[clang][fat-lto-objects] Make module flags match non-FatLTO pipelines (#83159)

In addition to being rather hard to follow, there isn't a good reason
why FatLTO shouldn't just share the same code for setting module flags
for (Thin)LTO. This patch simplifies the logic and makes sure we use set
these flags in a consistent way, independent of FatLTO.

Additionally, we now test that output in the .llvm.lto section actually
matches the output from Full and Thin LTO compilation.

1 files changed, 16 insertions, 16 deletions

diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index a310825..056f790 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -186,6 +186,14 @@ class EmitAssemblyHelper {
            TargetTriple.getVendor() != llvm::Triple::Apple;
   }
 
+  /// Check whether we should emit a flag for UnifiedLTO.
+  /// The UnifiedLTO module flag should be set when UnifiedLTO is enabled for
+  /// ThinLTO or Full LTO with module summaries.
+  bool shouldEmitUnifiedLTOModueFlag() const {
+    return CodeGenOpts.UnifiedLTO &&
+           (CodeGenOpts.PrepareForThinLTO || shouldEmitRegularLTOSummary());
+  }
+
 public:
   EmitAssemblyHelper(DiagnosticsEngine &_Diags,
                      const HeaderSearchOptions &HeaderSearchOpts,
@@ -1036,7 +1044,8 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
   if (!actionRequiresCodeGen(Action) && CodeGenOpts.VerifyModule)
     MPM.addPass(VerifierPass());
 
-  if (Action == Backend_EmitBC || Action == Backend_EmitLL) {
+  if (Action == Backend_EmitBC || Action == Backend_EmitLL ||
+      CodeGenOpts.FatLTO) {
     if (CodeGenOpts.PrepareForThinLTO && !CodeGenOpts.DisableLLVMPasses) {
       if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
         TheModule->addModuleFlag(llvm::Module::Error, "EnableSplitLTOUnit",
@@ -1047,11 +1056,9 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
           if (!ThinLinkOS)
             return;
         }
-        if (CodeGenOpts.UnifiedLTO)
-          TheModule->addModuleFlag(llvm::Module::Error, "UnifiedLTO", uint32_t(1));
         MPM.addPass(ThinLTOBitcodeWriterPass(
             *OS, ThinLinkOS ? &ThinLinkOS->os() : nullptr));
-      } else {
+      } else if (Action == Backend_EmitLL) {
         MPM.addPass(PrintModulePass(*OS, "", CodeGenOpts.EmitLLVMUseLists,
                                     /*EmitLTOSummary=*/true));
       }
@@ -1065,24 +1072,17 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
         if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
           TheModule->addModuleFlag(llvm::Module::Error, "EnableSplitLTOUnit",
                                    uint32_t(1));
-        if (CodeGenOpts.UnifiedLTO)
-          TheModule->addModuleFlag(llvm::Module::Error, "UnifiedLTO", uint32_t(1));
       }
-      if (Action == Backend_EmitBC)
+      if (Action == Backend_EmitBC) {
         MPM.addPass(BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists,
                                       EmitLTOSummary));
-      else
+      } else if (Action == Backend_EmitLL) {
         MPM.addPass(PrintModulePass(*OS, "", CodeGenOpts.EmitLLVMUseLists,
                                     EmitLTOSummary));
+      }
     }
-  }
-  if (CodeGenOpts.FatLTO) {
-    // Set the EnableSplitLTOUnit and UnifiedLTO module flags, since FatLTO
-    // uses a different action than Backend_EmitBC or Backend_EmitLL.
-    if (!TheModule->getModuleFlag("EnableSplitLTOUnit"))
-      TheModule->addModuleFlag(llvm::Module::Error, "EnableSplitLTOUnit",
-                               uint32_t(CodeGenOpts.EnableSplitLTOUnit));
-    if (CodeGenOpts.UnifiedLTO && !TheModule->getModuleFlag("UnifiedLTO"))
+
+    if (shouldEmitUnifiedLTOModueFlag())
       TheModule->addModuleFlag(llvm::Module::Error, "UnifiedLTO", uint32_t(1));
   }