Improve merging of debug locations (fixes PR 36410)

Patch by Ulrich Weigand!

Pulling this in ahead of time to unblock a crash in the swift compiler.

rdar://problem/38225089

Author: adrian-prantl

lib/IR/DebugInfoMetadata.cpp

@@ -80,17 +80,47 @@ DILocation::getMergedLocation(const DILocation *LocA, const DILocation *LocB,
   if (!dyn_cast_or_null<CallInst>(ForInst))
     return nullptr;
 
+  // Find closest common scope for LocA and LocB.
+  DIScope *CommonScope = nullptr;
+  SmallPtrSet<DIScope *, 5> ScopesA;
+  for (DIScope *S = LocA->getScope(); S; S = S->getScope().resolve())
+    ScopesA.insert(S);
+  for (DIScope *S = LocB->getScope(); S; S = S->getScope().resolve())
+    if (ScopesA.count(S)) {
+      CommonScope = S;
+      break;
+    }
+
+  // If no common scope exists, make up a new compiler-generated location.
+  // At this point the inlinedAt field will be meaningless as well.
+  if (!CommonScope)
+    return DILocation::get(LocA->getContext(),
+                           0, 0, LocA->getInlinedAtScope());
+
+  // If either LocA or LocB is not inlined, the merged location does not
+  // need to be inlined either.
+  if (LocA->getInlinedAt() == nullptr || LocB->getInlinedAt() == nullptr)
+    return DILocation::get(LocA->getContext(), 0, 0, CommonScope);
+
+  // Otherwise find the closest common inlined-at location for LocA and LocB.
+  DILocation *CommonInlinedAt = nullptr;
   SmallPtrSet<DILocation *, 5> InlinedLocationsA;
   for (DILocation *L = LocA->getInlinedAt(); L; L = L->getInlinedAt())
     InlinedLocationsA.insert(L);
-  const DILocation *Result = LocB;
-  for (DILocation *L = LocB->getInlinedAt(); L; L = L->getInlinedAt()) {
-    Result = L;
-    if (InlinedLocationsA.count(L))
+  for (DILocation *L = LocB->getInlinedAt(); L; L = L->getInlinedAt())
+    if (InlinedLocationsA.count(L)) {
+      CommonInlinedAt = L;
       break;
-  }
-  return DILocation::get(Result->getContext(), 0, 0, Result->getScope(),
-                         Result->getInlinedAt());
+    }
+
+  // If no common inlined-at location exists, mark as inlined at a
+  // compiler-generated location in the current function.
+  if (!CommonInlinedAt)
+    CommonInlinedAt = DILocation::get(LocA->getContext(),
+                                      0, 0, LocA->getInlinedAtScope());
+
+  return DILocation::get(LocA->getContext(),
+                         0, 0, CommonScope, CommonInlinedAt);
 }
 
 DINode::DIFlags DINode::getFlag(StringRef Flag) {

unittests/IR/MetadataTest.cpp

@@ -883,6 +883,81 @@ TEST_F(DILocationTest, cloneTemporary) {
   EXPECT_TRUE(L2->isTemporary());
 }
 
+TEST_F(DILocationTest, getMergedLocation) {
+  FunctionType *FT = FunctionType::get(Type::getVoidTy(Context), false);
+  auto *F = Function::Create(FT, GlobalValue::ExternalLinkage);
+  const CallInst *Call = CallInst::Create(F, None);
+
+  // Merging two identical locations should result in the same location.
+  {
+    DISubprogram *Prg = getSubprogram();
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg);
+    DILocation *L2 = DILocation::get(Context, 2, 7, Prg);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, nullptr);
+    EXPECT_EQ(2u, L->getLine());
+    EXPECT_EQ(7u, L->getColumn());
+    EXPECT_EQ(Prg, L->getScope());
+  }
+  // If the two locations are incompatible, there should be a null result.
+  {
+    DISubprogram *Prg = getSubprogram();
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg);
+    DILocation *L2 = DILocation::get(Context, 3, 7, Prg);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, nullptr);
+    EXPECT_EQ(nullptr, L);
+  }
+  // Unless we are merging locations for a call instruction.  If the
+  // scopes agree, the result should be a compiler-generated location
+  // in that same scope.
+  {
+    DISubprogram *Prg = getSubprogram();
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg);
+    DILocation *L2 = DILocation::get(Context, 3, 7, Prg);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, Call);
+    EXPECT_EQ(0u, L->getLine());
+    EXPECT_EQ(Prg, L->getScope());
+  }
+  // Likewise if the one scope is a sub-scope of the other.
+  {
+    DISubprogram *Prg = getSubprogram();
+    DILexicalBlock *B = DILexicalBlock::get(Context, Prg, getFile(), 5, 7);
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg);
+    DILocation *L2 = DILocation::get(Context, 3, 7, B);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, Call);
+    EXPECT_EQ(0u, L->getLine());
+    EXPECT_EQ(Prg, L->getScope());
+  }
+  // Even if the calls were inlined (possibly into different places),
+  // if they originate from the same scope, the result should also be
+  // a compiler-generated location in that same scope.
+  {
+    DISubprogram *IPrg = getSubprogram();
+    DILocation *I1 = DILocation::get(Context, 10, 7, IPrg);
+    DILocation *I2 = DILocation::get(Context, 11, 7, IPrg);
+    DISubprogram *Prg = getSubprogram();
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg, I1);
+    DILocation *L2 = DILocation::get(Context, 3, 7, Prg, I2);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, Call);
+    EXPECT_EQ(0u, L->getLine());
+    EXPECT_EQ(Prg, L->getScope());
+    EXPECT_NE(nullptr, L->getInlinedAt());
+  }
+  // Likewise if the one scope is a sub-scope of the other.
+  {
+    DISubprogram *IPrg = getSubprogram();
+    DILocation *I1 = DILocation::get(Context, 10, 7, IPrg);
+    DILocation *I2 = DILocation::get(Context, 11, 7, IPrg);
+    DISubprogram *Prg = getSubprogram();
+    DILexicalBlock *B = DILexicalBlock::get(Context, Prg, getFile(), 5, 7);
+    DILocation *L1 = DILocation::get(Context, 2, 7, Prg, I1);
+    DILocation *L2 = DILocation::get(Context, 3, 7, B, I2);
+    const DILocation *L = DILocation::getMergedLocation(L1, L2, Call);
+    EXPECT_EQ(0u, L->getLine());
+    EXPECT_EQ(Prg, L->getScope());
+    EXPECT_NE(nullptr, L->getInlinedAt());
+  }
+}
+
 typedef MetadataTest GenericDINodeTest;
 
 TEST_F(GenericDINodeTest, get) {