https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85745
Bug ID: 85745
Summary: variable with asm register assignment allocated in
wrong reg
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: bernd.edlinger at hotmail dot de
Target Milestone: ---
Created attachment 44114
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44114&action=edit
reduced test case
This prevents linux v4.7 and before to be built with gcc-8.1.0 on armv7
targets.
$ arm-linux-gnueabihf-gcc -v
Using built-in specs.
COLLECT_GCC=arm-linux-gnueabihf-gcc
COLLECT_LTO_WRAPPER=/home/ed/gnu/arm-linux-gnueabihf-linux64/libexec/gcc/arm-linux-gnueabihf/8.1.0/lto-wrapper
Target: arm-linux-gnueabihf
Configured with: ../gcc-8.1.0/configure
--prefix=/home/ed/gnu/arm-linux-gnueabihf-linux64 --target=arm-linux-gnueabihf
--enable-languages=all --with-arch=armv7-a --with-tune=cortex-a9
--with-fpu=vfpv3-d16 --with-float=hard
Thread model: posix
gcc version 8.1.0 (GCC)
$ arm-linux-gnueabihf-gcc -save-temps -Os -c test.c
test.s: Assembler messages:
test.s:39: Error: .err encountered
in test.s we see, that __r2 is allocated in r3 but that is unexpected,
it should have been r2:
sys_oabi_sendmsg:
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
cmp r1, #0
bxeq lr
uxth r2, r2
cmp r2, #1
cmpeq r0, #0
bxne lr
mov r3, #0
str lr, [sp, #-4]!
ldr r3, [r3]
mov r0, r1
sub r1, r3, #1
mov r3, #110
.syntax divided
@ 37 "000.c" 1
.ifnc r0,r0; .ifnc r0r0,fpr11; .ifnc r0r0,r11fp; .ifnc r0r0,ipr12;
.ifnc r0r0,r12ip; .err; .endif; .endif; .endif; .endif; .endif
.ifnc r3,r2; .ifnc r3r2,fpr11; .ifnc r3r2,r11fp; .ifnc r3r2,ipr12;
.ifnc r3r2,r12ip; .err; .endif; .endif; .endif; .endif; .endif
.ifnc r1,r1; .ifnc r1r1,fpr11; .ifnc r1r1,r11fp; .ifnc r1r1,ipr12;
.ifnc r1r1,r12ip; .err; .endif; .endif; .endif; .endif; .endif
bl __put_user_4
@ 0 "" 2
.arm
.syntax unified
ldr pc, [sp], #4
The after v4.8 this macro was a bit simplified, and causes less register
pressure, but I think it works only by chance.
I am not sure if that is a wrong expectation or a compiler bug.
It would be fixed when __r2 is declared volatile for instance.
