Compile this:
short test4(unsigned X) {
return (X >> 16);
}
to:
_test4:
movl 4(%esp), %eax
sarl $16, %eax
ret
instead of:
_test4:
movl $-65536, %eax
andl 4(%esp), %eax
sarl $16, %eax
ret
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28171 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 9c469b5..e90f902 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1575,6 +1575,11 @@
}
}
+ // Simplify, based on bits shifted out of the LHS.
+ if (N1C && SimplifyDemandedBits(SDOperand(N, 0)))
+ return SDOperand(N, 0);
+
+
// If the sign bit is known to be zero, switch this to a SRL.
if (TLI.MaskedValueIsZero(N0, MVT::getIntVTSignBit(VT)))
return DAG.getNode(ISD::SRL, VT, N0, N1);