Made a tiny bit of progress today.

On a bigger machine, I was able to profile the giant unit tests module. It
has one top-level for/template that iterates over the 5 scalar types, and a
bunch of smaller ones inside that cover the multitude of operations for
each of the 4 fixed vector lengths.

profiling (lib "glm/vector/tests.rkt")
> Initial code size: 5039
> Final code size  : 1019095
>

The good news is, I'm seeing around 200x compression. I mean, who wouldn't
mind getting completely DRY source for as little as 1/250th the effort?
(Assuming, of course, that programming time is proportional to program size
in bytes.)

The bad news is, compilation takes around 40 seconds on a modern desktop
with plenty of CPU and RAM. From the rest of the profiling output, it looks
like phase-0 for/template is responsible for about 12.5% of the total size,
but phase-1 for/list contributes 57.2% and phase-0 check contributes 48.4%.

I'm not sure how to interpret these numbers yet. On one hand, for/template
is essentially a for/list loop unroller, so the stats could just mean it
did its job. On the other hand, I don't know how much of that 57.2% is
merely the cost of doing business in Racket.

When I comment out everything but the first two tests, I see this:

Initial code size: 243
> Final code size  : 21725
>

That's a mere 89x compression, which is OK because the first two tests are
relatively simple, with phase-0 for/template accounting for 58.5% of the
total size, phase-1 for/list contributing 23.2%, and no phase-0 check.

It's starting to look like there isn't much I can do to bring down the
total size. But what about total compile time?

When I manually unroll the for/template forms, the profiler gives:

Initial code size: 1509
> Final code size  : 21725
>

The identical final size is interesting -- it suggests the original output
sizes are what they would be if templates weren't used.

This version takes, on average, 1.883 seconds to compile. The for/template
version takes 2.499 seconds, and an empty test suite takes 1.743 seconds.
Subtracting out the control time, it took 0.612 seconds more, or 5.4x
longer, to compile a fairly simple module with for/template than without.

Is the extra cost acceptable? I'm guessing that's highly context dependent.
In this case, adding half a second to compile one module wouldn't
inconvenience me terribly, but it doesn't take much imagination to find a
situation where it would, and I have no idea how any of these numbers will
scale.

Eric


On Sat, Mar 14, 2020 at 3:28 PM Eric Griffis <ded...@gmail.com> wrote:

> Alright, I re-discovered Ryan Culpepper's talk, "The Cost of Sugar," from
> the RacketCon 2018 video stream (https://youtu.be/CLjXhr_TgP8?t=5908) and
> made some progress by following along.
>
> Here are the .zo files larger than 100K:
>
> 993K ./vector/compiled/tests_rkt.zo
> 830K ./scribblings/compiled/glm_scrbl.zo
> 328K ./vector/compiled/relational_rkt.zo
> 295K ./vec4/compiled/bool_rkt.zo
> 291K ./vec4/compiled/int_rkt.zo
> 290K ./vec4/compiled/uint_rkt.zo
> 290K ./vec4/compiled/double_rkt.zo
> 289K ./vec4/compiled/float_rkt.zo
> 280K ./vec3/compiled/bool_rkt.zo
> 276K ./vec3/compiled/int_rkt.zo
> 275K ./vec3/compiled/uint_rkt.zo
> 275K ./vec3/compiled/double_rkt.zo
> 274K ./vec3/compiled/float_rkt.zo
> 262K ./vec2/compiled/bool_rkt.zo
> 258K ./vec2/compiled/uint_rkt.zo
> 258K ./vec2/compiled/int_rkt.zo
> 258K ./vec2/compiled/double_rkt.zo
> 257K ./vec2/compiled/float_rkt.zo
> 213K ./vec1/compiled/bool_rkt.zo
> 210K ./vec1/compiled/uint_rkt.zo
> 210K ./vec1/compiled/int_rkt.zo
> 210K ./vec1/compiled/double_rkt.zo
> 209K ./vec1/compiled/float_rkt.zo
> 102K ./compiled/main_rkt.zo
> 101K ./compiled/vector_rkt.zo
>
> I'm pretty sure that's a lot of big files. It's for a port of GLM, a
> graphics math library that implements (among other things) fixed-length
> vectors of up to 4 components over 5 distinct scalar types, for a total of
> 20 distinct type-length combinations with many small variations in their
> APIs and implementations.
>
> The variations I'm targeting either require a macro or exacerbate
> developer- or run-time overhead when functions are introduced. For example,
> the base component accessors for a four-component vector of doubles are:
>
>   dvec4-x
>   dvec4-y
>   dvec4-z
>   dvec4-w
>
> Each of the "xyzw" components has two aliases -- one from "rgba" and
> another from "stpq". Each accessor also has a corresponding mutator, e.g.,
> dvec4-g and set-dvec4-g!.
>
> For another example, whereas adding two dvec4's sums four components,
>
>   (dvec4
>    (fl+ (dvec4-x v1) (dvec4-x v2))
>    (fl+ (dvec4-x v1) (dvec4-x v2))
>    (fl+ (dvec4-x v1) (dvec4-x v2))
>    (fl+ (dvec4-x v1) (dvec4-x v2)))
>
> the same operation on dvec2's sums only the first two components.
>
> Furthermore, the sheer volume of the target code base makes writing
> everything out by hand a mind-numbing exercise in frustration, and that's
> when looking at a mere 20% of the pile. It's going to get much worse very
> quickly. To add fixed-length matrices up to shape 4x4 over the same scalar
> types, I'm looking at 16x5 = 80 more distinct type-shape combinations!
>
> Getting back to the .zo files, I had no luck running "raco macro-profiler"
> on the top end of the list. It appears to diverge. My dev laptop probably
> doesn't have enough RAM, so I'll have to try again on a bigger machine.
>
> Here's an excerpt from a file on the bottom end:
>
> [eric@walden racket-glm]$ raco macro-profiler glm/vec4/double
> profiling (lib "glm/vec4/double.rkt")
> Initial code size: 87
> Final code size  : 86531
> ========================================
> Phase 0
> the-template (defined as the-template.1 in glm/vector/template)
>   total: 31536, mean: 31536
>   direct: 2054, mean: 2054, count: 1, stddev: 0
> define-dvec4-unop (defined in "this module")
>   total: 7300, mean: 730
>   direct: 7480, mean: 748, count: 10, stddev: 0
> define/contract (defined in racket/contract/region)
>   total: 6666, mean: 44
>   direct: 3572, mean: 23, count: 153, stddev: 1.48
> define-dvec4-binop (defined in "this module")
>   total: 6200, mean: 620
>   direct: 6380, mean: 638, count: 10, stddev: 0
> ...
>
> Phase 1
> for/list (defined in racket/private/for)
>   total: 6558, mean: 273
>   direct: 2274, mean: 95, count: 24, stddev: 14.94
> for/fold/derived/final (defined in racket/private/for)
>   total: 4332, mean: 180
>   direct: 336, mean: 14, count: 24, stddev: 0
> for/fold/derived (defined in racket/private/for)
>   total: 4284, mean: 178
>   direct: 240, mean: 10, count: 24, stddev: 0
> for/foldX/derived (defined in racket/private/for)
>   total: 3996, mean: 24
>   direct: 3164, mean: 19, count: 170, stddev: 48.16
>
> Wow, does that look like nearly 1000x compression? Three orders of
> magnitude seems right, given what I know about how these macros interact.
>
> The "the-template" macro is defined inside a module generated by my custom
> #%module-begin. It defines 4 type-agnostic, fixed-length module templates
> (e.g., glm/vec4/template), which are instantiated once for each of the 5
> scalar types. Those fixed-length module templates are based, in turn, on
> another module template (glm/vector/template) that takes a length argument
> and uses the other profiled macros (define-dvec4-unop, define/contract,
> define-dvec4-binop) to create 20 component-wise operations per instance.
> All together, that should inflate the size of the output to somewhere near
> the middle of the interval 4x20x5x[1,4], which is 1000.
>
> At phase 1, the comprehension forms are busy churning out component
> aliases and unrolling component-wise operations at "compile" time. I'm
> reluctant to anti-inline these because they keep the written code small and
> the generated code fast.
>
> I guess the next step is to anti-inlinedefine-dvec4-unop and
> define-dvec4-binop, maybe eliminate some define/contract's, and re-profile.
>
> Eric
>
>
> On Friday, March 13, 2020 at 6:20:47 PM UTC-7, Eric Griffis wrote:
>>
>> Hello,
>>
>> I've got a package that generates (i.e., expands into) a ridiculous
>> amount of Racket code. I'd like to generate an unbelievable amount of
>> code, but things have already slowed down a lot.
>>
>> At this point, I'm generating 20% of a massive code base and it takes
>> 4 minutes to compile (i.e., raco make) it all. If those numbers scale
>> linearly, I'm looking at 20 minutes to generate and compile the full
>> code base. Realistically, that's an optimistic lower bound.
>>
>> How might I go about profiling something that does most of its work at
>> expansion time?
>>
>> Should I be concerned about knocking over or clogging the package
>> repository when checking in highly "compressed" meta-programs that
>> unfurl at compile time?
>>
>> Thanks!
>>
>> Eric
>>
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