https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102895
Bug ID: 102895
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 test.c
master
static int a, b, c;
void foo(void);
int main() {
for (a = 0; a <= 1; ++a)
if (c <= a) {
for (b = 0; b <= 1; ++b)
;
} else
foo();
}
11.2.0 at -O3 can eliminate the call to foo but trunk at -O3 cannot:
gcc-11 -O3 -S test.c -o /dev/stdout
...
main:
.LFB0:
.cfi_startproc
xorl %eax, %eax
.p2align 4,,10
.p2align 3
.L2:
movl $2, b(%rip)
addl $1, %eax
movl %eax, a(%rip)
cmpl $1, %eax
je .L2
xorl %eax, %eax
ret
.cfi_endproc
gcc-trunk -O3 -S test.c -o /dev/stdout
...
main:
.LFB0:
.cfi_startproc
subq $8, %rsp
.cfi_def_cfa_offset 16
xorl %eax, %eax
movl $0, a(%rip)
.p2align 4,,10
.p2align 3
.L5:
testl %eax, %eax
jns .L9
call foo
.p2align 4,,10
.p2align 3
.L7:
movl a(%rip), %eax
addl $1, %eax
movl %eax, a(%rip)
cmpl $1, %eax
jle .L5
xorl %eax, %eax
addq $8, %rsp
.cfi_remember_state
.cfi_def_cfa_offset 8
ret
.p2align 4,,10
.p2align 3
.L9:
.cfi_restore_state
movl $2, b(%rip)
jmp .L7
.cfi_endproc
gcc-trunk -v
Using built-in specs.
Target: x86_64-pc-linux-gnu
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.0.0 20211022 (experimental) (GCC)
Introduced with
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=d8e1f1d24179690fd9c0f63c27b12e030010d9ea
