Reapply bottom-up fast-isel, with several fixes for x86-32:

- Check getBytesToPopOnReturn().
 - Eschew ST0 and ST1 for return values.
 - Fix the PIC base register initialization so that it doesn't ever
   fail to end up the top of the entry block.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108039 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp

@@ -82,6 +82,13 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf) {
   MF = &mf;
   RegInfo = &MF->getRegInfo();
 
+  // Check whether the function can return without sret-demotion.
+  SmallVector<ISD::OutputArg, 4> Outs;
+  GetReturnInfo(Fn->getReturnType(),
+                Fn->getAttributes().getRetAttributes(), Outs, TLI);
+  CanLowerReturn = TLI.CanLowerReturn(Fn->getCallingConv(), Fn->isVarArg(),
+                                      Outs, Fn->getContext());
+
   // Create a vreg for each argument register that is not dead and is used
   // outside of the entry block for the function.
   for (Function::const_arg_iterator AI = Fn->arg_begin(), E = Fn->arg_end();
@@ -174,6 +181,7 @@ void FunctionLoweringInfo::clear() {
 #endif
   LiveOutRegInfo.clear();
   ArgDbgValues.clear();
+  RegFixups.clear();
 }
 
 /// CreateReg - Allocate a single virtual register for the given type.