[PATCH] D157304: [ValueTracking] If `OrZero` is set, look through `trunc` in `isKnownToBePowerOfTwo`

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n updated this revision to Diff 548698.
goldstein.w.n added a comment.

Rebase


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D157304/new/

https://reviews.llvm.org/D157304

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
@@ -36,7 +36,8 @@
 ; CHECK-SAME: (i16 [[X:%.*]], i8 [[Y:%.*]]) {
 ; CHECK-NEXT:    [[XP2:%.*]] = shl i16 4, [[X]]
 ; CHECK-NEXT:    [[XX:%.*]] = trunc i16 [[XP2]] to i8
-; CHECK-NEXT:    [[R:%.*]] = urem i8 [[Y]], [[XX]]
+; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[XX]], -1
+; CHECK-NEXT:    [[R:%.*]] = and i8 [[TMP1]], [[Y]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %xp2 = shl i16 4, %x
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2036,6 +2036,8 @@
   switch (I->getOpcode()) {
   case Instruction::ZExt:
     return isKnownToBeAPowerOfTwo(I->getOperand(0), OrZero, Depth, Q);
+  case Instruction::Trunc:
+    return OrZero && isKnownToBeAPowerOfTwo(I->getOperand(0), OrZero, Depth, Q);
   case Instruction::Shl:
     if (OrZero || Q.IIQ.hasNoUnsignedWrap(I) || Q.IIQ.hasNoSignedWrap(I))
       return isKnownToBeAPowerOfTwo(I->getOperand(0), OrZero, Depth, Q);


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