[PATCH] D157310: [ValueTracking] In `isKnownToBeAPowerOfTwo` an `i1` value is always true if `OrZero` is set

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n created this revision.
goldstein.w.n added reviewers: nikic, Allen.
Herald added subscribers: StephenFan, hiraditya.
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This is trivially true.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D157310

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
@@ -585,8 +585,7 @@
 ; CHECK-LABEL: define i16 @i1_is_pow2_or_zero
 ; CHECK-SAME: (i1 [[X:%.*]], i16 [[Y:%.*]]) {
 ; CHECK-NEXT:    [[XX:%.*]] = zext i1 [[X]] to i16
-; CHECK-NEXT:    [[YY:%.*]] = xor i16 [[XX]], [[Y]]
-; CHECK-NEXT:    [[R:%.*]] = call i16 @llvm.umax.i16(i16 [[YY]], i16 [[Y]])
+; CHECK-NEXT:    [[R:%.*]] = or i16 [[XX]], [[Y]]
 ; CHECK-NEXT:    ret i16 [[R]]
 ;
   %xx = zext i1 %x to i16
@@ -600,8 +599,7 @@
 ; CHECK-SAME: (i1 [[X:%.*]], i16 [[Y0:%.*]], i16 [[Z:%.*]]) {
 ; CHECK-NEXT:    [[XX:%.*]] = zext i1 [[X]] to i16
 ; CHECK-NEXT:    [[Y:%.*]] = or i16 [[Y0]], [[Z]]
-; CHECK-NEXT:    [[YY:%.*]] = xor i16 [[Y]], [[XX]]
-; CHECK-NEXT:    [[R:%.*]] = call i16 @llvm.umax.i16(i16 [[YY]], i16 [[Y]])
+; CHECK-NEXT:    [[R:%.*]] = or i16 [[Y]], [[XX]]
 ; CHECK-NEXT:    ret i16 [[R]]
 ;
   %xx = zext i1 %x to i16
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2016,6 +2016,10 @@
   if (isa<Constant>(V))
     return OrZero ? match(V, m_Power2OrZero()) : match(V, m_Power2());
 
+  // i1 is by definition a power of 2 or zero.
+  if (OrZero && V->getType()->getScalarSizeInBits() == 1)
+    return true;
+
   auto *I = dyn_cast<Instruction>(V);
   if (!I)
     return false;


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