Chris prefers icmp/select over udiv!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60187 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 661b047..9214b6b 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2882,13 +2882,21 @@
if (Instruction *Common = commonIDivTransforms(I))
return Common;
- // X udiv C^2 -> X >> C
- // Check to see if this is an unsigned division with an exact power of 2,
- // if so, convert to a right shift.
if (ConstantInt *C = dyn_cast<ConstantInt>(Op1)) {
+ // X udiv C^2 -> X >> C
+ // Check to see if this is an unsigned division with an exact power of 2,
+ // if so, convert to a right shift.
if (C->getValue().isPowerOf2()) // 0 not included in isPowerOf2
return BinaryOperator::CreateLShr(Op0,
ConstantInt::get(Op0->getType(), C->getValue().logBase2()));
+
+ // X udiv C, where C >= signbit
+ if (C->getValue().isNegative()) {
+ Value *IC = InsertNewInstBefore(new ICmpInst(ICmpInst::ICMP_ULT, Op0, C),
+ I);
+ return SelectInst::Create(IC, Constant::getNullValue(I.getType()),
+ ConstantInt::get(I.getType(), 1));
+ }
}
// X udiv (C1 << N), where C1 is "1<<C2" --> X >> (N+C2)