Add a transform to DAG Combiner. This improves the
code for the case where 32-bit divide by constant is
turned into 64-bit multiply by constant. 8771012.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122090 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index be5a5bc..522ebee 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3171,6 +3171,26 @@
DAG.getConstant(c1 + c2, N1.getValueType()));
}
+ // fold (srl (trunc (srl x, c1)), c2) -> 0 or (trunc (srl x, (add c1, c2)))
+ // This is only valid if the OpSizeInBits + c1 = size of inner shift
+ if (N1C && N0.getOpcode() == ISD::TRUNCATE &&
+ N0.getOperand(0).getOpcode() == ISD::SRL &&
+ N0.getOperand(0)->getOperand(1).getOpcode() == ISD::Constant) {
+ uint64_t c1 =
+ cast<ConstantSDNode>(N0.getOperand(0)->getOperand(1))->getZExtValue();
+ uint64_t c2 = N1C->getZExtValue();
+ EVT InnerShiftVT = N0.getOperand(0)->getOperand(1).getValueType();
+ uint64_t InnerShiftSize = InnerShiftVT.getScalarType().getSizeInBits();
+ if (c1 + OpSizeInBits == InnerShiftSize) {
+ if (c1 + c2 >= InnerShiftSize)
+ return DAG.getConstant(0, VT);
+ return DAG.getNode(ISD::TRUNCATE, N0->getDebugLoc(), VT,
+ DAG.getNode(ISD::SRL, N0->getDebugLoc(), InnerShiftVT,
+ N0.getOperand(0)->getOperand(0),
+ DAG.getConstant(c1 + c2, InnerShiftVT)));
+ }
+ }
+
// fold (srl (shl x, c), c) -> (and x, cst2)
if (N1C && N0.getOpcode() == ISD::SHL && N0.getOperand(1) == N1 &&
N0.getValueSizeInBits() <= 64) {