https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104526
Bug ID: 104526
Summary: [12 Regression] Dead Code Elimination Regression at
-O3 (trunk vs. 11.2.0)
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: theodort at inf dot ethz.ch
Target Milestone: ---
cat case.c #138750
void foo(void);
static int a, b = 1, *c = &b;
int main() {
for (; a; a--) {
int d = 2 >> (1 / *c);
if (!d)
foo();
}
}
gcc-58aeb75d4097010ad9bb72b964265b18ab284f93 (trunk) -O3 can not eliminate foo
but gcc-11.2.0 -O3 can.
gcc-58aeb75d4097010ad9bb72b964265b18ab284f93 (trunk) -O3 -S -o /dev/stdout
case.c
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
movl a(%rip), %eax
testl %eax, %eax
je .L12
pushq %rbx
.cfi_def_cfa_offset 16
.cfi_offset 3, -16
xorl %ebx, %ebx
.L2:
movl b(%rip), %ecx
leal 1(%rcx), %eax
cmpl $2, %eax
movl $2, %eax
cmova %ebx, %ecx
sarl %cl, %eax
testl %eax, %eax
je .L3
movl $0, a(%rip)
.L10:
xorl %eax, %eax
popq %rbx
.cfi_remember_state
.cfi_def_cfa_offset 8
ret
.p2align 4,,10
.p2align 3
.L3:
.cfi_restore_state
call foo
subl $1, a(%rip)
jne .L2
jmp .L10
.L12:
.cfi_def_cfa_offset 8
.cfi_restore 3
xorl %eax, %eax
ret
---------- END OUTPUT ---------
gcc-11.2.0 -O3 -S -o /dev/stdout case.c
--------- OUTPUT ---------
main:
.LFB0:
.cfi_startproc
movl a(%rip), %eax
testl %eax, %eax
je .L2
movl $0, a(%rip)
.L2:
xorl %eax, %eax
ret
---------- END OUTPUT ---------
Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=c2b610e7c6c89fd422c5c31f01023bcddf3cf4a5
----- Build information -----
----- 58aeb75d4097010ad9bb72b964265b18ab284f93 (trunk)
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.1 20220213 (experimental) (GCC)
----- releases/gcc-11.2.0
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (GCC)
