* Help with the disassembly of a very short function, please.
@ 2022-01-01 19:01 Alan Mackenzie
2022-01-01 19:43 ` Andreas Schwab
0 siblings, 1 reply; 3+ messages in thread
From: Alan Mackenzie @ 2022-01-01 19:01 UTC (permalink / raw)
To: emacs-devel
Hello, Emacs.
The following function comes from .../test/src/comp-tests.el, more or
less:
;; -*- lexical-binding: t -*-
(defun comp-test-55 (x)
(unless (integerp x)
x))
I byte compile it with C-x C-e then dump out its byte code with M-x
disassemble. I get this:
byte code for comp-test-55:
doc: ...
args: (arg1)
0 dup
1 integerp
2 not
3 goto-if-nil-else-pop 1
6 dup
7:1 return
.. In the case where x is not an integer, it seems that the dup at 6
will leave two many copies of x on the stack for the return.
In the case where x is an integer, it seems that the
goto-if-nil-else-pop will leave a nil on the stack over the original
x, returning the nil but leaving a superfluous copy of the integer x
on the stack.
So, either way, there is an unwanted copy of x left on the stack at the
end of the function.
I can't work this out. What am I missing?
--
Alan Mackenzie (Nuremberg, Germany).
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Help with the disassembly of a very short function, please.
2022-01-01 19:01 Help with the disassembly of a very short function, please Alan Mackenzie
@ 2022-01-01 19:43 ` Andreas Schwab
2022-01-01 22:07 ` Alan Mackenzie
0 siblings, 1 reply; 3+ messages in thread
From: Andreas Schwab @ 2022-01-01 19:43 UTC (permalink / raw)
To: Alan Mackenzie; +Cc: emacs-devel
The arguments are not consumed. Each byte-code execution has a private
value stack, which is just discarded at the end, no matter what's left.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
"And now for something completely different."
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: Help with the disassembly of a very short function, please.
2022-01-01 19:43 ` Andreas Schwab
@ 2022-01-01 22:07 ` Alan Mackenzie
0 siblings, 0 replies; 3+ messages in thread
From: Alan Mackenzie @ 2022-01-01 22:07 UTC (permalink / raw)
To: Andreas Schwab; +Cc: emacs-devel
Hello, Andreas.
On Sat, Jan 01, 2022 at 20:43:52 +0100, Andreas Schwab wrote:
> The arguments are not consumed. Each byte-code execution has a private
> value stack, which is just discarded at the end, no matter what's left.
Thanks, I understand it now.
> --
> Andreas Schwab, schwab@linux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
> "And now for something completely different."
--
Alan Mackenzie (Nuremberg, Germany).
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-01-01 19:01 Help with the disassembly of a very short function, please Alan Mackenzie
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