ScheduleDAGInstrs: In functions with tail calls PseudoSourceValues are not non-aliasing distinct objects

The code that builds the dependence graph assumes that two PseudoSourceValues
don't alias. In a tail calling function two FixedStackObjects might refer to the
same location. Worse 'immutable' fixed stack objects like function arguments are
not immutable and will be clobbered.

Change this so that a load from a FixedStackObject is not invariant in a tail
calling function and don't return a PseudoSourceValue for an instruction in tail
calling functions when building the dependence graph so that we handle function
arguments conservatively.

Fix for PR23459.

rdar://20740035

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236916 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/PowerPC/PPCISelLowering.cpp

@@ -4215,6 +4215,7 @@ PPCTargetLowering::FinishCall(CallingConv::ID CallConv, SDLoc dl,
             isa<ConstantSDNode>(Callee)) &&
     "Expecting an global address, external symbol, absolute value or register");
 
+    MF.getFrameInfo()->setHasTailCall();
     return DAG.getNode(PPCISD::TC_RETURN, dl, MVT::Other, Ops);
   }