[AggressiveInstCombine] Fold split-width i32 cttz/ctlz patterns into wide i64 intrinsics (#192296)
This patch teaches `AggressiveInstCombine ` to recognize and fold common split-width i32 cttz/ctlz intrinsic calls into a single full-width i64
cttz/ctlz intrinsic.
For ex:
```
define i32 @src(i64 %val) {
%lo = trunc i64 %val to i32
%cmp = icmp eq i32 %lo, 0
%shr = lshr i64 %val, 32
%hi = trunc i64 %shr to i32
%cttz_hi = call i32 @llvm.cttz.i32(i32 %hi, i1 true)
%hi_plus32 = or i32 %cttz_hi, 32
%cttz_lo = call i32 @llvm.cttz.i32(i32 %lo, i1 true)
%result = select i1 %cmp, i32 %hi_plus32, i32 %cttz_lo
ret i32 %result
}
define i32 @tgt(i64 %val) {
%cttz64 = call i64 @llvm.cttz.i64(i64 %val, i1 false)
%result = trunc i64 %cttz64 to i32
ret i32 %result
}
```
and similarly for ctlz intrinsic.
Alive proof for the 2 folds added by this patch.
cttz:
https://alive2.llvm.org/ce/z/-s14-s
ctlz:
https://alive2.llvm.org/ce/z/WfQepH
3aed0816fe