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[Bug target/54829] bad optimization: sub followed by cmp w/ zero (ARM)
- From: "hjl.tools at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Sat, 06 Oct 2012 13:31:00 +0000
- Subject: [Bug target/54829] bad optimization: sub followed by cmp w/ zero (ARM)
- Auto-submitted: auto-generated
- References: <bug-54829-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54829
H.J. Lu <hjl.tools at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|bad optimization: sub |bad optimization: sub
|followed by cmp w/ zero |followed by cmp w/ zero
|(x86 & ARM) |(ARM)
--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> 2012-10-06 13:31:00 UTC ---
i386.md has
(define_insn "*cmp<mode>_minus_1"
[(set (reg FLAGS_REG)
(compare
(minus:SWI (match_operand:SWI 0 "nonimmediate_operand" "<r>m,<r>")
(match_operand:SWI 1 "<general_operand>" "<r><i>,<r>m"))
(const_int 0)))]
"ix86_match_ccmode (insn, CCGOCmode)"
"cmp{<imodesuffix>}\t{%1, %0|%0, %1}"
[(set_attr "type" "icmp")
(set_attr "mode" "<MODE>")])
Since cmp will also set OF and CF flags, it can't be used for GT and LE
which checks OF.