[PATCH] D157306: [ValueTracking] Add support for `bswap` and `bitreverse` in `isKnownToBeAPowerOfTwo`

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n updated this revision to Diff 547889.
goldstein.w.n added a comment.

Rebase


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D157306/new/

https://reviews.llvm.org/D157306

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Analysis/ValueTracking/known-power-of-two.ll


Index: llvm/test/Analysis/ValueTracking/known-power-of-two.ll
===================================================================
--- llvm/test/Analysis/ValueTracking/known-power-of-two.ll
+++ llvm/test/Analysis/ValueTracking/known-power-of-two.ll
@@ -84,7 +84,8 @@
 ; CHECK-SAME: (i16 [[X:%.*]], i16 [[Y:%.*]]) {
 ; CHECK-NEXT:    [[XP2:%.*]] = shl i16 4, [[X]]
 ; CHECK-NEXT:    [[XX:%.*]] = call i16 @llvm.bswap.i16(i16 [[XP2]])
-; CHECK-NEXT:    [[R:%.*]] = urem i16 [[Y]], [[XX]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i16 [[XX]], -1
+; CHECK-NEXT:    [[R:%.*]] = and i16 [[TMP1]], [[Y]]
 ; CHECK-NEXT:    ret i16 [[R]]
 ;
   %xp2 = shl i16 4, %x
@@ -115,7 +116,7 @@
 ; CHECK-NEXT:    [[XP2:%.*]] = shl nuw i16 1, [[X]]
 ; CHECK-NEXT:    [[XX:%.*]] = call i16 @llvm.bswap.i16(i16 [[XP2]])
 ; CHECK-NEXT:    [[AND:%.*]] = and i16 [[XX]], [[Y]]
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i16 [[AND]], [[XX]]
+; CHECK-NEXT:    [[R:%.*]] = icmp ne i16 [[AND]], 0
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
   %xp2 = shl i16 1, %x
@@ -148,7 +149,8 @@
 ; CHECK-SAME: (i16 [[X:%.*]], i16 [[Y:%.*]]) {
 ; CHECK-NEXT:    [[XP2:%.*]] = shl i16 4, [[X]]
 ; CHECK-NEXT:    [[XX:%.*]] = call i16 @llvm.bitreverse.i16(i16 [[XP2]])
-; CHECK-NEXT:    [[R:%.*]] = urem i16 [[Y]], [[XX]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add nsw i16 [[XX]], -1
+; CHECK-NEXT:    [[R:%.*]] = and i16 [[TMP1]], [[Y]]
 ; CHECK-NEXT:    ret i16 [[R]]
 ;
   %xp2 = shl i16 4, %x
@@ -179,7 +181,7 @@
 ; CHECK-NEXT:    [[XP2:%.*]] = shl nuw i16 1, [[X]]
 ; CHECK-NEXT:    [[XX:%.*]] = call i16 @llvm.bitreverse.i16(i16 [[XP2]])
 ; CHECK-NEXT:    [[AND:%.*]] = and i16 [[XX]], [[Y]]
-; CHECK-NEXT:    [[R:%.*]] = icmp eq i16 [[AND]], [[XX]]
+; CHECK-NEXT:    [[R:%.*]] = icmp ne i16 [[AND]], 0
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
   %xp2 = shl i16 1, %x
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2139,6 +2139,11 @@
       case Intrinsic::smin:
         return isKnownToBeAPowerOfTwo(II->getArgOperand(1), OrZero, Depth, Q) &&
                isKnownToBeAPowerOfTwo(II->getArgOperand(0), OrZero, Depth, Q);
+      // bswap/bitreverse just move around bits, but don't change any 1s/0s
+      // thus dont change pow2/non-pow2 status.
+      case Intrinsic::bitreverse:
+      case Intrinsic::bswap:
+        return isKnownToBeAPowerOfTwo(II->getArgOperand(0), OrZero, Depth, Q);
       default:
         break;
       }


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