Minor cleanup related to my latest scheduler changes.

[oota-llvm.git] / lib / Transforms / InstCombine / InstCombineShifts.cpp

diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp
index 27716b886a22694b4df85754e2d22d1083d7635f..a0c5ef5338f68e054715ad84d3c43e0630f8c9c4 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -53,6 +53,19 @@ Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) {
   if (ConstantInt *CUI = dyn_cast<ConstantInt>(Op1))
     if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I))
       return Res;
+
+  // X shift (A srem B) -> X shift (A and B-1) iff B is a power of 2.
+  // Because shifts by negative values are undefined.
+  if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op1))
+    if (BO->hasOneUse() && BO->getOpcode() == Instruction::SRem)
+      if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->getOperand(1)))
+        if (CI->getValue().isPowerOf2()) {
+          Constant *C = ConstantInt::get(BO->getType(), CI->getValue()-1);
+          Value *Rem = Builder->CreateAnd(BO->getOperand(0), C, BO->getName());
+          I.setOperand(1, Rem);
+          return &I;
+        }
+
   return 0;
 }
 
@@ -131,9 +144,9 @@ static bool CanEvaluateShifted(Value *V, unsigned NumBits, bool isLeftShift,
     // We can turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but it isn't
     // profitable unless we know the and'd out bits are already zero.
     if (CI->getZExtValue() > NumBits) {
-      unsigned HighBits = CI->getZExtValue() - NumBits;
+      unsigned LowBits = TypeWidth - CI->getZExtValue();
       if (MaskedValueIsZero(I->getOperand(0),
-                            APInt::getHighBitsSet(TypeWidth, HighBits)))
+                       APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits))
         return true;
     }
       
@@ -157,7 +170,7 @@ static bool CanEvaluateShifted(Value *V, unsigned NumBits, bool isLeftShift,
     if (CI->getZExtValue() > NumBits) {
       unsigned LowBits = CI->getZExtValue() - NumBits;
       if (MaskedValueIsZero(I->getOperand(0),
-                            APInt::getLowBitsSet(TypeWidth, LowBits)))
+                          APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits))
         return true;
     }