Another minor simplification: handle setcc (zero_extend x), c -> setcc(x, c')
llvm-svn: 21318
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index a52289f..fbadd63 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -406,6 +406,51 @@
case ISD::SETGE: return getConstant((int64_t)C1 >= (int64_t)C2, VT);
}
} else {
+ // If the LHS is a ZERO_EXTEND and if this is an ==/!= comparison, perform
+ // the comparison on the input.
+ if (N1.getOpcode() == ISD::ZERO_EXTEND) {
+ unsigned InSize = MVT::getSizeInBits(N1.getOperand(0).getValueType());
+
+ // If the comparison constant has bits in the upper part, the
+ // zero-extended value could never match.
+ if (C2 & (~0ULL << InSize)) {
+ unsigned VSize = MVT::getSizeInBits(N1.getValueType());
+ switch (Cond) {
+ case ISD::SETUGT:
+ case ISD::SETUGE:
+ case ISD::SETEQ: return getConstant(0, VT);
+ case ISD::SETULT:
+ case ISD::SETULE:
+ case ISD::SETNE: return getConstant(1, VT);
+ case ISD::SETGT:
+ case ISD::SETGE:
+ // True if the sign bit of C2 is set.
+ return getConstant((C2 & (1ULL << VSize)) != 0, VT);
+ case ISD::SETLT:
+ case ISD::SETLE:
+ // True if the sign bit of C2 isn't set.
+ return getConstant((C2 & (1ULL << VSize)) == 0, VT);
+ default:
+ break;
+ }
+ }
+
+ // Otherwise, we can perform the comparison with the low bits.
+ switch (Cond) {
+ case ISD::SETEQ:
+ case ISD::SETNE:
+ case ISD::SETUGT:
+ case ISD::SETUGE:
+ case ISD::SETULT:
+ case ISD::SETULE:
+ return getSetCC(Cond, VT, N1.getOperand(0),
+ getConstant(C2, N1.getOperand(0).getValueType()));
+ default:
+ break; // todo, be more careful with signed comparisons
+ }
+ }
+
+
uint64_t MinVal, MaxVal;
unsigned OperandBitSize = MVT::getSizeInBits(N2C->getValueType(0));
if (ISD::isSignedIntSetCC(Cond)) {