[LLVM_IR]GenerateIfElseIR

#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Verifier.h"
#include 
using namespace llvm;

static LLVMContext Context;
static Module* ModuleOb = new Module ( "my compiler", Context );
static std::vector FunArgs;
typedef SmallVector BBList;
typedef SmallVector ValList;

Function* createFunc ( IRBuilder<>& Builder, std::string Name ) {
    std::vector Integers ( FunArgs.size(), Type::getInt32Ty ( Context ) );
    FunctionType* funcType =
        llvm::FunctionType::get ( Builder.getInt32Ty(), Integers, false );
    Function* fooFunc = llvm::Function::Create (
            funcType, llvm::Function::ExternalLinkage, Name, ModuleOb );
    return fooFunc;
}

void setFuncArgs ( Function* fooFunc, std::vector FunArgs ) {
    unsigned Idx = 0;
    Function::arg_iterator AI, AE;

    for ( AI = fooFunc->arg_begin(), AE = fooFunc->arg_end(); AI != AE;
        ++AI, ++Idx )
        AI->setName ( FunArgs[Idx] );
}

BasicBlock* createBB ( Function* fooFunc, std::string Name ) {
    return BasicBlock::Create ( Context, Name, fooFunc );
}

GlobalVariable* createGlob ( IRBuilder<>& Builder, std::string Name ) {
    ModuleOb->getOrInsertGlobal ( Name, Builder.getInt32Ty() );
    GlobalVariable* gVar = ModuleOb->getNamedGlobal ( Name );
    gVar->setLinkage ( GlobalValue::CommonLinkage );
    gVar->setAlignment ( 4 );
    return gVar;
}

Value* createArith ( IRBuilder<>& Builder, Value* L, Value* R ) {
    return Builder.CreateMul ( L, R, "multmp" );
}

Value* createIfElse ( IRBuilder<>& Builder, BBList List, ValList VL ) {
    Value* Condtn = VL[0];
    Value* Arg1 = VL[1];
    BasicBlock* ThenBB = List[0];
    BasicBlock* ElseBB = List[1];
    BasicBlock* MergeBB = List[2];
    Builder.CreateCondBr ( Condtn, ThenBB, ElseBB );
    Builder.SetInsertPoint ( ThenBB );
    Value* ThenVal = Builder.CreateAdd ( Arg1, Builder.getInt32 ( 1 ), "thenaddtmp" );
    Builder.CreateBr ( MergeBB );
    Builder.SetInsertPoint ( ElseBB );
    Value* ElseVal = Builder.CreateAdd ( Arg1, Builder.getInt32 ( 2 ), "elseaddtmp" );
    Builder.CreateBr ( MergeBB );
    unsigned PhiBBSize = List.size() - 1;
    Builder.SetInsertPoint ( MergeBB );
    PHINode* Phi = Builder.CreatePHI ( Type::getInt32Ty ( Context ),
            PhiBBSize, "iftmp" );
    Phi->addIncoming ( ThenVal, ThenBB );
    Phi->addIncoming ( ElseVal, ElseBB );
    return Phi;
}

int main ( int argc, char* argv[] ) {
    FunArgs.push_back ( "a" );
    FunArgs.push_back ( "b" );
    static IRBuilder<> Builder ( Context );
    GlobalVariable* gVar = createGlob ( Builder, "x" );
    Function* fooFunc = createFunc ( Builder, "foo" );
    setFuncArgs ( fooFunc, FunArgs );
    BasicBlock* entry = createBB ( fooFunc, "entry" );
    Builder.SetInsertPoint ( entry );
    Function::arg_iterator Args = fooFunc->arg_begin();
    Value* Arg1 = &*Args++;
    Value* constant = Builder.getInt32 ( 16 );
    Value* val = createArith ( Builder, Arg1, constant );
    Value* val2 = Builder.getInt32 ( 100 );
    Value* Compare = Builder.CreateICmpULT ( val, val2, "cmptmp" );
    // Value *Condtn = Builder.CreateICmpNE(Compare, Builder.getInt32(0),
    // "ifcond");
    ValList VL;
    VL.push_back ( Compare );
    VL.push_back ( Arg1 );
    BasicBlock* ThenBB = createBB ( fooFunc, "then" );
    BasicBlock* ElseBB = createBB ( fooFunc, "else" );
    BasicBlock* MergeBB = createBB ( fooFunc, "ifcont" );
    BBList List;
    List.push_back ( ThenBB );
    List.push_back ( ElseBB );
    List.push_back ( MergeBB );
    Value* v = createIfElse ( Builder, List, VL );
    Builder.CreateRet ( v );
    verifyFunction ( *fooFunc );
    ModuleOb->dump();
    return 0;
}