https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103281
Bug ID: 103281
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
void foo(void);
static unsigned b;
int main() {
for (; b < 3; b++) {
char c = b;
char a = c ? c : c << 1;
if (!(a < 1 ^ b))
foo();
}
}
trunk cannot eliminate the call to foo but 11.2.0 can:
gcc-11.2.0 -O3 -S -o /dev/stdout case.c
main:
.LFB0:
.cfi_startproc
movl b(%rip), %eax
cmpl $2, %eax
ja .L6
testl %eax, %eax
movl $1, %edx
cmove %edx, %eax
.L8:
addl $1, %eax
movl %eax, b(%rip)
cmpl $2, %eax
je .L8
.L6:
xorl %eax, %eax
ret
.cfi_endproc
gcc-trunk -O3 -S -o /dev/stdout case.c
main:
.LFB0:
.cfi_startproc
movl b(%rip), %eax
cmpl $2, %eax
ja .L13
.p2align 4,,10
.p2align 3
.L12:
xorl %edx, %edx
testb %al, %al
setle %dl
cmpl %eax, %edx
je .L16
addl $1, %eax
movl %eax, b(%rip)
cmpl $3, %eax
jne .L12
.L13:
xorl %eax, %eax
ret
.p2align 4,,10
.p2align 3
.L16:
subq $8, %rsp
.cfi_def_cfa_offset 16
.L14:
call foo
movl b(%rip), %eax
addl $1, %eax
movl %eax, b(%rip)
cmpl $2, %eax
ja .L7
.L2:
xorl %edx, %edx
testb %al, %al
setle %dl
cmpl %eax, %edx
je .L14
addl $1, %eax
movl %eax, b(%rip)
cmpl $3, %eax
jne .L2
.L7:
xorl %eax, %eax
popq %rdx
.cfi_def_cfa_offset 8
ret
.cfi_endproc
gcc-trunk -v
Using built-in specs.
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20211116 (experimental) (GCC)
Started with
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=7d6979197274a662da7bdc564314afe8415865c1
