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From: "ebotcazou at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/59461] New: missed zero-extension elimination in the combiner
Date: Tue, 10 Dec 2013 23:13:00 -0000	[thread overview]
Message-ID: <bug-59461-4@http.gcc.gnu.org/bugzilla/> (raw)

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.


             reply	other threads:[~2013-12-10 23:13 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-12-10 23:13 ebotcazou at gcc dot gnu.org [this message]
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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