Use the new TargetLowering::ComputeNumSignBits method to eliminate
sign_extend_inreg operations. Though ComputeNumSignBits is still rudimentary,
this is enough to compile this:
short test(short X, short x) {
int Y = X+x;
return (Y >> 1);
}
short test2(short X, short x) {
int Y = (short)(X+x);
return Y >> 1;
}
into:
_test:
add r2, r3, r4
srawi r3, r2, 1
blr
_test2:
add r2, r3, r4
extsh r2, r2
srawi r3, r2, 1
blr
instead of:
_test:
add r2, r3, r4
srawi r2, r2, 1
extsh r3, r2
blr
_test2:
add r2, r3, r4
extsh r2, r2
srawi r2, r2, 1
extsh r3, r2
blr
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28146 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b967855..16ce87a 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1937,6 +1937,11 @@
SDOperand Truncate = DAG.getConstant(N0C->getValue(), EVT);
return DAG.getNode(ISD::SIGN_EXTEND, VT, Truncate);
}
+
+ // If the input is already sign extended, just drop the extend.
+ if (TLI.ComputeNumSignBits(N0) >= MVT::getSizeInBits(VT)-EVTBits+1)
+ return N0;
+
// fold (sext_in_reg (sext_in_reg x, VT2), VT1) -> (sext_in_reg x, minVT) pt1
if (N0.getOpcode() == ISD::SIGN_EXTEND_INREG &&
cast<VTSDNode>(N0.getOperand(1))->getVT() <= EVT) {
@@ -1947,11 +1952,6 @@
EVT < cast<VTSDNode>(N0.getOperand(1))->getVT()) {
return DAG.getNode(ISD::SIGN_EXTEND_INREG, VT, N0.getOperand(0), N1);
}
- // fold (sext_in_reg (assert_sext x)) -> (assert_sext x)
- if (N0.getOpcode() == ISD::AssertSext &&
- cast<VTSDNode>(N0.getOperand(1))->getVT() <= EVT) {
- return N0;
- }
// fold (sext_in_reg (sextload x)) -> (sextload x)
if (N0.getOpcode() == ISD::SEXTLOAD &&
cast<VTSDNode>(N0.getOperand(3))->getVT() <= EVT) {