http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60086
--- Comment #8 from Marcin Krotkiewski <marcin.krotkiewski at gmail dot com> ---
(In reply to Andrey Belevantsev from comment #5)
> At this point insn 461 is dead but we do not notice, and it doesn't look
> easy. I think there was some suggestion in the original research for
> killing dead insn copies left after renaming but I don't remember offhand.
Following Alexanders suggestion, I compiled the test code with -mavx -O3
-fselective-scheduling2 -frename-registers. This seems to get rid of the dead
instructions and yields the desired scheduling:
.L5:
vmovapd (%rbx,%rdi), %ymm0
addq $1, %rsi
vmovapd (%r12,%rdi), %ymm3
vaddpd 0(%r13,%rdi), %ymm0, %ymm2
vaddpd (%r14,%rdi), %ymm3, %ymm4
vmovapd %ymm2, (%rbx,%rdi)
vmovapd %ymm4, (%r12,%rdi)
addq $32, %rdi
cmpq %rsi, %rdx
ja .L5
Alexander, I should maybe clarify that the 'good' code was prepared by hand,
modifying the 'bad' asm I got from gcc 4.7. Asm generated by gcc 4.4 was the
same. If that is what you were refering to.
I am a bit confused now. It seems that all fine and the desired asm can be
generated, so there is no real bug. But why is the original code compiled with
-O3 -mavx bad then? Is -fschedule-insns not enabled at -O2?
