[Bug target/107172] [13 Regression] wrong code with "-O1 -ftree-vrp" on x86_64-linux-gnu since r13-1268-g8c99e307b20c502e
cvs-commit at gcc dot gnu.org
gcc-bugzilla@gcc.gnu.org
Thu Oct 27 18:42:48 GMT 2022
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107172
--- Comment #46 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by H.J. Lu <hjl@gcc.gnu.org>:
https://gcc.gnu.org/g:0e36a9c6915c713d30016cbade97a4b31dcc1350
commit r13-3530-g0e36a9c6915c713d30016cbade97a4b31dcc1350
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Thu Oct 20 11:55:19 2022 -0700
x86: Replace ne:CCC/ne:CCO with UNSPEC_CC_NE in neg patterns
In i386.md, neg patterns which set MODE_CC register like
(set (reg:CCC FLAGS_REG)
(ne:CCC (match_operand:SWI48 1 "general_reg_operand") (const_int 0)))
can lead to errors when operand 1 is a constant value. If FLAGS_REG in
(set (reg:CCC FLAGS_REG)
(ne:CCC (const_int 2) (const_int 0)))
is set to 1, RTX simplifiers may simplify
(set (reg:SI 93)
(neg:SI (ltu:SI (reg:CCC 17 flags) (const_int 0 [0]))))
as
(set (reg:SI 93)
(neg:SI (ltu:SI (const_int 1) (const_int 0 [0]))))
which leads to incorrect results since LTU on MODE_CC register isn't the
same as "unsigned less than" in x86 backend. To prevent RTL optimizers
from setting MODE_CC register to a constant, use UNSPEC_CC_NE to replace
ne:CCC/ne:CCO when setting FLAGS_REG in neg patterns.
gcc/
PR target/107172
* config/i386/i386.md (UNSPEC_CC_NE): New.
Replace ne:CCC/ne:CCO with UNSPEC_CC_NE in neg patterns.
gcc/testsuite/
PR target/107172
* gcc.target/i386/pr107172.c: New test.
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