[TBAA] Drop support for "old style" scalar TBAA tags

Summary:
We've had support for auto upgrading old style scalar TBAA access
metadata tags into the "new" struct path aware TBAA metadata for 3 years
now.  The only way to actually generate old style TBAA was explicitly
through the IRBuilder API.  I think this is a good time for dropping
support for old style scalar TBAA.

I'm not removing support for textual or bitcode upgrade -- if you have
IR with the old style scalar TBAA tags that go through the AsmParser orf
the bitcode parser before LLVM sees them, they will keep working as
usual.

Note:

  %val = load i32, i32* %ptr, !tbaa !N
  !N = < scalar tbaa node >

is equivalent to

  %val = load i32, i32* %ptr, !tbaa !M
  !N = < scalar tbaa node >
  !M = !{!N, !N, 0}

Reviewers: manmanren, chandlerc, sunfish

Subscribers: mcrosier, llvm-commits, mgorny

Differential Revision: https://reviews.llvm.org/D26229

llvm-svn: 286291

2 files changed, 23 insertions, 57 deletions

diff --git a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
index 1baa095a243..e5ef734aab5 100644
--- a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
@@ -417,15 +417,14 @@ MDNode *MDNode::getMostGenericTBAA(MDNode *A, MDNode *B) {
     return A;
 
   // For struct-path aware TBAA, we use the access type of the tag.
-  bool StructPath = isStructPathTBAA(A) && isStructPathTBAA(B);
-  if (StructPath) {
-    A = cast_or_null<MDNode>(MutableTBAAStructTagNode(A).getAccessType());
-    if (!A)
-      return nullptr;
-    B = cast_or_null<MDNode>(MutableTBAAStructTagNode(B).getAccessType());
-    if (!B)
-      return nullptr;
-  }
+  assert(isStructPathTBAA(A) && isStructPathTBAA(B) &&
+         "Auto upgrade should have taken care of this!");
+  A = cast_or_null<MDNode>(MutableTBAAStructTagNode(A).getAccessType());
+  if (!A)
+    return nullptr;
+  B = cast_or_null<MDNode>(MutableTBAAStructTagNode(B).getAccessType());
+  if (!B)
+    return nullptr;
 
   SmallSetVector<MDNode *, 4> PathA;
   MutableTBAANode TA(A);
@@ -457,8 +456,6 @@ MDNode *MDNode::getMostGenericTBAA(MDNode *A, MDNode *B) {
     --IA;
     --IB;
   }
-  if (!StructPath)
-    return Ret;
 
   if (!Ret)
     return nullptr;
@@ -492,52 +489,8 @@ void Instruction::getAAMetadata(AAMDNodes &N, bool Merge) const {
 /// Aliases - Test whether the type represented by A may alias the
 /// type represented by B.
 bool TypeBasedAAResult::Aliases(const MDNode *A, const MDNode *B) const {
-  // Make sure that both MDNodes are struct-path aware.
-  if (isStructPathTBAA(A) && isStructPathTBAA(B))
-    return PathAliases(A, B);
-
-  // Keep track of the root node for A and B.
-  TBAANode RootA, RootB;
-
-  // Climb the tree from A to see if we reach B.
-  for (TBAANode T(A);;) {
-    if (T.getNode() == B)
-      // B is an ancestor of A.
-      return true;
-
-    RootA = T;
-    T = T.getParent();
-    if (!T.getNode())
-      break;
-  }
-
-  // Climb the tree from B to see if we reach A.
-  for (TBAANode T(B);;) {
-    if (T.getNode() == A)
-      // A is an ancestor of B.
-      return true;
-
-    RootB = T;
-    T = T.getParent();
-    if (!T.getNode())
-      break;
-  }
-
-  // Neither node is an ancestor of the other.
-
-  // If they have different roots, they're part of different potentially
-  // unrelated type systems, so we must be conservative.
-  if (RootA.getNode() != RootB.getNode())
-    return true;
-
-  // If they have the same root, then we've proved there's no alias.
-  return false;
-}
-
-/// Test whether the struct-path tag represented by A may alias the
-/// struct-path tag represented by B.
-bool TypeBasedAAResult::PathAliases(const MDNode *A, const MDNode *B) const {
-  // Verify that both input nodes are struct-path aware.
+  // Verify that both input nodes are struct-path aware.  Auto-upgrade should
+  // have taken care of this.
   assert(isStructPathTBAA(A) && "MDNode A is not struct-path aware.");
   assert(isStructPathTBAA(B) && "MDNode B is not struct-path aware.");
 
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index a8a1df3e8b4..31a181e8db4 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -391,6 +391,7 @@ private:
   void visitBasicBlock(BasicBlock &BB);
   void visitRangeMetadata(Instruction& I, MDNode* Range, Type* Ty);
   void visitDereferenceableMetadata(Instruction& I, MDNode* MD);
+  void visitTBAAMetadata(Instruction &I, MDNode *MD);
 
   template <class Ty> bool isValidMetadataArray(const MDTuple &N);
 #define HANDLE_SPECIALIZED_MDNODE_LEAF(CLASS) void visit##CLASS(const CLASS &N);
@@ -3658,6 +3659,15 @@ void Verifier::visitDereferenceableMetadata(Instruction& I, MDNode* MD) {
          "dereferenceable_or_null metadata value must be an i64!", &I);
 }
 
+void Verifier::visitTBAAMetadata(Instruction &I, MDNode *MD) {
+  bool IsStructPathTBAA =
+      isa<MDNode>(MD->getOperand(0)) && MD->getNumOperands() >= 3;
+
+  Assert(IsStructPathTBAA,
+         "Old-style TBAA is no longer allowed, use struct-path TBAA instead",
+         &I);
+}
+
 /// verifyInstruction - Verify that an instruction is well formed.
 ///
 void Verifier::visitInstruction(Instruction &I) {
@@ -3793,6 +3803,9 @@ void Verifier::visitInstruction(Instruction &I) {
   if (MDNode *MD = I.getMetadata(LLVMContext::MD_dereferenceable_or_null))
     visitDereferenceableMetadata(I, MD);
 
+  if (MDNode *MD = I.getMetadata(LLVMContext::MD_tbaa))
+    visitTBAAMetadata(I, MD);
+
   if (MDNode *AlignMD = I.getMetadata(LLVMContext::MD_align)) {
     Assert(I.getType()->isPointerTy(), "align applies only to pointer types",
            &I);