[InstCombine] Teach getDemandedBitsLHSMask to handle constant splat vectors

This replaces a ConstantInt dyn_cast with m_APInt

Differential Revision: https://reviews.llvm.org/D38100

llvm-svn: 313840

1 files changed, 7 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 90b98dd71ae..1f981720ad1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3926,26 +3926,22 @@ static APInt getDemandedBitsLHSMask(ICmpInst &I, unsigned BitWidth,
   if (isSignCheck)
     return APInt::getSignMask(BitWidth);
 
-  ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand(1));
-  if (!CI) return APInt::getAllOnesValue(BitWidth);
-  const APInt &RHS = CI->getValue();
+  const APInt *RHS;
+  if (!match(I.getOperand(1), m_APInt(RHS)))
+    return APInt::getAllOnesValue(BitWidth);
 
   switch (I.getPredicate()) {
   // For a UGT comparison, we don't care about any bits that
   // correspond to the trailing ones of the comparand.  The value of these
   // bits doesn't impact the outcome of the comparison, because any value
   // greater than the RHS must differ in a bit higher than these due to carry.
-  case ICmpInst::ICMP_UGT: {
-    unsigned trailingOnes = RHS.countTrailingOnes();
-    return APInt::getBitsSetFrom(BitWidth, trailingOnes);
-  }
+  case ICmpInst::ICMP_UGT:
+    return APInt::getBitsSetFrom(BitWidth, RHS->countTrailingOnes());
 
   // Similarly, for a ULT comparison, we don't care about the trailing zeros.
   // Any value less than the RHS must differ in a higher bit because of carries.
-  case ICmpInst::ICMP_ULT: {
-    unsigned trailingZeros = RHS.countTrailingZeros();
-    return APInt::getBitsSetFrom(BitWidth, trailingZeros);
-  }
+  case ICmpInst::ICMP_ULT:
+    return APInt::getBitsSetFrom(BitWidth, RHS->countTrailingZeros());
 
   default:
     return APInt::getAllOnesValue(BitWidth);