SKIP_PROLOGUE() and prologue insn scheduling

[Kevin Buettner]

On Jul 17,  3:46pm, J.T. Conklin wrote:

> A coworker asked me what the prefered behavior of the SKIP_PROLOGUE()
> macro when the compiler schedules the function prologue in with user
> insns.  I didn't have a good answer and the internals documentation
> doesn't address this, so I'm shooting the question to the list.
> 
> The choice is whether SKIP_PROLOGUE() returns:
>     1) 1st user insn even though more prologue insns remain?
>     2) 1st user insn after final prologue insn?
> 
> Of these two, I think #1 is the most conservative choice.  However,
> gdb may may not be able to print function arguments correctly until
> the user steps beyond the remainder of the prologue.  While #2 does
> not have that problem, having user insns execute as part of the
> prologue could also be confusing --- Especially those that have
> observable side effects (e.g. writes to a memory mapped device).
> 
> What is the common wisdom?  At the very least, I think we need to
> flesh out this issue in the internals document.

In the prologue scanners that I've worked on, I've tried to implement
option #2.

Kevin