[clang] Frontend: Destroy compiling compiler instance before read

[AnthonyLatsis]

Upstreams swiftlang#10943.

#134887 added a clone for the compiler instance in compileModuleAndReadASTImpl, which would then be destroyed after the corresponding read in the importing instance.

Swift has a SwiftNameLookupExtension module extension which updates (effectively) global state - populating the lookup table for a module on read and removing it when the module is destroyed.

With newly cloned instance, we would then see:

• Module compiled with cloned instance
• Module read with importing instance
• Lookup table for that module added
• Cloned instance destroyed
• Module from that cloned instance destroyed
• Lookup table for that module name removed

Depending on the original semantics is incredibly fragile, but for now it's good enough to ensure that the read in the importing instance is after the cloned instanced is destroyed. Ideally we'd only ever add to the lookup tables in the original importing instance, never its clones.

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[llvmbot]

@llvm/pr-subscribers-clang

Author: Anthony Latsis (AnthonyLatsis)

Changes

Upstreams swiftlang#10943.

#134887 added a clone for the compiler instance in compileModuleAndReadASTImpl, which would then be destroyed after the corresponding read in the importing instance.

Swift has a SwiftNameLookupExtension module extension which updates (effectively) global state - populating the lookup table for a module on read and removing it when the module is destroyed.

With newly cloned instance, we would then see:

• Module compiled with cloned instance
• Module read with importing instance
• Lookup table for that module added
• Cloned instance destroyed
• Module from that cloned instance destroyed
• Lookup table for that module name removed

Depending on the original semantics is incredibly fragile, but for now it's good enough to ensure that the read in the importing instance is after the cloned instanced is destroyed. Ideally we'd only ever add to the lookup tables in the original importing instance, never its clones.

---

Full diff: https://github.com/llvm/llvm-project/pull/154455.diff

1 Files Affected:

• (modified) clang/lib/Frontend/CompilerInstance.cpp (+12-10)

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 9f99edadbb70f..28f65b7f8912f 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1473,16 +1473,18 @@ static bool compileModuleAndReadASTImpl(CompilerInstance &ImportingInstance,
                                         SourceLocation ModuleNameLoc,
                                         Module *Module,
                                         StringRef ModuleFileName) {
-  auto Instance = ImportingInstance.cloneForModuleCompile(ModuleNameLoc, Module,
-                                                          ModuleFileName);
-
-  if (!ImportingInstance.compileModule(ModuleNameLoc,
-                                       Module->getTopLevelModuleName(),
-                                       ModuleFileName, *Instance)) {
-    ImportingInstance.getDiagnostics().Report(ModuleNameLoc,
-                                              diag::err_module_not_built)
-        << Module->Name << SourceRange(ImportLoc, ModuleNameLoc);
-    return false;
+  {
+    auto Instance = ImportingInstance.cloneForModuleCompile(ModuleNameLoc, Module,
+                                                            ModuleFileName);
+
+    if (!ImportingInstance.compileModule(ModuleNameLoc,
+                                         Module->getTopLevelModuleName(),
+                                         ModuleFileName, *Instance)) {
+      ImportingInstance.getDiagnostics().Report(ModuleNameLoc,
+                                                diag::err_module_not_built)
+          << Module->Name << SourceRange(ImportLoc, ModuleNameLoc);
+      return false;
+    }
   }
 
   // The module is built successfully, we can update its timestamp now.