Make the case I just checked in stronger. Now we compile this:
short test2(short X, short x) {
int Y = (short)(X+x);
return Y >> 1;
}
to:
_test2:
add r2, r3, r4
extsh r2, r2
srawi r3, r2, 1
blr
instead of:
_test2:
add r2, r3, r4
extsh r2, r2
srwi r2, r2, 1
extsh r3, r2
blr
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28175 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 1515df5..de23285 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1948,17 +1948,25 @@
EVT < cast<VTSDNode>(N0.getOperand(1))->getVT()) {
return DAG.getNode(ISD::SIGN_EXTEND_INREG, VT, N0.getOperand(0), N1);
}
-
- // fold (sext_in_reg (srl X, 24), i8) -> sra X, 24
- if (N0.getOpcode() == ISD::SRL) {
- if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(N0.getOperand(1)))
- if (ShAmt->getValue()+EVTBits == MVT::getSizeInBits(VT))
- return DAG.getNode(ISD::SRA, VT, N0.getOperand(0), N0.getOperand(1));
- }
-
+
// fold (sext_in_reg x) -> (zext_in_reg x) if the sign bit is zero
if (TLI.MaskedValueIsZero(N0, 1ULL << (EVTBits-1)))
return DAG.getZeroExtendInReg(N0, EVT);
+
+ // fold (sext_in_reg (srl X, 24), i8) -> sra X, 24
+ // fold (sext_in_reg (srl X, 23), i8) -> sra X, 23 iff possible.
+ // We already fold "(sext_in_reg (srl X, 25), i8) -> srl X, 25" above.
+ if (N0.getOpcode() == ISD::SRL) {
+ if (ConstantSDNode *ShAmt = dyn_cast<ConstantSDNode>(N0.getOperand(1)))
+ if (ShAmt->getValue()+EVTBits <= MVT::getSizeInBits(VT)) {
+ // We can turn this into an SRA iff the input to the SRL is already sign
+ // extended enough.
+ unsigned InSignBits = TLI.ComputeNumSignBits(N0.getOperand(0));
+ if (MVT::getSizeInBits(VT)-(ShAmt->getValue()+EVTBits) < InSignBits)
+ return DAG.getNode(ISD::SRA, VT, N0.getOperand(0), N0.getOperand(1));
+ }
+ }
+
// fold (sext_inreg (extload x)) -> (sextload x)
if (N0.getOpcode() == ISD::EXTLOAD &&
EVT == cast<VTSDNode>(N0.getOperand(3))->getVT() &&