| Issue |
91569
|
| Summary |
[AggressiveInstCombine] Missed optimization: a reversed chain of contiguous unsigned icmps could be merged
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
FLZ101
|
Assuming the machine is little-endian, a reversed chain of contiguous unsigned icmps could be merged. For example,
```c
struct Foo {
unsigned short n;
unsigned char o;
unsigned char p;
};
int compare(struct Foo *f1, struct Foo *f2) {
if (f1->p > f2->p)
return 1;
if (f1->p < f2->p)
return -1;
if (f1->o > f2->o)
return 1;
if (f1->o < f2->o)
return -1;
if (f1->n > f2->n)
return 1;
if (f1->n < f2->n)
return -1;
return 0;
}
```
the function `compare()` could be transformed as below,
```c
int compare(struct Foo *f1, struct Foo *f2) {
unsigned int a = *(unsigned int *)&(f1->n);
unsigned int b = *(unsigned int *)&(f2->n);
return a > b ? 1 : a < b ? -1 : 0;
}
```
This kind of pattern is found in [velvet](https://github.com/dzerbino/velvet/tree/master) (a de novo genome assembler), more specificly the hot function `compareKmers()`.
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