fold trivial token factor nodes. This allows us to compile

test/CodeGen/X86/fp-stack-ret.ll into:

        movl 4(%esp), %eax
        fldl (%eax)
        ret

instead of:

        subl $12, %esp
        movl 16(%esp), %eax
        movsd (%eax), %xmm0
        movsd %xmm0, (%esp)
        fldl (%esp)
        addl $12, %esp
        ret

by eliminating a token factor that blocked a check.

llvm-svn: 34584

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -1351,6 +1351,12 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
 
   // Fold operations.
   switch (Opcode) {
+  case ISD::TokenFactor:
+    // Fold trivial token factors.
+    if (N1.getOpcode() == ISD::EntryToken) return N2;
+    if (N2.getOpcode() == ISD::EntryToken) return N1;
+    break;
+      
   case ISD::AND:
     // (X & 0) -> 0.  This commonly occurs when legalizing i64 values, so it's
     // worth handling here.