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Re: patch to improve i386 epilogue (version 2)
- To: John Wehle <john at feith dot com>
- Subject: Re: patch to improve i386 epilogue (version 2)
- From: Jeffrey A Law <law at cygnus dot com>
- Date: Sat, 19 Sep 1998 23:10:35 -0600
- cc: egcs-patches at cygnus dot com
- Reply-To: law at cygnus dot com
In message <199809190707.DAA01442@jwlab.FEITH.COM>you write:
> [ The change to jump.c is the only difference from the previous
> version of this patch. ]
> This change allows gcc to skip the loading of the stack pointer
> when it is already known to contain the proper value. This
> optimization is currently only implemented for leaf functions.
I suspect your call counts are still going to be inaccurate -- for
example flow.c can/will delete calls if they are in an unreachable
block without calling delete_insn.
There may be other cases where this can happen too -- we'd really
need to read all of the optimizers a little more closely.
Also, don't we have to be careful with the value changing over time?
ie, what happens if at prologue generation time we think there is a
call, but due to some optimization after reload we end up deleting
a call (can this happen?!?) and leaf_function_p returns true.
Presumably you aren't calling leaf_function_p in the epilogue expander
because we've already got a sequence started and thus we can't get to
the original insn chain?
Maybe it would be better to pass in a variable to the prologue/epilogue
expanders indicating whether or not the current function is a leaf
function. An interface change for the md files, but a relatively minor
I like the idea though. It mirrors something I did for the mn10x
series before I made ACCUMULATE_OUTGOING_ARGS work for more targets.
The basic idea was we could eliminate the frame pointer in any
function which didn't make function calls.