https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114206
Bug ID: 114206
Summary: GCC generates wrong-code
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: congli at smail dot nju.edu.cn
Target Milestone: ---
The program shown below presents a wrong code bug, where the correct results
should be "f(0, NULL) = 0" while `-Os -fno-tree-ccp -fno-tree-copy-prop
-fno-tree-forwprop -fno-tree-fre -fno-tree-vrp` prints "f(0, NULL) = 1".
```
#include <stdio.h>
int f(int t, const int *a) {
const int b[4] = {0};
if (t == 0) {
return f(1, b);
} else {
return b == a;
}
}
int main(void) {
printf("f(0, NULL) = %d\n", f(0, NULL));
}
```
Compiler Explorer: https://gcc.godbolt.org/z/W164xWMrP
We checked the assembly, finding that it is weird that the compiler generates a
`cmove` instruction. See explanations below:
```
f:
leaq -16(%rsp), %rax -> RAX = RSP-16
testl %edi, %edi -> we called f(0, NULL); %edi = 0, ZF = 1
cmove %rax, %rsi -> condition fulfilled; RSI=RAX=RSP-16; weird
generation
cmpq %rax, %rsi -> RSI=RAX; ZF=1
sete %al -> AL = 1
movzbl %al, %eax -> EAX = 1 (error)
ret
```
