| Issue |
114879
|
| Summary |
WRONG code: GVN? Loop opts?
|
| Labels |
miscompilation
|
| Assignees |
|
| Reporter |
JonPsson1
|
cat wrong0.i
```
int printf(const char *, ...);
unsigned int IntArr[6];
unsigned int GlobIntONE = 1, GlobIntZERO = 0;
const unsigned int *GlobIntPtr = 0;
unsigned long Res;
unsigned long *ResPtr = &Res;
const unsigned int **GlobIntPtrPTr = &GlobIntPtr;
unsigned int *func() {
int *GlobIntONEPtr = &GlobIntONE;
for (int Idx = 0; Idx <= 7; Idx += 1) {
int Idx2 = 1;
if (Idx > 0) {
for (; Idx2 <= 7; Idx2 += 1)
;
return GlobIntONEPtr;
}
}
0 != &GlobIntONEPtr;
return &GlobIntZERO;
}
int main() {
IntArr[GlobIntZERO] = GlobIntZERO;
*GlobIntPtrPTr = func();
unsigned char Byte = *GlobIntPtr;
*ResPtr = Byte;
printf("checksum = %X\n", Res);
}
```
In the above file, func() should obviously should return GlobIntONEPtr, but it does not if compiled with '-fno-inline -mllvm -unroll-full-max-count=1'.
```
clang -O0 -march=z16 wrong0.i -o a.out -w -fno-inline ; ./a.out
checksum = 1
clang -O3 -march=z16 wrong0.i -o a.out -w -fno-inline ; ./a.out
checksum = 1
clang -O3 -march=z16 wrong0.i -o a.out -w -fno-inline -mllvm -unroll-full-max-count=1 ; ./a.out
checksum = 0
```
It may be that GVN does something wrong, as after it @func() is always returning ptr undef. Or it could very well be some of the loop optimizations that is run just before it.
A bisect shows that
```
d77067d08a3f56dc2d0e6c95bd2852c943df743a is the first bad commit
commit d77067d08a3f56dc2d0e6c95bd2852c943df743a
Author: Nikita Popov <[email protected]>
Date: Wed Dec 6 14:17:18 2023 +0100
[ValueTracking] Add dominating condition support in computeKnownBits() (#73662)
```
@nikic
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