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.

llvm-svn: 200093

1 files changed, 11 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
index 93ee38bc0bf..f0de7982b12 100644
--- a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -45,6 +45,15 @@ static cl::opt<bool> EnableAASchedMI("enable-aa-sched-mi", cl::Hidden,
     cl::ZeroOrMore, cl::init(false),
     cl::desc("Enable use of AA during MI GAD construction"));
 
+// FIXME: Enable the use of TBAA. There are two known issues preventing this:
+//   1. Stack coloring does not update TBAA when merging allocas
+//   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.
+static cl::opt<bool> UseTBAA("use-tbaa-in-sched-mi", cl::Hidden,
+    cl::init(false), cl::desc("Enable use of TBAA during MI GAD construction"));
+
 ScheduleDAGInstrs::ScheduleDAGInstrs(MachineFunction &mf,
                                      const MachineLoopInfo &mli,
                                      const MachineDominatorTree &mdt,
@@ -556,9 +565,9 @@ static bool MIsNeedChainEdge(AliasAnalysis *AA, const MachineFrameInfo *MFI,
 
   AliasAnalysis::AliasResult AAResult = AA->alias(
   AliasAnalysis::Location(MMOa->getValue(), Overlapa,
-                          MMOa->getTBAAInfo()),
+                          UseTBAA ? MMOa->getTBAAInfo() : 0),
   AliasAnalysis::Location(MMOb->getValue(), Overlapb,
-                          MMOb->getTBAAInfo()));
+                          UseTBAA ? MMOb->getTBAAInfo() : 0));
 
   return (AAResult != AliasAnalysis::NoAlias);
 }