[PATCH] D63675: [InstCombine] Simplify icmp ult/uge (shl %x, C2), C1 iff C1 is power of two -> icmp eq/ne (and %x, (lshr -C1, C2)), 0.

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/test/Transforms/InstCombine/shl-and-unsigned-cmp-const.ll:15-25
 define i1 @scalar_i8_shl_and_ult_const_1(i8 %x) {
 ; CHECK-LABEL: @scalar_i8_shl_and_ult_const_1(
-; CHECK-NEXT:    [[SHL:%.*]] = shl i8 [[X:%.*]], 5
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i8 [[SHL]], 64
+; CHECK-NEXT:    [[TMP1:%.*]] = and i8 [[X:%.*]], 6
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[TMP1]], 0
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %shl = shl i8 %x, 5
----------------
Why is this test so complicated?
```
  %shl = shl i8 %x, 5
  %cmp = icmp ult i8 %shl, 64
```
seems sufficient?
https://godbolt.org/z/GcVzPz


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63675/new/

https://reviews.llvm.org/D63675