Disable the use of TBAA when using AA in CodeGen

There are currently two issues, of which I currently know, that prevent TBAA
from being correctly usable in CodeGen:

  1. Stack coloring does not update TBAA when merging allocas. This is easy
     enough to fix, but is not the largest problem.

  2. CGP inserts ptrtoint/inttoptr pairs when sinking address computations.
     Because BasicAA does not handle inttoptr, we'll often miss basic type punning
     idioms that we need to catch so we don't miscompile real-world code (like LLVM).

I don't yet have a small test case for this, but this fixes self hosting a
non-asserts build of LLVM on PPC64 when using -enable-aa-sched-mi and -misched=shuffle.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200093 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/StackColoring.cpp

@@ -553,6 +553,13 @@ void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
         if (!V)
           continue;
 
+        // FIXME: In order to enable the use of TBAA when using AA in CodeGen,
+        // we'll also need to update the TBAA nodes in MMOs with values
+        // derived from the merged allocas. When doing this, we'll need to use
+        // the same variant of GetUnderlyingObjects that is used by the
+        // instruction scheduler (that can look through ptrtoint/inttoptr
+        // pairs).
+
         // We've replaced IR-level uses of the remapped allocas, so we only
         // need to replace direct uses here.
         if (!isa<AllocaInst>(V))