[llvm-dev] Can we keep debug information of local variable when in the optimization condition?

[Wu Zhao via llvm-dev]

Hi, I'm curious that whether we can keep debug information of local variable when in the optimization condition (for example -O2, -O3) in LLVM.


For example this simple C source code:


int main()
{
    int i = 5;
    if(i > 5) {
        return 1;
    } else {
        return 0;
    }
}


If we compile clang -g a.c, we can get our expected result. We can check and update the local variable i in the debugger.

However, when we compile it using clang -O3 -g a.c, we can only check the variable i but we can not  update the local variable i.

I know, the design of LLVM opt-debug is that debug can not affect optimization, so this case llvm-opt will turn the llvm.dbg.declare and related alloc / store instruction to llvm.dbg.value, we don't have symbol of local variable i. So we can only check local variable i but we can not update the value of local variable i like set variable i = 7 in the gdb.

I think keep debug information of local variable in some condition is very useful and I want to explore it. However, I find there are many places do this work of local variable debug info. I want to know whether I have one simple way like disabling some passes or modify some llvm code to continue this way.

Thanks in advance. 
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