Handle 'lshr' instruction with SCEVUDiv object.

Comment the xor %x, -1 case.

llvm-svn: 53167

1 files changed, 14 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index d615c752b04..4462986f15b 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -1742,12 +1742,14 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
     }
     break;
   case Instruction::Xor:
-    // If the RHS of the xor is a signbit, then this is just an add.
-    // Instcombine turns add of signbit into xor as a strength reduction step.
     if (ConstantInt *CI = dyn_cast<ConstantInt>(U->getOperand(1))) {
+      // If the RHS of the xor is a signbit, then this is just an add.
+      // Instcombine turns add of signbit into xor as a strength reduction step.
       if (CI->getValue().isSignBit())
         return SE.getAddExpr(getSCEV(U->getOperand(0)),
                              getSCEV(U->getOperand(1)));
+
+      // If the RHS of xor is -1, then this is a not operation.
       else if (CI->isAllOnesValue())
         return SE.getNotSCEV(getSCEV(U->getOperand(0)));
     }
@@ -1763,6 +1765,16 @@ SCEVHandle ScalarEvolutionsImpl::createSCEV(Value *V) {
     }
     break;
 
+  case Instruction::LShr:
+    // Turn logical shift right of a constant into a unsigned divide.
+    if (ConstantInt *SA = dyn_cast<ConstantInt>(U->getOperand(1))) {
+      uint32_t BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
+      Constant *X = ConstantInt::get(
+        APInt(BitWidth, 1).shl(SA->getLimitedValue(BitWidth)));
+      return SE.getUDivExpr(getSCEV(U->getOperand(0)), getSCEV(X));
+    }
+    break;
+
   case Instruction::Trunc:
     return SE.getTruncateExpr(getSCEV(U->getOperand(0)), U->getType());