https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102892
Bug ID: 102892
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
static long b[2][1] = {0};
void bar(void);
void foo(void);
int main() {
long c = 0;
for (long a; a < 1; ++a)
for (; c <= 1; c++) {
bar();
if (1 == b[c][0])
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
subq $8, %rsp
.cfi_def_cfa_offset 16
call bar
call bar
xorl %eax, %eax
addq $8, %rsp
.cfi_def_cfa_offset 8
ret
.cfi_endproc
gcc-trunk-O3 -S test.c -o /dev/stdout
main:
.LFB0:
.cfi_startproc
pushq %rbx
.cfi_def_cfa_offset 16
.cfi_offset 3, -16
xorl %ebx, %ebx
call bar
cmpq $1, b(,%rbx,8)
je .L11
.p2align 4,,10
.p2align 3
.L3:
cmpq $1, %rbx
je .L12
.L5:
call bar
movl $1, %ebx
cmpq $1, b(,%rbx,8)
jne .L3
.L11:
call foo
cmpq $1, %rbx
jne .L5
.L12:
xorl %eax, %eax
popq %rbx
.cfi_def_cfa_offset 8
ret
.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=01b5038718056b024b370b74a874fbd92c5bbab3
