-Revert parts of 84326 and 84411. Distinquishing between fixed and non-fixed

stack slots and giving them different PseudoSourceValue's did not fix the
problem of post-alloc scheduling miscompiling llvm itself.
- Apply Dan's conservative workaround by assuming any non fixed stack slots can
alias other memory locations. This means a load from spill slot #1 cannot 
move above a store of spill slot #2. 
- Enable post-alloc scheduling for x86 at optimization leverl Default and above.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84424 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/PseudoSourceValue.cpp

@@ -63,6 +63,8 @@ namespace {
 
     virtual bool isConstant(const MachineFrameInfo *MFI) const;
 
+    virtual bool isAliased() const;
+
     virtual void printCustom(raw_ostream &OS) const {
       OS << "FixedStack" << FI;
     }
@@ -89,6 +91,23 @@ bool PseudoSourceValue::isConstant(const MachineFrameInfo *) const {
   return false;
 }
 
+bool PseudoSourceValue::isAliased() const {
+  if (this == getStack() ||
+      this == getGOT() ||
+      this == getConstantPool() ||
+      this == getJumpTable())
+    return false;
+  llvm_unreachable("Unknown PseudoSourceValue!");
+  return true;
+}
+
 bool FixedStackPseudoSourceValue::isConstant(const MachineFrameInfo *MFI) const{
   return MFI && MFI->isImmutableObjectIndex(FI);
 }
+
+bool FixedStackPseudoSourceValue::isAliased() const{
+  // Negative frame indices are used for special things that don't
+  // appear in LLVM IR. Non-negative indices may be used for things
+  // like static allocas.
+  return FI >= 0;
+}