[llvm] e2079e8 - [InstCombine] Add transform `(icmp eq/ne bitreverse(x), C)` -> `(icmp eq/ne x, bitreverse(C))`

[Noah Goldstein via llvm-commits]

Author: Noah Goldstein
Date: 2023-03-06T20:29:34-06:00
New Revision: e2079e896aa1ac3a22521af95c031e0374668e07

URL: https://github.com/llvm/llvm-project/commit/e2079e896aa1ac3a22521af95c031e0374668e07
DIFF: https://github.com/llvm/llvm-project/commit/e2079e896aa1ac3a22521af95c031e0374668e07.diff

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

EQ: https://alive2.llvm.org/ce/z/TESofr
NE: https://alive2.llvm.org/ce/z/mwloaT

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D145339

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 1616c0e90ecc0..2eb96abd24fc8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3282,6 +3282,11 @@ Instruction *InstCombinerImpl::foldICmpEqIntrinsicWithConstant(
     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 !=

diff  --git a/llvm/test/Transforms/InstCombine/cmp-intrinsic.ll b/llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
index 171a06e1fea02..f2cecd34228d0 100644
--- a/llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
+++ b/llvm/test/Transforms/InstCombine/cmp-intrinsic.ll
@@ -767,8 +767,7 @@ define i1 @trunc_negative_destbits_not_enough(i33 %x) {
 
 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)
@@ -790,8 +789,7 @@ define i1 @bitreverse_ult_22_fail_not_equality_pred(i8 %x) {
 
 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)