| Issue |
98217
|
| Summary |
how to express pext without intrinsics or inline assembly
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
ImpleLee
|
I want to use x86-64 `pext`, but I also want my function to look platform-agnostic, so I don't want to use intrinsics or inline assembly.
I tried some semantic-equivalent implementations of `pext` I found online, but none of them can be compiled to `pext`.
Is it really possible to make the compiler generate the `pext` instruction? Or will there be any plan to support this behavior?
Here are the `pext` implementations I tried. ( https://godbolt.org/z/f3vMTf8ob )
```c++
// from https://stackoverflow.com/questions/21144237
int pext1(int x, int mask) {
int res = 0;
for(int bb = 1; mask != 0; bb += bb) {
if(x & mask & -mask) {
res |= bb;
}
mask &= (mask - 1);
}
return res;
}
// from https://www.felixcloutier.com/x86/pext
int pext2(int x, int mask) {
int res = 0;
int k = 0;
for (int m = 0; m < 32; ++m) {
if (mask & (1 << m)) {
res |= ((x >> m) & 1) << k;
k += 1;
}
}
return res;
}
```
![]()
_______________________________________________
llvm-bugs mailing list
llvm-bugs@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-bugs
