[ThinLTO] Make -lto-embed-bitcode an enum

The current behavior of -lto-embed-bitcode is not quite the same as that
of -fembed-bitcode. While both populate .llvmbc with bitcode, the latter
populates it with pre-optimized bitcode(*), while the former with
post-optimized. The scenarios driving them are different - the latter's
goal is to allow re-compilation, while the former, IIUC, is execution.

I plan to add a third mode for thinlto cases, closely-related to
-fembed-bitcode's scenario: adding the bitcode pre-optimization, but
post-merging. This would allow re-compilation without requiring the
other .bc files that were merged (akin to how -fembed-bitcode allows
recompilation without all the .h files)

The third mode can't co-exist with the current -lto-embed-bitcode mode,
because the latter would overwrite it. For clarity, we change
-lto-embed-bitcode to be an enum.

(*) That's the compiler semantics. The driver splits compilation in 2
phases, so if -fembed-bitcode is given to the driver, the .llvmbc is
optimized bitcode; if the option is passed to the compiler (after -cc1),
the section is pre-optimized.

Differential Revision: https://reviews.llvm.org/D87477

1 files changed, 17 insertions, 12 deletions

diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
index 966edcf..00309b6 100644
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -50,6 +50,19 @@
 using namespace llvm;
 using namespace lto;
 
+enum class LTOBitcodeEmbedding {
+  DoNotEmbed = 0,
+  EmbedOptimized = 1,
+};
+
+static cl::opt<LTOBitcodeEmbedding> EmbedBitcode(
+    "lto-embed-bitcode", cl::init(LTOBitcodeEmbedding::DoNotEmbed),
+    cl::values(clEnumValN(LTOBitcodeEmbedding::DoNotEmbed, "none",
+                          "Do not embed"),
+               clEnumValN(LTOBitcodeEmbedding::EmbedOptimized, "optimized",
+                          "Embed after all optimization passes")),
+    cl::desc("Embed LLVM bitcode in object files produced by LTO"));
+
 LLVM_ATTRIBUTE_NORETURN static void reportOpenError(StringRef Path, Twine Msg) {
   errs() << "failed to open " << Path << ": " << Msg << '\n';
   errs().flush();
@@ -346,24 +359,16 @@ bool opt(const Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
   return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
 }
 
-static cl::opt<bool> EmbedBitcode(
-    "lto-embed-bitcode", cl::init(false),
-    cl::desc("Embed LLVM bitcode in object files produced by LTO"));
-
-static void EmitBitcodeSection(Module &M) {
-  if (!EmbedBitcode)
-    return;
-  llvm::EmbedBitcodeInModule(M, llvm::MemoryBufferRef(), /*EmbedBitcode*/ true,
-                             /*EmbedMarker*/ false, /*CmdArgs*/ nullptr);
-}
-
 void codegen(const Config &Conf, TargetMachine *TM, AddStreamFn AddStream,
              unsigned Task, Module &Mod,
              const ModuleSummaryIndex &CombinedIndex) {
   if (Conf.PreCodeGenModuleHook && !Conf.PreCodeGenModuleHook(Task, Mod))
     return;
 
-  EmitBitcodeSection(Mod);
+  if (EmbedBitcode == LTOBitcodeEmbedding::EmbedOptimized)
+    llvm::EmbedBitcodeInModule(Mod, llvm::MemoryBufferRef(),
+                               /*EmbedBitcode*/ true,
+                               /*EmbedMarker*/ false, /*CmdArgs*/ nullptr);
 
   std::unique_ptr<ToolOutputFile> DwoOut;
   SmallString<1024> DwoFile(Conf.SplitDwarfOutput);