在LLVM pass中，给出一个使用branchinst插入if-then逻辑的使用示例

以下是一个使用BranchInst插入if-then逻辑的示例：

#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;

namespace {
  struct MyPass : public FunctionPass {
    static char ID;
    MyPass() : FunctionPass(ID) {}

    bool runOnFunction(Function &F) override {
      // Get the entry basic block of the function
      BasicBlock &entry = F.getEntryBlock();

      // Create the basic blocks for the if-then logic
      LLVMContext &ctx = F.getParent()->getContext();
      BasicBlock *ifBB = BasicBlock::Create(ctx, "ifBB", &F);
      BasicBlock *thenBB = BasicBlock::Create(ctx, "thenBB", &F);

      // Insert a branch instruction to the if block
      IRBuilder<> builder(&entry);
      builder.CreateBr(ifBB);

      // Build the condition for the if-then logic
      builder.SetInsertPoint(ifBB);
      Value *cond = builder.getInt1(true); // Replace with your own condition

      // Insert a conditional branch instruction to either then or exit
      builder.CreateCondBr(cond, thenBB, &entry);

      // Build the instructions for the then block
      builder.SetInsertPoint(thenBB);
      builder.CreateRetVoid(); // Replace with your own instructions

      return true;
    }
  };
}

char MyPass::ID = 0;
static RegisterPass<MyPass> X("my-pass", "My LLVM Pass");

该示例将在函数的入口基本块中插入一个无条件分支到if基本块。然后，它使用IRBuilder创建if和then基本块，并在if基本块中插入一个条件分支指令，根据条件跳转到then基本块或退出基本块。最后，它在then基本块中插入一些指令（在本例中只是一个返回void语句）。

请注意，示例中的条件始终为真，因此将始终跳转到then基本块。您需要将其替换为您自己的条件。