Prevent DILocation::getMergedLocation() from creating invalid metadata.

The function's new implementation from r340583 had a bug in it that
could cause an invalid scope to be generated when merging two
DILocations with no common ancestor scope.

This patch detects this situation and picks the scope of the first
location. This is not perfect, because the scope is misleading, but on
the other hand, this will be a line 0 location.

rdar://problem/43687474

Differential Revision: https://reviews.llvm.org/D51238

llvm-svn: 340672

2 files changed, 83 insertions, 0 deletions

diff --git a/llvm/lib/IR/DebugInfoMetadata.cpp b/llvm/lib/IR/DebugInfoMetadata.cpp
index 0ceded07679..7a6160244ec 100644
--- a/llvm/lib/IR/DebugInfoMetadata.cpp
+++ b/llvm/lib/IR/DebugInfoMetadata.cpp
@@ -102,6 +102,11 @@ const DILocation *DILocation::getMergedLocation(const DILocation *LocA,
       L = L->getInlinedAt();
     }
   }
+
+  // If the two locations are irreconsilable, just pick one. This is misleading,
+  // but on the other hand, it's a "line 0" location.
+  if (!S || !isa<DILocalScope>(S))
+    S = LocA->getScope();
   return DILocation::get(Result->getContext(), 0, 0, S, L);
 }
 
diff --git a/llvm/unittests/IR/MetadataTest.cpp b/llvm/unittests/IR/MetadataTest.cpp
index 9bb54c4deb0..48c6cfa9ac8 100644
--- a/llvm/unittests/IR/MetadataTest.cpp
+++ b/llvm/unittests/IR/MetadataTest.cpp
@@ -860,6 +860,84 @@ TEST_F(DILocationTest, Overflow) {
   }
 }
 
+TEST_F(DILocationTest, Merge) {
+  DISubprogram *N = getSubprogram();
+  DIScope *S = DILexicalBlock::get(Context, N, getFile(), 3, 4);
+
+  {
+    // Identical.
+    auto *A = DILocation::get(Context, 2, 7, N);
+    auto *B = DILocation::get(Context, 2, 7, N);
+    auto *M = DILocation::getMergedLocation(A, B);
+    EXPECT_EQ(2u, M->getLine());
+    EXPECT_EQ(7u, M->getColumn());
+    EXPECT_EQ(N, M->getScope());
+  }
+
+  {
+    // Identical, different scopes.
+    auto *A = DILocation::get(Context, 2, 7, N);
+    auto *B = DILocation::get(Context, 2, 7, S);
+    auto *M = DILocation::getMergedLocation(A, B);
+    EXPECT_EQ(0u, M->getLine()); // FIXME: Should this be 2?
+    EXPECT_EQ(0u, M->getColumn()); // FIXME: Should this be 7?
+    EXPECT_EQ(N, M->getScope());
+  }
+
+  {
+    // Different lines, same scopes.
+    auto *A = DILocation::get(Context, 1, 6, N);
+    auto *B = DILocation::get(Context, 2, 7, N);
+    auto *M = DILocation::getMergedLocation(A, B);
+    EXPECT_EQ(0u, M->getLine());
+    EXPECT_EQ(0u, M->getColumn());
+    EXPECT_EQ(N, M->getScope());
+  }
+
+  {
+    // Twisty locations, all different, same function.
+    auto *A = DILocation::get(Context, 1, 6, N);
+    auto *B = DILocation::get(Context, 2, 7, S);
+    auto *M = DILocation::getMergedLocation(A, B);
+    EXPECT_EQ(0u, M->getLine());
+    EXPECT_EQ(0u, M->getColumn());
+    EXPECT_EQ(N, M->getScope());
+  }
+
+  {
+    // Different function, same inlined-at.
+    auto *F = getFile();
+    auto *SP1 = DISubprogram::getDistinct(Context, F, "a", "a", F, 0, nullptr,
+                                          false, false, 0, nullptr, 0, 0, 0,
+                                          DINode::FlagZero, false, nullptr);
+    auto *SP2 = DISubprogram::getDistinct(Context, F, "b", "b", F, 0, nullptr,
+                                          false, false, 0, nullptr, 0, 0, 0,
+                                          DINode::FlagZero, false, nullptr);
+
+    auto *I = DILocation::get(Context, 2, 7, N);
+    auto *A = DILocation::get(Context, 1, 6, SP1, I);
+    auto *B = DILocation::get(Context, 2, 7, SP2, I);
+    auto *M = DILocation::getMergedLocation(A, B);
+    EXPECT_EQ(0u, M->getLine());
+    EXPECT_EQ(0u, M->getColumn());
+    EXPECT_TRUE(isa<DILocalScope>(M->getScope()));
+    EXPECT_EQ(I, M->getInlinedAt());
+  }
+
+   {
+    // Completely different.
+    auto *I = DILocation::get(Context, 2, 7, N);
+    auto *A = DILocation::get(Context, 1, 6, S, I);
+    auto *B = DILocation::get(Context, 2, 7, getSubprogram());
+    auto *M = DILocation::getMergedLocation(A, B);
+    EXPECT_EQ(0u, M->getLine());
+    EXPECT_EQ(0u, M->getColumn());
+    EXPECT_TRUE(isa<DILocalScope>(M->getScope()));
+    EXPECT_EQ(S, M->getScope());
+    EXPECT_EQ(nullptr, M->getInlinedAt());
+  }
+}
+
 TEST_F(DILocationTest, getDistinct) {
   MDNode *N = getSubprogram();
   DILocation *L0 = DILocation::getDistinct(Context, 2, 7, N);