| Issue |
143622
|
| Summary |
Missed optimization: Reassociate multiplies by constants to shrink said constants
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
Alcaro
|
```c
int a(int b, int c, int d, int e)
{
return b*1000+c*100+d*10+e;
}
int a2(int b, int c, int d, int e)
{
return ((b*10+c)*10+d)*10+e;
}
```
Expected: Same for both.
Actual: a2 is a series of lea, as expected, but former contains two imul.
GCC also misses this optimization, but MSVC performs it. https://godbolt.org/z/1fs9xhsdb
The missed optimization also shows up on ARM and RISC-V, where a loads three different constants, but a2 reuses the same one. https://godbolt.org/z/qzMEv1b8j https://godbolt.org/z/bTYzY4vGa (and GCC optimizes mul by 10 to some shifts and adds, but that's a separate missed optimization)
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