https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109866
--- Comment #1 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Andrew Pinski from comment #0)
> Take:
> ```
> int g(void); int h(void); int t(void);
> int f(int a, int b)
> {
> int c = a - b;
> if(c == 0)
> return g();
> if (c > 0)
> return h();
> return t();
> }
> ```
> This is reduced from bzip2 in spec 2006, though I am not so sure any more.
> On x86_64 GCC produces:
> ```
> subl %esi, %edi
> testl %edi, %edi
> je .L5
> jle .L3
> jmp h()
> .L3:
> jmp t()
> .L5:
> jmp g()
> ```
> But GCC should produce (likes clang/LLVM does):
> ```
> cmpl %esi, %edi
> je .L5
> jle .L3
> jmp h()
> .L3:
> jmp t()
> .L5:
> jmp g()
> ```
>
> Note a similar thing happens with aarch64 target too.
These two assemblies are not equal as demonstrated by the following test:
--cut here--
#include <stdio.h>
_Bool
__attribute__((noinline))
foo (int a, int b)
{
_Bool r;
int tmp;
asm ("subl %3, %0; testl %0, %0"
: "=r"(tmp), "=@cc" "le"(r)
: "0"(a), "r"(b));
return r;
}
_Bool
__attribute__((noinline))
bar (int a, int b)
{
_Bool r;
asm ("cmpl %2, %1"
: "=@cc" "le"(r)
: "r"(a), "r"(b));
return r;
}
int
main ()
{
int a, b;
_Bool ra, rb;
a = 0x80000000, b = 0x40000000;
ra = foo (a, b);
rb = bar (a, b);
printf ("%i %i\n", ra, rb);
return 0;
}
--cut here--
$ ./a.out
0 1
The difference is in handling of overflow flag.
