b)
{
if (a != b)
return a - b;
return g();
}
This can be optimized to using the result of `a - b` to check for `a != b`.
This is done by LLVM, but not by GCC. For example, on x86, LLVM generates this
:
f(int, int):
sub edi, esi
jne .LBB0_1
jmp g()
.LBB0_1:
mov eax, edi
ret
GCC generates this :
f(int, int):
cmp edi, esi
je .L7
mov eax, edi
sub eax, esi
ret
.L7:
jmp g()
