| Issue |
56046
|
| Summary |
Dead Code Elimination Regression at -O3 (trunk vs. 14.0.4)
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
thetheodor
|
```c
static short a;
static int b;
void foo(void);
void bar9_(void);
int main() {
char c;
b = a = 23;
for (; b <= 1;)
a = 1;
bar9_();
c = a >= 18 || 2 > 2 >> a ? 1 : 1 << a;
if (c == 0)
foo();
}
```
`llvm-4c2bccfda3892ae13e97b6bfdbc99ec8cf5d095d (trunk) -O3` can not eliminate `foo` but `llvm-llvmorg-14.0.4 -O3` can.
Target: `x86_64-unknown-linux-gnu`
------------------------------------------------
`llvm-4c2bccfda3892ae13e97b6bfdbc99ec8cf5d095d (trunk) -O3 [-emit-llvm] -S -o /dev/stdout case.c`
<details ><summary>Reduced assembly</summary><p>
```asm
main: # @main
.cfi_startproc
# %bb.0:
pushq %rax
.cfi_def_cfa_offset 16
movb $1, a(%rip)
callq bar9_@PLT
xorl %eax, %eax
cmpb $0, a(%rip)
movl $23, %ecx
cmovel %eax, %ecx
movl $2, %eax
shrl %cl, %eax
addl $-8, %ecx
cmpw $9, %cx
ja .LBB0_3
# %bb.1:
cmpl $2, %eax
jb .LBB0_3
# %bb.2:
callq foo@PLT
.LBB0_3:
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
retq
.Lfunc_end0:
.size main, .Lfunc_end0-main
```
</p></details>
------------------------------------------------
`llvm-llvmorg-14.0.4 -O3 [-emit-llvm] -S -o /dev/stdout case.c`
<details ><summary>Reduced assembly</summary><p>
```asm
main: # @main
.cfi_startproc
# %bb.0:
pushq %rax
.cfi_def_cfa_offset 16
movb $1, a(%rip)
callq bar9_
xorl %eax, %eax
popq %rcx
.cfi_def_cfa_offset 8
retq
.Lfunc_end0:
.size main, .Lfunc_end0-main
```
</p></details>
------------------------------------------------
### Bisection
Bisected to: c0e06c7448a2dd16796e210a66de68f269363e31
Committed by: @nikic
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