Re: SKIP_PROLOGUE() and prologue insn scheduling

Greg McGary
2001-07-18T09:31:00Z

Daniel Jacobowitz <dmj+@andrew.cmu.edu> writes:

> > 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?
> [ ... ]
> IMO, #1 is the way to go. It's regrettable in that a whole lot of
> tests start failing, since we will display arguments wrong. But if the
> prologue is being scheduled, it's possible to schedule part of the
> prologue on the interior of a large if statement (which encompasses the
> rest of the body of the function, say). If we do #2, we may never stop
> in the function at all.

That particular pathology should not occur. First, the RTL for
prologue & epilogue is not generated until the flow2 pass, rather late
in the game, and after such code motion could occur. Second,
SKIP_PROLOGUE() must be written to stop scanning for prologue insns
when it reaches the end of the first basic block, as demarcated by a
jump or branch insn. Therefore, #2 remains a viable option as we
would never place the breakpoint in conditionally-executed code.

Greg