add a little peephole optimization. This allows us to codegen:

int a(short i) {
        return i & 1;
}

as

_a:
        andi. r3, r3, 1
        blr

instead of:

_a:
        rlwinm r2, r3, 0, 16, 31
        andi. r3, r2, 1
        blr

on ppc.  It should also help the other risc targets.

llvm-svn: 21189

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 765ff1b758a..74e807ca826 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -766,6 +766,17 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
       if (!C2) return N2;         // X and 0 -> 0
       if (N2C->isAllOnesValue())
 	return N1;                // X and -1 -> X
+
+      // and (zero_extend_inreg x:16:32), 1 -> and x, 1
+      if (N1.getOpcode() == ISD::ZERO_EXTEND_INREG ||
+          N1.getOpcode() == ISD::SIGN_EXTEND_INREG) {
+        // If we are masking out the part of our input that was extended, just
+        // mask the input to the extension directly.
+        unsigned ExtendBits =
+          MVT::getSizeInBits(cast<MVTSDNode>(N1)->getExtraValueType());
+        if ((C2 & (~0ULL << ExtendBits)) == 0)
+          return getNode(ISD::AND, VT, N1.getOperand(0), N2);
+      }
       break;
     case ISD::OR:
       if (!C2)return N1;          // X or 0 -> X