一：前端

#include <iostream>
#include <algorithm>
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/MemoryBuffer.h"class Lexer;class Token{friend class Lexer;
public:enum TokenKind: unsigned short{eoi, //end of inputunknown, //error of inputident, //[a-zA-Z]number,//[0-9]comma, //,colon, //:plus, //+minus, //-start, //'*'slash, //'/'l_paren, //'('r_paren, //')'KW_with, //with};
private:TokenKind  Kind;llvm::StringRef Text;
public:TokenKind getKind() const {return Kind; }llvm::StringRef getText() const {return Text; }bool is(TokenKind K) const {return Kind ==K; }bool isOneOf(TokenKind K1, TokenKind K2) const {return is(K1) || is(K2); }template<typename... Ts> bool isOneOf(TokenKind K1, TokenKind K2, Ts... Ks) const { return is(K1)||isOneof(K2, Ks...);}
};class Lexer{const char *BufferStart;const char *BufferPtr;public:Lexer(const llvm::StringRef &Buffer) {BufferStart = Buffer.begin();BufferPtr = BufferStart;}void next(Token &token){while(*BufferPtr != '\0' && std::iswspace(*BufferPtr)){++BufferPtr;}if(!*BufferPtr){token.Kind = Token::eoi;return;}if(std::isalpha(*BufferPtr)){const char *end = BufferPtr + 1;while(std::isalpha(*end)){++end;}llvm::StringRef Name(BufferPtr, end - BufferPtr);Token::TokenKind kind = Name == "with" ? Token::KW_with : Token::ident;fromToken(token, end, kind);return;}else if (std::isdigit(*BufferPtr)){const char *end = BufferPtr + 1;while(std::isdigit(*end)){++end;}fromToken(token, end, Token::number);return;}else {switch(*BufferPtr){case ',': token.Kind = Token::comma; break;case ':': token.Kind = Token::colon; break;case '+': token.Kind = Token::plus; break;case '-': token.Kind = Token::minus; break;case '*': token.Kind = Token::start; break;case '/': token.Kind = Token::slash; break;case '(': token.Kind = Token::l_paren; break;case ')': token.Kind = Token::r_paren; break;default: token.Kind = Token::unknown; break;}fromToken(token, BufferPtr + 1, token.Kind);return;}}
private:void fromToken(Token &Result, const char *TokenEnd, Token::TokenKind Kind){Result.Kind = Kind;Result.Text = llvm::StringRef(BufferPtr, TokenEnd - BufferPtr);BufferPtr = TokenEnd;}
};int main()
{/*with a, b: a * (4 + b)with a: a * 3*/std::cout << "Welcome to the " << __FILE__ <<std::endl;
}//CMakeLists.txt 
/*
cmake_minimum_required(VERSION 3.16.0)set(NAME "learn_llvm")
project(${NAME})set(CMAKE_CXX_STANDARD 20) # this does nothing for MSVC, use target_compile_options below
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS ON)
set(CMAKE_BUILD_TYPE Debug)find_package(LLVM REQUIRED CONFIG)message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")# Set your project compile flags.
# E.g. if using the C++ header files
# you will need to enable C++11 support
# for your compiler.include_directories(${LLVM_INCLUDE_DIRS})
message(STATUS ${LLVM_INCLUDE_DIRS})
separate_arguments(LLVM_DEFINITIONS_LIST NATIVE_COMMAND ${LLVM_DEFINITIONS})
add_definitions(${LLVM_DEFINITIONS_LIST})# Now build our tools
set(SOURCE main.cpp)
add_executable(${NAME} ${SOURCE})# Find the libraries that correspond to the LLVM components
# that we wish to use
llvm_map_components_to_libnames(llvm_libs support core irreader)# Link against LLVM libraries
target_link_libraries(${NAME} ${llvm_libs})
*/

二：中端

三：后端