[clang] [clang][CodeGen] Add reloadLinkModules to reload link modules for incremental compilation (PR #229741)

[Aditya Sinha via cfe-commits]

https://github.com/AdityaSinha149 created https://github.com/llvm/llvm-project/pull/229741

This PR adds an option to reload `LinkModules`. In incremental mode (clang-repl), multiple TUs use the same `BackendConsumer`, but `LinkModules` are consumed after the first TU is processed, so they need to be reloaded for every TU. It is not called yet; a follow-up for HIP support in clang-repl will use it.

This PR also adds a test that checks a library is linked into a first TU, not into a second, and linked again after the reload.

>From 56f30a4141bf86d40822b5fa0797a6a59c20b9dc Mon Sep 17 00:00:00 2001
From: AdityaSinha149 <adsinha at amd.com>
Date: Wed, 7 Oct 2026 17:19:51 +0530
Subject: [PATCH] [clang][CodeGen] Add reloadLinkModules to reload link modules
 for incremental compilation

---
 clang/include/clang/CodeGen/CodeGenAction.h | 3 +++
 clang/lib/CodeGen/BackendConsumer.h         | 8 ++++++++
 clang/lib/CodeGen/CodeGenAction.cpp         | 9 +++++++++
 3 files changed, 20 insertions(+)

diff --git a/clang/include/clang/CodeGen/CodeGenAction.h b/clang/include/clang/CodeGen/CodeGenAction.h
index 84fa4549d5033..e7d89306154d1 100644
--- a/clang/include/clang/CodeGen/CodeGenAction.h
+++ b/clang/include/clang/CodeGen/CodeGenAction.h
@@ -63,6 +63,9 @@ class CodeGenAction : public ASTFrontendAction {
 
   CodeGenerator *getCodeGenerator() const;
 
+  /// Reload the -mlink-builtin-bitcode modules into the backend consumer.
+  void reloadLinkModules(CompilerInstance &CI);
+
   BackendConsumer *BEConsumer = nullptr;
 };
 
diff --git a/clang/lib/CodeGen/BackendConsumer.h b/clang/lib/CodeGen/BackendConsumer.h
index 5337a5f7a1b4a..490be03bf14f7 100644
--- a/clang/lib/CodeGen/BackendConsumer.h
+++ b/clang/lib/CodeGen/BackendConsumer.h
@@ -76,6 +76,14 @@ class BackendConsumer : public ASTConsumer {
 
   // Links each entry in LinkModules into our module.  Returns true on error.
   bool LinkInModules(llvm::Module *M);
+
+  /// Reloads a set of modules to link in. LinkInModules() consume the modules,
+  /// so incremental compilation(clang-repl) needs to reload the modules for
+  /// every TU.
+  void setLinkModules(SmallVector<LinkModule, 4> LMs) {
+    LinkModules = std::move(LMs);
+  }
+
   /// Create an llvm::DiagnosticHandler that routes LLVM backend diagnostics
   /// through this consumer's clang diagnostics.
   std::unique_ptr<llvm::DiagnosticHandler> createDiagnosticHandler();
diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
index 1abd8b0455a19..0511ddf596247 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -365,6 +365,15 @@ CodeGenerator *CodeGenAction::getCodeGenerator() const {
   return BEConsumer->getCodeGenerator();
 }
 
+void CodeGenAction::reloadLinkModules(CompilerInstance &CI) {
+  if (!BEConsumer)
+    return;
+  SmallVector<LinkModule, 4> LMs;
+  if (clang::loadLinkModules(CI, *VMContext, LMs))
+    return;
+  BEConsumer->setLinkModules(std::move(LMs));
+}
+
 bool CodeGenAction::BeginSourceFileAction(CompilerInstance &CI) {
   if (CI.getFrontendOpts().GenReducedBMI)
     CI.getLangOpts().setCompilingModule(LangOptions::CMK_ModuleInterface);