Re: [PATCH] final: Improve output for -dp and -fverbose-asm

[Martin Sebor <msebor@gmail.com>]

On 11/30/2017 04:16 AM, Segher Boessenkool wrote:
> On Wed, Nov 29, 2017 at 08:46:41PM -0700, Martin Sebor wrote:
>> On 11/29/2017 04:13 PM, Segher Boessenkool wrote:
>>> This improves the assembler output (for -dp and -fverbose-asm) in
>>> several ways.  It always prints the insn_cost.  It does not print
>>> "[length = NN]" but "[c=NN l=NN]", to save space.  It does not add one
>>> to the instruction alternative number (everything else starts counting
>>> those at 0, too).  And finally, it tries to keep things lined up in
>>> columns a bit better.
>>>
>>> Tested on powerpc64-linux {-m32,-m64}; is this okay for trunk?
>>
>> [c=NN l=NN] will be meaningless to those without some deeper
>> insight into/experience with what's actually being printed.
>> It might as well say [NN NN].  But such extreme terseness would
>
> Length isn't printed on all targets, fwiw.
>
>> seem to run counter to the documented purpose of -fverbose-asm
>> to "Put extra commentary information in the generated assembly
>> code to make it more readable."
>
> The point is that [length = 12] takes up an awful lot of space.  The
> output of -fverbose-asm alread suffers from information overload.

Amount of space vs amount of detail are two different concerns.
If you feel that the output is overly detailed then adding even
more to it won't help.  Other than that, I don't think trading
readability for space savings makes sense in a format whose main
purpose is to be readable.  If it's line length that's a concern
then using spaces instead of tabs would make them look shorter.
You can also remove the brackets and use length=NN to shave off
a couple of bytes.  Or print length only when it's not the typical
default.  Or print the hex encoding instead.

>> Looking further in the manual I don't see the [length=NN] bit
>> mentioned (nor does your patch add a mention of it) so while
>> the meaning of [length=NN] isn't exactly obvious, using [l=NN]
>> instead certainly won't make it easier to read.  Does the manual
>> need updating?
>
> Should -fverbose-asm print length (and cost) at all?  They should be
> printed for -dp (which is for debugging the *compiler*), but are they
> very useful for -fverbose-asm (which is primarily for debugging the
> *user program*)?

I don't have the answers to these questions.  What I can say
is that using one letter abbreviations for short words is not
going to make it more readable, on the contrary.  len= would
be okay.

Martin