[llvm-dev] How to insert instructions before each function calls?

Mehdi Amini via llvm-dev llvm-dev at lists.llvm.org
Sat Sep 3 22:45:25 PDT 2016

> On Sep 3, 2016, at 6:18 PM, Ryan Taylor via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> So one way might look like this:
> IRBuilder<> Builder(&*BB); // BB = Function::iterator OR IRBuilder<> Builder(CallInst->getParent());
> Builder.SetInsertPoint(CallInst);
> InstructionClass *YourNewInstruction = builder.CreateInstructionClass(.....); // InstructionClass = type of instruction you are inserting

I’m not sure how the IRBuilder would work at the MI level, as Shucai was asking.

> On Sat, Sep 3, 2016 at 6:04 PM, Ryan Taylor <ryta1203 at gmail.com <mailto:ryta1203 at gmail.com>> wrote:
> Take a look at IRBuilder and SetInsertPoint().
> On Sep 3, 2016 18:02, "SHUCAI YAO via llvm-dev" <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> I'm trying to insert some instructions before each function calls (before arguments push):
>    lea %EAX, label                      ----- new instructions
>    mov [ESP+stacksize], %EAX  ----- new instructions
>    push arg1
>    push arg2
>    ...
>    push argn
>    call callee_name
> I am a newbie to LLVM. I tried to use buildMI() to insert the instructions in the lowercall() function. But I couldn't put these instructions in the right positions. Is there a way to locate the position by using MachineBasicBlock iterator?

Can you describe more precisely what are you trying to achieve?
I.e. what are these instructions? Why do you want to do that? It may lead to a different answer.

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