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* [Bug rtl-optimization/59461] New: missed zero-extension elimination in the combiner
@ 2013-12-10 23:13 ebotcazou at gcc dot gnu.org
2013-12-10 23:14 ` [Bug rtl-optimization/59461] " ebotcazou at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: ebotcazou at gcc dot gnu.org @ 2013-12-10 23:13 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59461
Bug ID: 59461
Summary: missed zero-extension elimination in the combiner
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: ebotcazou at gcc dot gnu.org
This is a spin-off of PR rtl-optimization/58295. The zero-extension is not
(and has never been) eliminated on the SPARC at -O2:
ee_isdigit2:
sethi %hi(zeb_test_array), %g1
or %g1, %lo(zeb_test_array), %g1
ldub [%g1+%o0], %g1
mov 0, %o0
add %g1, -48, %g1
and %g1, 0xff, %g1
cmp %g1, 9
jmp %o7+8
movleu %icc, 1, %o0
.size ee_isdigit2, .-ee_isdigit2
The instruction "and %g1, 0xff, %g1" is redundant like on the ARM and the
combiner should eliminate it. The difference between the ARM and the SPARC is
that the former explicitly zero-extends the load from memory while the latter
does it only implicitly via LOAD_EXTEND_OP. This shouldn't matter in the end,
but does here because of some weakness of the nonzero_bits machinery.
^ permalink raw reply [flat|nested] 4+ messages in thread* [Bug rtl-optimization/59461] missed zero-extension elimination in the combiner 2013-12-10 23:13 [Bug rtl-optimization/59461] New: missed zero-extension elimination in the combiner ebotcazou at gcc dot gnu.org @ 2013-12-10 23:14 ` ebotcazou at gcc dot gnu.org 2013-12-11 9:23 ` rguenth at gcc dot gnu.org 2013-12-11 9:51 ` ebotcazou at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: ebotcazou at gcc dot gnu.org @ 2013-12-10 23:14 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59461 Eric Botcazou <ebotcazou at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |ASSIGNED Last reconfirmed| |2013-12-10 Assignee|unassigned at gcc dot gnu.org |ebotcazou at gcc dot gnu.org Ever confirmed|0 |1 Severity|normal |enhancement --- Comment #1 from Eric Botcazou <ebotcazou at gcc dot gnu.org> --- I'll look into this at some point. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/59461] missed zero-extension elimination in the combiner 2013-12-10 23:13 [Bug rtl-optimization/59461] New: missed zero-extension elimination in the combiner ebotcazou at gcc dot gnu.org 2013-12-10 23:14 ` [Bug rtl-optimization/59461] " ebotcazou at gcc dot gnu.org @ 2013-12-11 9:23 ` rguenth at gcc dot gnu.org 2013-12-11 9:51 ` ebotcazou at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: rguenth at gcc dot gnu.org @ 2013-12-11 9:23 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59461 --- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> --- I wonder if x86_64 is also affected as it has implicitely zero/sign-extending loads as well. ^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/59461] missed zero-extension elimination in the combiner 2013-12-10 23:13 [Bug rtl-optimization/59461] New: missed zero-extension elimination in the combiner ebotcazou at gcc dot gnu.org 2013-12-10 23:14 ` [Bug rtl-optimization/59461] " ebotcazou at gcc dot gnu.org 2013-12-11 9:23 ` rguenth at gcc dot gnu.org @ 2013-12-11 9:51 ` ebotcazou at gcc dot gnu.org 2 siblings, 0 replies; 4+ messages in thread From: ebotcazou at gcc dot gnu.org @ 2013-12-11 9:51 UTC (permalink / raw) To: gcc-bugs http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59461 --- Comment #3 from Eric Botcazou <ebotcazou at gcc dot gnu.org> --- > I wonder if x86_64 is also affected as it has implicitely zero/sign-extending > loads as well. Not for this testcase at least, where the code is (and has always been) optimal: ee_isdigit2: .LFB0: .cfi_startproc movl %edi, %edi movzbl zeb_test_array(%rdi), %eax subl $48, %eax cmpb $9, %al setbe %al ret .cfi_endproc because the x86-64 can perform the addition in QImode directly. ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2013-12-11 9:51 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2013-12-10 23:13 [Bug rtl-optimization/59461] New: missed zero-extension elimination in the combiner ebotcazou at gcc dot gnu.org 2013-12-10 23:14 ` [Bug rtl-optimization/59461] " ebotcazou at gcc dot gnu.org 2013-12-11 9:23 ` rguenth at gcc dot gnu.org 2013-12-11 9:51 ` ebotcazou at gcc dot gnu.org
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