https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102648
Bug ID: 102648
Summary: 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 int b, c, d = 40000;
static short e;
unsigned char f = 1;
static short a(short f, short g) { return f * g; }
int main() {
for (; e; e++) {
c = 0;
while (c - 1)
if (a(d, !f) > 1)
foo();
}
return 0;
}
11.2.0 at -O3 can eliminate the call to foo but trunk at -O3 cannot:
gcc-11 -v
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)
gcc-11 -O3 case.c -S -o /dev/stdout
...
main:
.LFB1:
.cfi_startproc
cmpw $0, e(%rip)
je .L2
movl $0, c(%rip)
.L3:
jmp .L3
.p2align 4,,10
.p2align 3
.L2:
xorl %eax, %eax
ret
gcc-trunk -v
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 12.0.0 20211008 (experimental) (GCC)
gcc-trunk -O3 case.c -S -o /dev/stdout
...
main:
.LFB1:
.cfi_startproc
cmpw $0, e(%rip)
movzbl f(%rip), %edx
je .L12
subq $8, %rsp
.cfi_def_cfa_offset 16
.p2align 4,,10
.p2align 3
.L5:
movl $0, c(%rip)
xorl %eax, %eax
testb %dl, %dl
sete %al
imulw $-25536, %ax, %ax
cmpw $1, %ax
jg .L15
.L3:
.L10:
jmp .L10
.p2align 4,,10
.p2align 3
.L15:
call foo
cmpl $1, c(%rip)
movzbl f(%rip), %edx
jne .L3
addw $1, e(%rip)
jne .L5
xorl %eax, %eax
addq $8, %rsp
.cfi_def_cfa_offset 8
ret
.L12:
xorl %eax, %eax
ret
704e8a825c78b9a8424c291509413bbb48e602c7 introduced this regression
