[llvm] bab8058 - [ValueTracking] If `OrZero` is set, look through `trunc` in `isKnownToBePowerOfTwo`

[Noah Goldstein via llvm-commits]

Author: Noah Goldstein
Date: 2023-08-09T14:42:54-05:00
New Revision: bab8058d3b00b341e74ce91dc84c2c73b0ceb261

URL: https://github.com/llvm/llvm-project/commit/bab8058d3b00b341e74ce91dc84c2c73b0ceb261
DIFF: https://github.com/llvm/llvm-project/commit/bab8058d3b00b341e74ce91dc84c2c73b0ceb261.diff

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

Just move coverage.

Proof: https://alive2.llvm.org/ce/z/H37tVX

Differential Revision: https://reviews.llvm.org/D157304

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 652b1e8b653a41..794c1100a017be 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2036,6 +2036,8 @@ bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth,
   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);

diff  --git a/llvm/test/Analysis/ValueTracking/known-power-of-two.ll b/llvm/test/Analysis/ValueTracking/known-power-of-two.ll
index 90dec875fb90eb..1936e009e44568 100644
--- a/llvm/test/Analysis/ValueTracking/known-power-of-two.ll
+++ b/llvm/test/Analysis/ValueTracking/known-power-of-two.ll
@@ -36,7 +36,8 @@ define i8 @trunc_is_pow2_or_zero(i16 %x, i8 %y) {
 ; 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