[C API] Add LLVMWriteThinLTOBitcodeToMemoryBuffer to C API

[aykevl]

Summary

A similar function already exists in Rust as LLVMRustThinLTOBufferCreate. I needed it in the C API for my own project so I wrote this patch to add it.

I tried using the new pass manager, but somehow that didn't work: no module summary was created.

This didn't work:

std::string Data;
raw_string_ostream OS(Data);
ModulePassManager MPM;
ModuleAnalysisManager MAM;
MPM.addPass(ThinLTOBitcodeWriterPass(OS, nullptr));
MPM.run(*unwrap(M), MAM);
return wrap(MemoryBuffer::getMemBufferCopy(OS.str()).release());

[aykevl]

• add Go API

[aykevl]

• fix

[aykevl]

ping

[deadalnix]

Hi @aykevl . I unfortunately am not familiar with thin LTO, so it is very difficult for me to review this. Maybe @mehdi_amini could help? I know he worked on this at some point, and if he cannot, he'll know who can.

llvm/bindings/go/llvm/bitwriter.go

func WriteBitcodeToFile(m Module, file *os.File) error {
   return nil
 }
 
 func WriteBitcodeToMemoryBuffer(m Module) MemoryBuffer {
   mb := C.LLVMWriteBitcodeToMemoryBuffer(m.C)
   return MemoryBuffer{mb}
 }
 
+func WriteThinLTOBitcodeToMemoryBuffer(m Module) MemoryBuffer {
+  mb := C.LLVMWriteThinLTOBitcodeToMemoryBuffer(m.C)
+  return MemoryBuffer{mb}
+}
+
 // TODO(nsf): Figure out way how to make it work with io.Writer

llvm/include/llvm-c/BitWriter.h

 
 /** Deprecated for LLVMWriteBitcodeToFD. Writes a module to an open file
     descriptor. Returns 0 on success. Closes the Handle. */
 int LLVMWriteBitcodeToFileHandle(LLVMModuleRef M, int Handle);
 
 /** Writes a module to a new memory buffer and returns it. */
 LLVMMemoryBufferRef LLVMWriteBitcodeToMemoryBuffer(LLVMModuleRef M);
 
+/** Writes a module with ThinLTO summary to a new memory buffer and returns it. */
+LLVMMemoryBufferRef LLVMWriteThinLTOBitcodeToMemoryBuffer(LLVMModuleRef M);
+
 /**
  * @}
  */
 
 LLVM_C_EXTERN_C_END
 
 #endif

llvm/lib/Bitcode/Writer/BitWriter.cpp

 //===-- BitWriter.cpp -----------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm-c/BitWriter.h"
 #include "llvm/Bitcode/BitcodeWriter.h"
+#include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/IPO.h"
 using namespace llvm;
 
 
 /*===-- Operations on modules ---------------------------------------------===*/
 
 int LLVMWriteBitcodeToFile(LLVMModuleRef M, const char *Path) {
   std::error_code EC;
   raw_fd_ostream OS(Path, EC, sys::fs::OF_None);

 
 LLVMMemoryBufferRef LLVMWriteBitcodeToMemoryBuffer(LLVMModuleRef M) {
   std::string Data;
   raw_string_ostream OS(Data);
 
   WriteBitcodeToFile(*unwrap(M), OS);
   return wrap(MemoryBuffer::getMemBufferCopy(OS.str()).release());
 }
+
+LLVMMemoryBufferRef LLVMWriteThinLTOBitcodeToMemoryBuffer(LLVMModuleRef M) {
+  std::string Data;
+  llvm::raw_string_ostream OS(Data);
+  llvm::legacy::PassManager PM;
+  PM.add(createWriteThinLTOBitcodePass(OS));
+  PM.run(*llvm::unwrap(M));
+  return llvm::wrap(llvm::MemoryBuffer::getMemBufferCopy(OS.str()).release());
+}