Stop producing line and file debug information for clang::Decls.

It would be nice to query the clang::SourceManager for the source
location of the clang::Decl in IRGenDebugInfo, but module out-of-date
rebuilds may unload previously loaded clang::Modules and thus also
invalidate source locations pointed to, leading to a use-after-free
here. If this functionality is desired, the source location must be
captured by ClangImporter and stored on the side.

LLDB does not actually make use of this information for non-C++ types
(it is really helpful with debugging the debug info itself, though),
so we can avoid the potential use-after-free and crash by not doing it.

<rdar://problem/48509051>

Author: adrian-prantl

lib/IRGen/IRGenDebugInfo.cpp

@@ -240,14 +240,14 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
     if (!D)
       return L;
 
-    if (auto *ClangDecl = D->getClangDecl()) {
-      auto ClangSrcLoc = ClangDecl->getBeginLoc();
-      clang::SourceManager &ClangSM =
-          CI.getClangASTContext().getSourceManager();
-      L.Line = ClangSM.getPresumedLineNumber(ClangSrcLoc);
-      L.Filename = ClangSM.getBufferName(ClangSrcLoc);
-      return L;
-    }
+    // If D is a clang::Decl, it would be nice to query the clang::SourceManager
+    // for the source location of the clang::Decl here, but module out-of-date
+    // rebuilds may unload previously loaded clang::Modules and thus also
+    // invalidate source locations pointed to, leading to a use-after-free
+    // here. If this functionality is desired, the source location must be
+    // captured by ClangImporter and stored on the side.
+    // LLDB only uses the DW_AT_decl_file / DW_AT_decl_line for C++ types.
+
     return getSwiftDebugLoc(DI, D, End);
   }
 

test/ClangImporter/objc_ir.swift

@@ -360,10 +360,11 @@ func testBlocksWithGenerics(hba: HasBlockArray) -> Any {
 // CHECK: attributes [[NOUNWIND]] = { nounwind }
 
 // CHECK: ![[SWIFT_NAME_ALIAS_VAR]] = !DILocalVariable(name: "obj", arg: 1, scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: ![[SWIFT_NAME_ALIAS_TYPE:[0-9]+]])
-// CHECK: ![[SWIFT_NAME_ALIAS_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$sSo14SwiftNameAliasaD", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, baseType: !{{[0-9]+}})
+// CHECK: ![[SWIFT_NAME_ALIAS_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$sSo14SwiftNameAliasaD", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, baseType: !{{[0-9]+}})
 
 // CHECK: ![[SWIFT_GENERIC_NAME_ALIAS_VAR]] = !DILocalVariable(name: "generic_obj", arg: 1, scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: ![[SWIFT_GENERIC_NAME_ALIAS_TYPE:[0-9]+]])
-// CHECK: ![[SWIFT_GENERIC_NAME_ALIAS_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$sSo21SwiftGenericNameAliasaySo8NSNumberCGD", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, baseType: !{{[0-9]+}})
+// CHECK: ![[SWIFT_GENERIC_NAME_ALIAS_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$sSo21SwiftGenericNameAliasaySo8NSNumberCGD", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, baseType: !{{[0-9]+}})
 
 // CHECK: ![[SWIFT_CONSTR_GENERIC_NAME_ALIAS_VAR]] = !DILocalVariable(name: "constr_generic_obj", arg: 1, scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, type: ![[SWIFT_CONSTR_GENERIC_NAME_ALIAS_TYPE:[0-9]+]])
-// CHECK: ![[SWIFT_CONSTR_GENERIC_NAME_ALIAS_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$sSo27SwiftConstrGenericNameAliasaySo8NSNumberCGD", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, line: {{[0-9]+}}, baseType: !{{[0-9]+}})
+// CHECK: ![[SWIFT_CONSTR_GENERIC_NAME_ALIAS_TYPE]] = !DIDerivedType(tag: DW_TAG_typedef, name: "$sSo27SwiftConstrGenericNameAliasaySo8NSNumberCGD", scope: !{{[0-9]+}}, file: !{{[0-9]+}}, baseType: !{{[0-9]+}})
+