Correctly combine alias.scope metadata by a union instead of intersecting

Summary:
The alias.scope metadata represents sets of things an instruction might
alias with. When generically combining the metadata from two
instructions the result must be the union of the original sets, because
the new instruction might alias with anything any of the original
instructions aliased with.

Reviewers: hfinkel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D7490

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228525 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/Metadata.h

@@ -879,6 +879,7 @@ public:
   static MDNode *getMostGenericTBAA(MDNode *A, MDNode *B);
   static MDNode *getMostGenericFPMath(MDNode *A, MDNode *B);
   static MDNode *getMostGenericRange(MDNode *A, MDNode *B);
+  static MDNode *getMostGenericAliasScope(MDNode *A, MDNode *B);
 };
 
 /// \brief Tuple of metadata.

lib/Analysis/TypeBasedAliasAnalysis.cpp

@@ -623,8 +623,8 @@ void Instruction::getAAMetadata(AAMDNodes &N, bool Merge) const {
     N.TBAA = getMetadata(LLVMContext::MD_tbaa);
 
   if (Merge)
-    N.Scope =
+    N.Scope = MDNode::getMostGenericAliasScope(
-        MDNode::intersect(N.Scope, getMetadata(LLVMContext::MD_alias_scope));
+        N.Scope, getMetadata(LLVMContext::MD_alias_scope));
   else
     N.Scope = getMetadata(LLVMContext::MD_alias_scope);
 

lib/IR/Metadata.cpp

@@ -782,6 +782,28 @@ MDNode *MDNode::intersect(MDNode *A, MDNode *B) {
   return getOrSelfReference(A->getContext(), MDs);
 }
 
+MDNode *MDNode::getMostGenericAliasScope(MDNode *A, MDNode *B) {
+  if (!A || !B)
+    return nullptr;
+
+  SmallVector<Metadata *, 4> MDs(B->op_begin(), B->op_end());
+  for (unsigned i = 0, ie = A->getNumOperands(); i != ie; ++i) {
+    Metadata *MD = A->getOperand(i);
+    bool insert = true;
+    for (unsigned j = 0, je = B->getNumOperands(); j != je; ++j)
+      if (MD == B->getOperand(j)) {
+        insert = false;
+        break;
+      }
+    if (insert)
+        MDs.push_back(MD);
+  }
+
+  // FIXME: This preserves long-standing behaviour, but is it really the right
+  // behaviour?  Or was that an unintended side-effect of node uniquing?
+  return getOrSelfReference(A->getContext(), MDs);
+}
+
 MDNode *MDNode::getMostGenericFPMath(MDNode *A, MDNode *B) {
   if (!A || !B)
     return nullptr;

lib/Transforms/Utils/Local.cpp

@@ -1334,6 +1334,8 @@ void llvm::combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsign
         K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
         break;
       case LLVMContext::MD_alias_scope:
+        K->setMetadata(Kind, MDNode::getMostGenericAliasScope(JMD, KMD));
+        break;
       case LLVMContext::MD_noalias:
         K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
         break;

lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -217,6 +217,8 @@ static Instruction *propagateMetadata(Instruction *I, ArrayRef<Value *> VL) {
         MD = MDNode::getMostGenericTBAA(MD, IMD);
         break;
       case LLVMContext::MD_alias_scope:
+        MD = MDNode::getMostGenericAliasScope(MD, IMD);
+        break;
       case LLVMContext::MD_noalias:
         MD = MDNode::intersect(MD, IMD);
         break;

test/Transforms/Util/combine-alias-scope-metadata.ll

@@ -0,0 +1,24 @@
+; RUN: opt < %s -S -basicaa -memcpyopt | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @test(i8* noalias dereferenceable(1) %in, i8* noalias dereferenceable(1) %out) {
+  %tmp = alloca i8
+  %tmp2 = alloca i8
+; CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* %out, i8* %in, i64 1, i32 8, i1 false)
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %tmp, i8* %in, i64 1, i32 8, i1 false), !alias.scope !4
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %tmp2, i8* %tmp, i64 1, i32 8, i1 false), !alias.scope !5
+
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* %out, i8* %tmp2, i64 1, i32 8, i1 false), !noalias !6
+
+  ret void
+}
+
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8*, i8*, i64, i32, i1)
+
+!0 = !{!0}
+!1 = distinct !{!1, !0, !"in"}
+!2 = distinct !{!2, !0, !"tmp"}
+!3 = distinct !{!3, !0, !"tmp2"}
+!4 = distinct !{!1, !2}
+!5 = distinct !{!2, !3}
+!6 = distinct !{!1, !2}