https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102879
Bug ID: 102879
Summary: [12 Regression] Dead Code Elimination Regression at
-O3
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
void foo(void);
static int b, c, d;
static char a(char e, int f) { return e < 0 ? e : e >> f; }
int main() {
c = 2;
for (int g = 0; g < 2; g++) {
for (int h = 0; h < 3; h++)
d = a(c, d == b);
if (!d)
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:
.LFB1:
.cfi_startproc
movl $2, c(%rip)
xorl %eax, %eax
movl $2, d(%rip)
ret
.cfi_endproc
gcc-trunk test.c -S -O3 -o /dev/stdout
...
main:
.LFB1:
.cfi_startproc
movl $2, %edx
pushq %rbx
.cfi_def_cfa_offset 16
.cfi_offset 3, -16
movl d(%rip), %ecx
movl $2, %ebx
movl $2, c(%rip)
movsbl %dl, %eax
testb %dl, %dl
js .L9
.L4:
testl %ecx, %ecx
movl %eax, %edx
sete %cl
sarl %cl, %edx
testl %edx, %edx
movl %eax, %edx
sete %cl
sarl %cl, %edx
testl %edx, %edx
sete %cl
sarl %cl, %eax
movl %eax, d(%rip)
testl %eax, %eax
jne .L5
call foo
.L5:
cmpl $1, %ebx
je .L3
.L10:
movl c(%rip), %edx
movl d(%rip), %ecx
movl $1, %ebx
movsbl %dl, %eax
testb %dl, %dl
jns .L4
.L9:
movl %eax, d(%rip)
cmpl $1, %ebx
jne .L10
.L3:
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 20211021 (experimental) (GCC)
Started with
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=2e96b5f14e4025691b57d2301d71aa6092ed44bc
