https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85756
Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Version|unknown |9.0
Last reconfirmed| |2018-05-12
Component|tree-optimization |target
CC| |ebotcazou at gcc dot gnu.org,
| |jakub at gcc dot gnu.org
Blocks| |85683
Ever confirmed|0 |1
Summary|wrong code at -Os on |[9 regression] wrong code
|x86-64-linux-gnu in 32-bit |at -Os on x86-64-linux-gnu
|mode |in 32-bit mode
Target Milestone|--- |9.0
Severity|normal |major
--- Comment #1 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
This was introduced by:
PR target/85683
* config/i386/i386.md: Add peepholes for mem {+,-,&,|,^}= x; mem != 0
after cmpelim optimization.
--- pr85756_0.s 2018-05-12 12:23:29.214331432 +0200
+++ pr85756.s 2018-05-12 12:23:38.950611436 +0200
@@ -37,10 +37,9 @@
testw %ax, %ax
movl %edx, f
setne %al
- subl -44(%ebp), %esi
- setne %cl
- movl %esi, -44(%ebp)
+ subl %esi, -44(%ebp)
movl %edx, %esi
+ setne %cl
orl %ecx, %eax
movzbl %al, %eax
xorl %eax, %esi
The transformation swaps the operands of the subtraction. It's also
responsible for the miscompilation of the Ada runtime (g-catiio.o) in 32-bit
mode.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85683
[Bug 85683] [8 Regression] GCC 8 stopped using RMW (Read Modify Write)
instructions on x86[_64]
