thinlto: only build summary file if needed

If we don't do this, some versions of LLVM (at least 17, experimentally)
will double-emit some error messages, which is how I noticed this. Given
that it seems to be costing some extra work, let's only request the
summary bitcode production if we'll actually bother writing it down,
otherwise skip it.

1 files changed, 5 insertions, 2 deletions

diff --git a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
index c210d2531e7..3fcf3aca8af 100644
--- a/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp
@@ -1492,7 +1492,7 @@ struct LLVMRustThinLTOBuffer {
 };
 
 extern "C" LLVMRustThinLTOBuffer*
-LLVMRustThinLTOBufferCreate(LLVMModuleRef M, bool is_thin) {
+LLVMRustThinLTOBufferCreate(LLVMModuleRef M, bool is_thin, bool emit_summary) {
   auto Ret = std::make_unique<LLVMRustThinLTOBuffer>();
   {
     auto OS = raw_string_ostream(Ret->data);
@@ -1510,7 +1510,10 @@ LLVMRustThinLTOBufferCreate(LLVMModuleRef M, bool is_thin) {
         PB.registerLoopAnalyses(LAM);
         PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
         ModulePassManager MPM;
-        MPM.addPass(ThinLTOBitcodeWriterPass(OS, &ThinLinkOS));
+        // We only pass ThinLinkOS to be filled in if we want the summary,
+        // because otherwise LLVM does extra work and may double-emit some
+        // errors or warnings.
+        MPM.addPass(ThinLTOBitcodeWriterPass(OS, emit_summary ? &ThinLinkOS : nullptr));
         MPM.run(*unwrap(M), MAM);
       } else {
         WriteBitcodeToFile(*unwrap(M), OS);