Optimize exact sdiv by a constant power of 2 to ashr.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78714 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index b9b4ccb..798e3d2 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -3064,6 +3064,15 @@
// sdiv X, -1 == -X
if (RHS->isAllOnesValue())
return BinaryOperator::CreateNeg(*Context, Op0);
+
+ // sdiv X, C --> ashr X, log2(C)
+ if (cast<SDivOperator>(&I)->isExact() &&
+ RHS->getValue().isNonNegative() &&
+ RHS->getValue().isPowerOf2()) {
+ Value *ShAmt = llvm::ConstantInt::get(RHS->getType(),
+ RHS->getValue().exactLogBase2());
+ return BinaryOperator::CreateAShr(Op0, ShAmt, I.getName());
+ }
}
// If the sign bits of both operands are zero (i.e. we can prove they are