Add ThinLTO summary support

backports.cpp

@@ -1,6 +1,10 @@
 
 #include "backports.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/LegacyPassManager.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/IPO/PassManagerBuilder.h"
 #include "llvm/Transforms/Coroutines.h"
 #include "llvm-c/DebugInfo.h"
@@ -62,3 +66,13 @@ LLVMMetadataRef LLVMGoDIBuilderCreateCompileUnit(
     SplitNameLen, Kind, DWOId, SplitDebugInlining, DebugInfoForProfiling);
 #endif
 }
+
+// See https://reviews.llvm.org/D119431
+LLVMMemoryBufferRef LLVMGoWriteThinLTOBitcodeToMemoryBuffer(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());
+}

backports.h

@@ -26,6 +26,8 @@ LLVMMetadataRef LLVMGoDIBuilderCreateCompileUnit(
     LLVMBool DebugInfoForProfiling, const char *SysRoot, size_t SysRootLen,
     const char *SDK, size_t SDKLen);
 
+LLVMMemoryBufferRef LLVMGoWriteThinLTOBitcodeToMemoryBuffer(LLVMModuleRef M);
+
 #ifdef __cplusplus
 }
 #endif /* defined(__cplusplus) */

bitwriter.go

@@ -14,6 +14,7 @@ package llvm
 
 /*
 #include "llvm-c/BitWriter.h"
+#include "backports.h"
 #include <stdlib.h>
 */
 import "C"
@@ -35,4 +36,9 @@ func WriteBitcodeToMemoryBuffer(m Module) MemoryBuffer {
 	return MemoryBuffer{mb}
 }
 
+func WriteThinLTOBitcodeToMemoryBuffer(m Module) MemoryBuffer {
+	mb := C.LLVMGoWriteThinLTOBitcodeToMemoryBuffer(m.C)
+	return MemoryBuffer{mb}
+}
+
 // TODO(nsf): Figure out way how to make it work with io.Writer