This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
[Bug target/82580] Optimize comparisons for __int128 on x86-64
- From: "ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 18 Oct 2017 12:16:13 +0000
- Subject: [Bug target/82580] Optimize comparisons for __int128 on x86-64
- Auto-submitted: auto-generated
- References: <bug-82580-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82580
--- Comment #7 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Jakub Jelinek from comment #6)
> i.e. for the flags we first clear %eax and then setX %al, but for f2
> cmpq %rdi, %rdx
> sbbq %rsi, %rcx
> setb %al
> movzbl %al, %eax
> Seems this is done in
> ;; Convert setcc + movzbl to xor + setcc if operands don't overlap.
> peephole2s, do we need a peephole for this as well, or some more general
> peephole2 or other means of optimizing this?
No, this would break carry flag propagation from cmp to sbb.