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List:       gcc-patches
Subject:    Re: [PATCH] final: Improve output for -dp and -fverbose-asm
From:       Martin Sebor <msebor () gmail ! com>
Date:       2017-11-30 22:54:30
Message-ID: 53eb6162-a9c9-ed2f-c3dc-85bc38bf29fd () gmail ! com
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On 11/30/2017 10:07 AM, Segher Boessenkool wrote:
> On Thu, Nov 30, 2017 at 09:54:26AM -0700, Martin Sebor wrote:
>>> It is neither line length nor amt of info that makes the second one
>>> way better readable.
>>
>> The justification certainly makes it easier to read.  But
>> the abbreviations make it harder to interpret.  [c=4 l=4]
>> makes no sense to anyone not already familiar with what
>> it means.
>>
>> There's nothing wrong with using mnemonics as long as they're
>> well established and commonly understood.  Absent that, they
>> should be explained in some accessible document.
>>
>> Not everyone who reads the verbose assembly is familiar with
>> GCC internals.  Users read it to help debug problems in their
>> code.  They shouldn't have to also study GCC source code to
>> understand what the contents mean.
>
> This is the -dp output, I hardly ever use -fverbose-asm, it has been
> unreadable for ten years or so.
>
> -fverbose-asm looks like this:
> ===
> .L.yk:
>  # 81288.c:4:   unsigned int *un = (f3 != 0) ? &t4 : 0;
>         cmpdi 0,4,0      # tmp130, f3
>         beq 0,.L2        #
>  # 81288.c:6:   *un ^= t4;
>         srdi 9,3,32      #, tmp131, t4
>         xor 9,9,3        #, tmp132, tmp131, t4
>  # 81288.c:7:   if (*un == t4)
>         rldicl 9,9,0,32  # tmp133, tmp132
>  # 81288.c:7:   if (*un == t4)
>         cmpd 7,9,3       # t4, tmp134, tmp133
>         beq 7,.L7        #
> .L5:
>  # 81288.c:11: }
>         mr 3,4   #, <retval>
>         blr
> .L2:
>  # 81288.c:6:   *un ^= t4;
>         lwz 9,0(4)       # MEM[(unsigned int *)0B], _13
>         trap
> .L7:
>  # 81288.c:8:     f3 = !!t4;
>         addic 4,9,-1     # tmp139, tmp133
>         subfe 4,4,9      # <retval>, tmp139, tmp133
>         b .L5    #
> ===
>
> If we're okay with outputting that kind of stuff to *users*, then how
> bad is [c=8 l=4] for GCC developers?  Heh.

I don't know if the above is okay or not.  What I do know is
that [l=4] is not an improvement over [length = 4].

But I think there are ways to improve the readability while
at the same time making the output more compact.  I mentioned
documenting the labels (whatever they may be) in the manual
as one possibility.  Another idea is to print a brief legend
at the bottom of the file explaining what l= stands for.  Yet
another is to print a header at the top of every function with
a label for each column (like in the top command), and then
document what each column means in the manual by referring
to the column headers.  I'm sure there are others.

Martin
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