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[Bug target/29793] TESTW{W,L,Q} rCX + JZ/JE should be replaced by J{,E,R}CXZ when possible
- From: "ubizjak at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 5 Apr 2007 11:29:31 -0000
- Subject: [Bug target/29793] TESTW{W,L,Q} rCX + JZ/JE should be replaced by J{,E,R}CXZ when possible
- References: <bug-29793-10309@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #4 from ubizjak at gmail dot com 2007-04-05 12:29 -------
(In reply to comment #2)
> To implement this optimization, some support from assembler is needed. When
> displacement overflows 8bit, assembler should substitute "jecxz" with
> equivalent "test/jmp rel{16,32}" sequence.
Unfortunatelly, test/jmp clobbers flags, and jecxz doesn't. Due to this, and
example in comment #3, we can't reliably generate proposed instructions.
--
ubizjak at gmail dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |WONTFIX
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29793