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
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index af7519a..b95a6c1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -56,6 +56,16 @@
CombinerGlobalAA("combiner-global-alias-analysis", cl::Hidden,
cl::desc("Enable DAG combiner's use of IR alias analysis"));
+// 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("combiner-use-tbaa", cl::Hidden, cl::init(false),
+ cl::desc("Enable DAG combiner's use of TBAA"));
+
#ifndef NDEBUG
static cl::opt<std::string>
CombinerAAOnlyFunc("combiner-aa-only-func", cl::Hidden,
@@ -11079,8 +11089,10 @@
int64_t Overlap1 = Size1 + SrcValueOffset1 - MinOffset;
int64_t Overlap2 = Size2 + SrcValueOffset2 - MinOffset;
AliasAnalysis::AliasResult AAResult =
- AA.alias(AliasAnalysis::Location(SrcValue1, Overlap1, TBAAInfo1),
- AliasAnalysis::Location(SrcValue2, Overlap2, TBAAInfo2));
+ AA.alias(AliasAnalysis::Location(SrcValue1, Overlap1,
+ UseTBAA ? TBAAInfo1 : 0),
+ AliasAnalysis::Location(SrcValue2, Overlap2,
+ UseTBAA ? TBAAInfo2 : 0));
if (AAResult == AliasAnalysis::NoAlias)
return false;
}