手工将一个 llvm IR 汇编代码解析成为 bitcode 文件

1，原始c语言文件

sum.c

int sum(int a, int b)
{
	return a+b;
}

2，编译成为 LLVM-IR 汇编语言

clang sum.c -emit-llvm -S -c -o sum.ll

3，手工把 llvm IR 汇编语言解析成 bitcode

3.1，源码

gen_llvm_ir.cpp

#include <llvm/ADT/SmallVector.h>
#include <llvm/IR/BasicBlock.h>
#include <llvm/IR/CallingConv.h>
#include <llvm/IR/Function.h>
#include <llvm/IR/Instructions.h>
#include <llvm/IR/LLVMContext.h>
#include <llvm/IR/Module.h>
#include <llvm/Bitcode/ReaderWriter.h>
#include <llvm/Support/FileSystem.h>
#include <llvm/Support/ToolOutputFile.h>
using namespace llvm;

//手工解析 sum.ll 成为 bitcode
Module *makeLLVMModule() 
{
	Module *mod = new Module("sum.ll", getGlobalContext());
	SmallVector<Type*, 2> FuncTyArgs;
	
	FuncTyArgs.push_back(IntegerType::get(mod->getContext(), 32));
	FuncTyArgs.push_back(IntegerType::get(mod->getContext(), 32));
	
	FunctionType *FuncTy = FunctionType::get(IntegerType::get(mod->getContext(), 32), FuncTyArgs, false);
	// define function sum return type;
	Function *funcSum =	Function::Create(FuncTy, GlobalValue::ExternalLinkage, "sum", mod);
	//define Function object
	
	funcSum->setCallingConv(CallingConv::C);
	Function::arg_iterator args = funcSum->arg_begin();
	// define arguments of sum()
	Value *int32_a = args++;
	int32_a->setName("a");
	// name the first argument
	Value *int32_b = args++;
	int32_b->setName("b");
	// name the second argument
	
	BasicBlock *labelEntry = BasicBlock::Create(mod->getContext(), "entry", funcSum, 0);
	// define entry of function 
	AllocaInst *ptrA = new AllocaInst(IntegerType::get(mod->getContext(), 32), "a.addr", labelEntry); 
	// %a.addr = alloca i32, align 4
	ptrA->setAlignment(4);
	AllocaInst *ptrB = new AllocaInst(IntegerType::get(mod->getContext(), 32), "b.addr", labelEntry); 
	// %b.addr = alloca i32, align 4
	ptrB->setAlignment(4);
	StoreInst *st0 = new StoreInst(int32_a, ptrA, false, labelEntry);
	// store i32 %a, i32* %a.addr, align 4
	st0->setAlignment(4);
	StoreInst *st1 = new StoreInst(int32_b, ptrB, false, labelEntry);
	// store i32 %b, i32* %b.addr, align 4
	st1->setAlignment(4);
	LoadInst *ld0 = new LoadInst(ptrA, "", false, labelEntry);
	// %0 = load i32* %a.addr, align 4
	ld0->setAlignment(4);
	LoadInst *ld1 = new LoadInst(ptrB, "", false, labelEntry);
	// %1 = load i32* %b.addr, align 4
	ld1->setAlignment(4);
	BinaryOperator *addRes = BinaryOperator::Create(Instruction::Add, ld0, ld1,	"add", labelEntry);
	//%add = add msw i32 %0, %1
	ReturnInst::Create(mod->getContext(), addRes, labelEntry);
	// ret i32 %add
	
	return mod;
}

int main(int argc, char **argv) 
{
	Module *Mod = makeLLVMModule();
	std::string ErrorInfo;
	std::unique_ptr<tool_output_file> Out(new tool_output_file("./sum.bc", ErrorInfo, sys::fs::F_None));
	if (!ErrorInfo.empty()) {
		errs() << ErrorInfo << "\n";
		return -1;
	}
	WriteBitcodeToFile(Mod, Out->os());
	Out->keep();
	
	return 0;
}

Makefile

LLVM_CONFIG ?= llvm-config
#CXX := clang++
ifndef VERBOSE
QUIET :=@
endif

SRC_DIR ?= $(PWD)
LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags) 
COMMON_FLAGS = -Wall -Wextra
CXXFLAGS += $(COMMON_FLAGS) $(shell $(LLVM_CONFIG) --cxxflags)
LCXX :=$(shell $(LLVM_CONFIG) --cxxflags)
CPPFLAGS += $(shell $(LLVM_CONFIG) --cppflags) -I$(SRC_DIR)

CLANGLIBS = \
  -Wl,--start-group \
  -lclang \
  -lclangFrontend \
  -lclangDriver \
  -lclangSerialization \
  -lclangParse \
  -lclangSema \
  -lclangAnalysis \
  -lclangEdit \
  -lclangAST \
  -lclangLex \
  -lclangBasic \
  -Wl,--end-group

LLVMLIBS = $(shell $(LLVM_CONFIG) --libs)

PROJECT = gen_llvm_ir
PROJECT_OBJECTS = gen_llvm_ir.o

default: $(PROJECT)

%.o : $(SRC_DIR)/%.cpp
	@echo Compiling $*.cpp
	$(QUIET)$(CXX) -c $(CPFLAGS) $(CXXFLAGS) $<

$(PROJECT) : $(PROJECT_OBJECTS) 
	@echo Linking $@
	$(QUIET)$(CXX) -o $@ $(LDFLAGS) $^ $(CLANGLIBS) $(LLVMLIBS) -lncurses

.PHONY: clean
clean:
	$(QUIET)rm -f $(PROJECT) $(PROJECT_OBJECTS)


.PHONY: echo
echo:
	@echo "CXX 	is	$(CXX)"
	@echo "LDFLAGS 	is	$(LDFLAGS)}"
	@echo "CXXFLAGS	is	$(CXXFLAGS)"
	@echo "CPPFLAGS	is	$(CPPFLAGS)"
	@echo "SRC_DIR	is	$(SRC_DIR)"