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

[Dean Michael Berris via llvm-dev]

> On 5 Sep 2016, at 11:49, SHUCAI YAO <yaos4 at mcmaster.ca> wrote:
> 
> For the function call lowering, do you mean lowercall function? I did insert the instruction before the stack adjustments, but the inserted code appears in the prologue of the function, other than before the function call. Maybe I did something wrong with the iterator. 
> 
> So you mean I should insert a pseudo instruction in the machinefunction pass, then replace it when function call lowering?  (Like segemented stack implementation?)
> 

Yes, inserting pseudo instructions in the MachineFunctionPass -- you might want to have a look at PATCHABLE_RET and how we handle this in XRay. Essentially the idea (which I saw Sanjoy Das do first) is to wrap the actual instruction (in this case, CALL or LEA, or something specific in the platform you're targeting) in a pseudo instruction that just lowers to the correct sequence. This gives you complete control of the actual assembly of the instructions that you're replacing.

-- Dean