https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105086
Bug ID: 105086
Summary: Dead Code Elimination Regression at -Os (trunk vs.
11.2.0) 25
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: yann at ywg dot ch
Target Milestone: ---
Created attachment 52702
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52702&action=edit
The case presented.
cat case.c #25
void foo();
int main() {
unsigned a = -23;
for (; a >= 2; ++a)
if (a == 55)
foo();
}
`gcc-0127fb1b78a36a7b228d4b3fe32eedfc8d273363 (trunk) -Os` can not eliminate
`foo` but `gcc-releases/gcc-11.2.0 -Os` can.
`gcc-0127fb1b78a36a7b228d4b3fe32eedfc8d273363 (trunk) -Os -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
movl $-23, %eax
.L6:
cmpl $55, %eax
je .L10
incl %eax
jne .L6
xorl %eax, %eax
ret
.L10:
pushq %rax
.cfi_def_cfa_offset 16
.L7:
xorl %eax, %eax
call foo
movl $56, %eax
.L2:
incl %eax
je .L12
cmpl $55, %eax
jne .L2
jmp .L7
.L12:
xorl %eax, %eax
popq %rdx
.cfi_def_cfa_offset 8
ret
---------- END OUTPUT ---------
`gcc-releases/gcc-11.2.0 -Os -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
xorl %eax, %eax
ret
---------- END OUTPUT ---------
Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=502ffb1f389011b28ee51815242c7397790802d5
----- Build information -----
----- 0127fb1b78a36a7b228d4b3fe32eedfc8d273363 (trunk)
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++
--prefix=/zdata/compiler_cache/gcc-0127fb1b78a36a7b228d4b3fe32eedfc8d273363
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.1 20220328 (experimental) (GCC)
----- releases/gcc-11.2.0
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++
--prefix=/zdata/compiler_cache/gcc-01a9836c07053b3286b2259d6b628c7583413f55
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (GCC)
