[clang][CodeGen] Omit pre-opt link when post-opt is link requested (#85672)

Currently, when the -relink-builtin-bitcodes-postop option is used we
link builtin bitcodes twice: once before optimization, and again after
optimization.

With this change, we omit the pre-opt linking when the option is set,
and we rename the option to the following:

  -Xclang -mlink-builtin-bitcodes-postopt
 (-Xclang -mno-link-builtin-bitcodes-postopt) 

The goal of this change is to reduce compile time. We do lose the
theoretical benefits of pre-opt linking, but in practice these are small
than the overhead of linking twice. However we may be able to address
this in a future patch by adjusting the position of the builtin-bitcode
linking pass.

Compilations not setting the option are unaffected

1 files changed, 2 insertions, 35 deletions

diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
index 1a6b628..0255f05 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -60,10 +60,6 @@ using namespace llvm;
 
 #define DEBUG_TYPE "codegenaction"
 
-namespace llvm {
-extern cl::opt<bool> ClRelinkBuiltinBitcodePostop;
-}
-
 namespace clang {
 class BackendConsumer;
 class ClangDiagnosticHandler final : public DiagnosticHandler {
@@ -232,35 +228,6 @@ void BackendConsumer::HandleInterestingDecl(DeclGroupRef D) {
     HandleTopLevelDecl(D);
 }
 
-bool BackendConsumer::ReloadModules(llvm::Module *M) {
-  for (const CodeGenOptions::BitcodeFileToLink &F :
-       CodeGenOpts.LinkBitcodeFiles) {
-    auto BCBuf = FileMgr.getBufferForFile(F.Filename);
-    if (!BCBuf) {
-      Diags.Report(diag::err_cannot_open_file)
-          << F.Filename << BCBuf.getError().message();
-      LinkModules.clear();
-      return true;
-    }
-
-    LLVMContext &Ctx = getModule()->getContext();
-    Expected<std::unique_ptr<llvm::Module>> ModuleOrErr =
-        getOwningLazyBitcodeModule(std::move(*BCBuf), Ctx);
-
-    if (!ModuleOrErr) {
-      handleAllErrors(ModuleOrErr.takeError(), [&](ErrorInfoBase &EIB) {
-        Diags.Report(diag::err_cannot_open_file) << F.Filename << EIB.message();
-      });
-      LinkModules.clear();
-      return true;
-    }
-    LinkModules.push_back({std::move(ModuleOrErr.get()), F.PropagateAttrs,
-                           F.Internalize, F.LinkFlags});
-  }
-
-  return false; // success
-}
-
 // Links each entry in LinkModules into our module.  Returns true on error.
 bool BackendConsumer::LinkInModules(llvm::Module *M, bool ShouldLinkFiles) {
   for (auto &LM : LinkModules) {
@@ -362,7 +329,7 @@ void BackendConsumer::HandleTranslationUnit(ASTContext &C) {
   }
 
   // Link each LinkModule into our module.
-  if (LinkInModules(getModule()))
+  if (!CodeGenOpts.LinkBitcodePostopt && LinkInModules(getModule()))
     return;
 
   for (auto &F : getModule()->functions()) {
@@ -1232,7 +1199,7 @@ void CodeGenAction::ExecuteAction() {
                          std::move(LinkModules), *VMContext, nullptr);
 
   // Link in each pending link module.
-  if (Result.LinkInModules(&*TheModule))
+  if (!CodeGenOpts.LinkBitcodePostopt && Result.LinkInModules(&*TheModule))
     return;
 
   // PR44896: Force DiscardValueNames as false. DiscardValueNames cannot be