[PATCH] D145339: [InstCombine] Add transform `(icmp eq/ne bitreverse(x), C)` -> `(icmp eq/ne x, bitreverse(C))`

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n created this revision.
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EQ: https://alive2.llvm.org/ce/z/TESofr
NE: https://alive2.llvm.org/ce/z/mwloaT


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D145339

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/cmp-intrinsic.ll


Index: llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
===================================================================
--- llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
+++ llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
@@ -767,8 +767,7 @@
 
 define i1 @bitreverse_ne_22(i8 %x) {
 ; CHECK-LABEL: @bitreverse_ne_22(
-; CHECK-NEXT:    [[Y:%.*]] = call i8 @llvm.bitreverse.i8(i8 [[X:%.*]])
-; CHECK-NEXT:    [[Z:%.*]] = icmp ne i8 [[Y]], 22
+; CHECK-NEXT:    [[Z:%.*]] = icmp ne i8 [[X:%.*]], 104
 ; CHECK-NEXT:    ret i1 [[Z]]
 ;
   %y = call i8 @llvm.bitreverse.i8(i8 %x)
@@ -778,8 +777,7 @@
 
 define <2 x i1> @bitreverse_vec_eq_2_2(<2 x i8> %x) {
 ; CHECK-LABEL: @bitreverse_vec_eq_2_2(
-; CHECK-NEXT:    [[Y:%.*]] = call <2 x i8> @llvm.bitreverse.v2i8(<2 x i8> [[X:%.*]])
-; CHECK-NEXT:    [[Z:%.*]] = icmp eq <2 x i8> [[Y]], <i8 2, i8 2>
+; CHECK-NEXT:    [[Z:%.*]] = icmp eq <2 x i8> [[X:%.*]], <i8 64, i8 64>
 ; CHECK-NEXT:    ret <2 x i1> [[Z]]
 ;
   %y = call <2 x i8> @llvm.bitreverse.v2i8(<2 x i8> %x)
Index: llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3282,6 +3282,11 @@
     return new ICmpInst(Pred, II->getArgOperand(0),
                         ConstantInt::get(Ty, C.byteSwap()));
 
+  case Intrinsic::bitreverse:
+    // bitreverse(A) == C  ->  A == bitreverse(C)
+    return new ICmpInst(Pred, II->getArgOperand(0),
+                        ConstantInt::get(Ty, C.reverseBits()));
+
   case Intrinsic::ctlz:
   case Intrinsic::cttz: {
     // ctz(A) == bitwidth(A)  ->  A == 0 and likewise for !=


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