设置llvm :: ConstantInt的值

我正在玩LLVM。 我想过在中间代码中改变常量的值。 但是，对于类llvm :: ConstantInt ，我没有看到setvalue函数。 任何想法如何修改IR代码中常量的值？

Answer 1

ConstantInt是一家工厂，不是吗？ 类具有构造新常量的get方法 ：

/* ... return a ConstantInt for the given value. */ 00069 static Constant *get(Type *Ty, uint64_t V, bool isSigned = false); 

所以，我认为，你无法修改现有的ConstantInt。 如果要修改IR，则应尝试将指针更改为参数（更改IR本身，但不更改常量对象）。

可能你想要这样的东西（请记住，我对LLVM没有经验;我几乎可以肯定的例子是不正确的）。

 Instruction *I = /* your argument */; /* check that instruction is of needed format, eg: */ if (I->getOpcode() == Instruction::Add) { /* read the first operand of instruction */ Value *oldvalue = I->getOperand(0); /* construct new constant; here 0x1234 is used as value */ Value *newvalue = ConstantInt::get(oldValue->getType(), 0x1234); /* replace operand with new value */ I->setOperand(0, newvalue); } 

要单独“修改”常量，有一个解决方案（说明增量和减量）：

  /// AddOne - Add one to a ConstantInt. static Constant *AddOne(Constant *C) { return ConstantExpr::getAdd(C, ConstantInt::get(C->getType(), 1)); } /// SubOne - Subtract one from a ConstantInt. static Constant *SubOne(ConstantInt *C) { return ConstantInt::get(C->getContext(), C->getValue()-1); } 

PS，Constant.h在关于创建和不删除常量的请求中有重要的评论http://llvm.org/docs/doxygen/html/Constant_8h_source.html

 00035 /// Note that Constants are immutable (once created they never change) 00036 /// and are fully shared by structural equivalence. This means that two 00037 /// structurally equivalent constants will always have the same address. 00038 /// Constants are created on demand as needed and never deleted: thus clients 00039 /// don't have to worry about the lifetime of the objects. 00040 /// @brief LLVM Constant Representation