https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88593
--- Comment #9 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Jeffrey A. Law from comment #8)
> That's an indication you've likely done something wrong with your local
> properties HJ. LCM inherently also does LICM since LICM is just a special
> case of PRE.
The LCM algorithm isn't appropriate here since it may place a vxorps
inside the loop. Simple testcase show this:
$ cat badcase.c
extern float f;
extern double d;
extern int i;
void
foo (int n, int k)
{
for (int j = 0; j != n; j++)
if (j < k)
d = f;
}
It generates
...
loop:
if(j < k)
vxorps %xmm0, %xmm0, %xmm0
vcvtss2sd %xmm1, %xmm0, %xmm0
...
loopend
...
This is because LCM only works when there is a certain benifit. But for
conditional branch, LCM wouldn't move
vxorps %xmm0, %xmm0, %xmm0
out of loop. It's suboptimal.
