http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56309
--- Comment #20 from Steven Bosscher <steven at gcc dot gnu.org> 2013-02-14 22:17:23 UTC --- (In reply to comment #12) > --- by-val-O3.s.orig 2013-02-14 18:06:56.000000000 +0100 > +++ by-val-O3.s 2013-02-14 18:07:23.000000000 +0100 > @@ -357,9 +357,8 @@ > shrq $32, %rdi > cmpq %r8, %rdx > cmovbe %r11, %rdi > - addq $1, %rax > - cmpq %r8, %rdx > cmovbe %rdx, %rcx > + addq $1, %rax > cmpq %rbp, %rax > movq %rcx, -8(%rsi,%rax,8) > jne .L50 > > unmodified: Took 14.31 seconds total. > modified: Took 13.04 seconds total. > > So re. comment #9: it's not the problem but it'd be a small improvement. FWIW this comes from not eliminating the condition expression in the conditional moves that ifcvt creates: tmp_97 = tmp_93 > 4294967295 ? tmp_95 : tmp_93; carry_105 = tmp_93 > 4294967295 ? carry_94 : 0; I'm surprised this form is allowed at all, I'd expect we only allow is_gimple_reg() for a COND_EXPR_COND in a RHS context. Anyway -- separate problem.
