[PATCH] D64275: [InstCombine] Generalize InstCombiner::foldAndOrOfICmpsOfAndWithPow2().

[Huihui Zhang via Phabricator via llvm-commits]

huihuiz added inline comments.


================
Comment at: llvm/test/Transforms/InstCombine/onehot_merge.ll:246
 
 ; Should not fold
 define i1 @foo1_and_extra_use_and(i32 %k, i32 %c1, i32 %c2, i32* %p) {
----------------
lebedev.ri wrote:
> Looks like this one should?
I am OK with allowing 'and' to have more than one use.

Folding cut instruction count by 2, the worst case is no instruction count increase.


================
Comment at: llvm/test/Transforms/InstCombine/onehot_merge.ll:340
 
 ; Should not fold
 define i1 @foo1_and_extra_use_cmp2(i32 %k, i32 %c1, i32 %c2, i1* %p) {
----------------
lebedev.ri wrote:
> Could fold, no instruction count increase
We should not fold when 'cmp' has more than one use, this will increase instruction count when one side is using the new form.

Take this as an example, we need to keep the extra 'cmp' that can't be reused, while the benefit of folding is offset by the added signbit shift instruction.

```
define i1 @foo(i32 %k, i32 %c1, i32 %c2, i1* %p) {
  %t0 = shl i32 1, %c1
  %t1 = and i32 %t0, %k
  %t2 = icmp eq i32 %t1, 0
  store i1 %t2, i1* %p  ; extra use of cmp
  %t3 = shl i32 %k, %c2
  %t4 = icmp sgt i32 %t3, -1
  %or = or i1 %t2, %t4
  ret i1 %or
}

```


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D64275/new/

https://reviews.llvm.org/D64275