On 05/04/16 23:35, Segher Boessenkool wrote:
On Tue, Apr 05, 2016 at 10:48:58AM +0100, Kyrill Tkachov wrote:
So for the test gcc.dg/pr10474.c on arm with -marm -O3 before this patch we
perform shrink-wrapping:
cmp r0, #0
bxeq lr
push {r4, lr}
mov r4, r0
...
And after the patch we don't:
push {r4, lr}
subs r4, r0, #0
popeq {r4, pc}
...
The assembly after the "..." is identical.
So the resulting code is indeed shorter, though there is an
extra stack push and pop on the early return path.
A similar effect appears on gcc.dg/ira-shrinkwrap-prep-2.c.
The "new" code is better if there is no shrink-wrapping. We can probably
teach prepare_shrink_wrap to do the extra register move if that will allow
us to wrap more.
Though if so, it looks like a shrink-wrapping deficiency exposed by
this patch, rather than caused by it.
Yes, and mostly a testcase problem even.
Jakub, do you happen to have the before and after codegen for these tests
on ppc64? I wonder if the effect is more clearcut there.
RTL before shrink-wrapping would be useful, too.
So what shall we do for these tests for GCC 6?
Add an XFAIL for arm and powerpc?
Kyrill
Segher
