[Bug target/85683] [8 Regression] GCC 8 stopped using RMW (Read Modify Write) instructions on x86[_64]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85683 Jakub Jelinek changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |FIXED --- Comment #8 from Jakub Jelinek --- Fixed for 8.2+.
[Bug target/85683] [8 Regression] GCC 8 stopped using RMW (Read Modify Write) instructions on x86[_64]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85683
--- Comment #7 from Jakub Jelinek ---
Author: jakub
Date: Wed May 30 07:19:24 2018
New Revision: 260915
URL: https://gcc.gnu.org/viewcvs?rev=260915=gcc=rev
Log:
Backported from mainline
2018-05-08 Jakub Jelinek
PR target/85683
* config/i386/i386.md: Add peepholes for mem {+,-,&,|,^}= x; mem != 0
after cmpelim optimization.
* gcc.target/i386/pr49095.c: Add -masm=att to dg-options. Add
scan-assembler-times checking that except for [fh]*xor other functions
don't use any load instructions.
Modified:
branches/gcc-8-branch/gcc/ChangeLog
branches/gcc-8-branch/gcc/config/i386/i386.md
branches/gcc-8-branch/gcc/testsuite/ChangeLog
branches/gcc-8-branch/gcc/testsuite/gcc.target/i386/pr49095.c
[Bug target/85683] [8 Regression] GCC 8 stopped using RMW (Read Modify Write) instructions on x86[_64]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85683 Bug 85683 depends on bug 85756, which changed state. Bug 85756 Summary: [9 regression] wrong code at -Os on x86-64-linux-gnu in 32-bit mode https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85756 What|Removed |Added Status|NEW |RESOLVED Resolution|--- |FIXED
[Bug target/85683] [8 Regression] GCC 8 stopped using RMW (Read Modify Write) instructions on x86[_64]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85683 Jakub Jelinek changed: What|Removed |Added Summary|[8/9 Regression] GCC 8 |[8 Regression] GCC 8 |stopped using RMW (Read |stopped using RMW (Read |Modify Write) instructions |Modify Write) instructions |on x86[_64] |on x86[_64] --- Comment #6 from Jakub Jelinek --- Fixed for GCC9 so far, will backport to 8.2 after a while.
[Bug target/85683] [8 Regression] GCC 8 stopped using RMW (Read Modify Write) instructions on x86[_64]
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85683
Alexander Monakov changed:
What|Removed |Added
Keywords||missed-optimization
Status|UNCONFIRMED |NEW
Last reconfirmed||2018-05-07
CC||amonakov at gcc dot gnu.org
Ever confirmed|0 |1
--- Comment #1 from Alexander Monakov ---
Smaller testcase:
void f(void);
void g(int *p)
{
if (!--*p)
f();
}
On gcc-7.3 this is optimized by the peephole2 pass so it doesn't really help
with register pressure (combine pass seems more suitable for that); don't know
why the peephole doesn't trigger on gcc-8.
