https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88676
Bug ID: 88676
Summary: missed opportunity is integer conditional
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: drepper.fsp+rhbz at gmail dot com
Target Milestone: ---
Take the following code:
int f(unsigned b)
{
int r;
if (b >= 2)
__builtin_unreachable();
switch (b) {
case 0:
r = 1;
break;
case 1:
r = 2;
break;
default:
r = 0;
break;
}
return r;
}
Compiled using the current trunk gcc and gcc 8.2.1 with -O3 on x86_64 the
following code is produced:
0000000000000000 <f>:
0: 31 c0 xor %eax,%eax
2: 83 ff 01 cmp $0x1,%edi
5: 0f 94 c0 sete %al
8: ff c0 inc %eax
a: c3 retq
This is quite good but it should be something like
leal 1(%edi),%eax
ret
The first three instructions test for 0 or 1 and load into %eax the values 0 or
1 respectively. This should be just a move.
