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current/compiler/js-calc.xsl (compile-calc-value): Drastically reduce matching complexity 

This takes a bunch of individual templates and combines them into one, while
also utilizing the already-available symbol table map in place of using an
XPath on `preproc:symtable`.

The results are much more drastic than I was expecting.

I was exploring this because one of our largest packages was spending most
of its time (~5m) in fragment compilation, which was a surprise to
me.  Prior work I did for runtime optimizations led to optimizations in its
parent `js.xsl`, but not in `js-calc.xsl`, which has largely been untouched
since it was originally written for XSLT 1 over 10 years ago.

Because it was originally written for XLST 1, it does not take advantage of
maps, tunneling variables, or various other options.  Further, it was
written in a naive way that was convenient (and clear) at the time, and
wholly acceptable for smaller inputs.  But, as is the case with
quadratic-time systems, there are severe growing pains.

This change reduced the package compilation time from 5-6m down to 1m15s,
and this was just the first attempt at optimizing it.  I should have taken a
look at this long ago, but my efforts were focused on TAMER, and I didn't
want to divert that focus.  That was a mistake.  Symptoms of this problem
were already prevalent ~10 months ago, when the package was taking 3 minutes
to compile (so the time has since doubled).

This also eliminates `@magic`, which has not been used for a long time (it
used to be used for a "constant" that held the current date/time; such a
value is now passed into the system like any other input).

After making this change, the resulting packages are byte-for-byte
identical.

I also noticed, though I haven't tried to measure it, that there seem to be
fewer multi-core spikes; this is possibly related to Saxon not trying to
evaluate expensive `template/match` expressions concurrently anymore.  If
true, this will also help with resource contention for parallel builds.

DEV-15095
main
Mike Gerwitz 2023-10-12 10:29:14 -04:00
parent b2a996c1df
commit b7372fe7cd
1 changed files with 105 additions and 175 deletions
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170
src/current/compiler/js-calc.xsl
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@ -502,149 +502,77 @@
<!--
Generate JS representing the value of a function argument
Generate code for a `c:value-of`.
This will match whenever value-of is used on a name that matches any function
parameter.
XXX: We want to remain decoupled from lv if possible.
@return generated JS representing argument value or 0
This combines what was previously a number of individual templates into a
large `choose`; this is important to avoid duplicate symbol table lookups
and expensive XPaths as Saxon attempts to determine which template
matches.
-->
<template mode="compile-calc-value"
match="c:*[@name=ancestor::lv:function/lv:param/@name]">
match="*" priority="9">
<param name="symtable-map" as="map(*)" tunnel="yes" />
<!-- use the argument passed to the function -->
<apply-templates select="." mode="compile-calc-index">
<with-param name="value" select="@name" />
</apply-templates>
</template>
<variable name="value-sym" as="element( preproc:sym )?"
select="$symtable-map( @name )" />
<variable name="name" as="xs:string" select="@name" />
<!--
Using value from let expressions
-->
<template mode="compile-calc-value"
match="c:*[ @name=ancestor::c:let/c:values/c:value/@name ]">
<!-- compile the value with the index (if any) -->
<apply-templates select="." mode="compile-calc-index">
<with-param name="value" select="@name" />
</apply-templates>
</template>
<!--
Generate JS representing the value of a global constant
Since constants are intended only to prevent magic values during development
(and are not required at runtime), the value of the constant will be placed
directly into the compiled code. However, we will *not* do this if the
constant is a set, since its index may be determined at runtime.
Note that "magic" constants' values are not inlined.
@return quoted constant value
-->
<template mode="compile-calc-value"
match="
c:*[
@name=root(.)/preproc:symtable/preproc:sym[
@type='const'
and @dim='0'
]/@name
]
">
<variable name="name" select="@name" />
<variable name="sym"
select="root(.)/preproc:symtable/preproc:sym[ @name=$name ]" />
<!-- it is expected that validations prior to compiling will prevent JS
injection here -->
<choose>
<!-- "magic" constants should not have their values inlined -->
<when test="$sym/@magic='true'">
<text>C['</text>
<value-of select="@name" />
<text>']</text>
<!-- global scalar constant (@value is only defined when @dim is 0) -->
<when test="$value-sym[ @type = 'const' and @dim = '0' ]">
<variable name="value" as="xs:string"
select="$value-sym/@value" />
<!-- note: this used to check for @magic, which has long since been
removed -->
<sequence select="$value" />
</when>
<!-- @value should be defined when @dim=0 -->
<otherwise>
<value-of select="$sym/@value" />
</otherwise>
</choose>
</template>
<!--
Generates JS representing the value of a constant as part of a set
Since the index of constant sets can be determined at runtime, we need to
store all possible values. As such, we shouldn't repeat ourselves by inlining
all possible values; instead, we'll reference a pre-generated set of values
for the particular constant.
@return generated code representing value of a variable, or 0 if undefined
-->
<template mode="compile-calc-value"
match="
c:*[
@name=root(.)/preproc:symtable/preproc:sym[
@type='const'
and not( @dim='0' )
]/@name
]
">
<!-- non-scalar constants are large and are stored statically for
reference rather than being inlined -->
<when test="$value-sym[ @type = 'const' and not( @dim = '0' ) ]">
<variable name="value">
<text>C['</text>
<value-of select="@name" />
<value-of select="$name" />
<text>']</text>
</variable>
<apply-templates select="." mode="compile-calc-index">
<with-param name="value" select="$value" />
</apply-templates>
</template>
</when>
<!--
Generate JS representing the value of a generated index
@return generated code associated with the value of the generated index
-->
<template mode="compile-calc-value"
match="c:*[ @name = ancestor::c:*[ @of ]/@index ]">
<!-- depending on how the index is generated, it could be a string, so we must
cast it -->
<!-- TODO: is this worth a tunnel instead of `ancestor::`? -->
<!-- generator index -->
<when test="$name = ancestor::c:*[ @of ]/@index">
<!-- TODO: This shouldn't be true anymore; is this cast still needed? -->
<!-- depending on how the index is generated, it could be a string, so
we must cast it -->
<text>+</text>
<value-of select="@name" />
</template>
<value-of select="$name" />
</when>
<!-- function argument -->
<when test="$name = ancestor::lv:function/lv:param/@name">
<!-- use the argument passed to the function -->
<apply-templates select="." mode="compile-calc-index">
<with-param name="value" select="$name" />
</apply-templates>
</when>
<!--
Generates JS representing the value of a variable
<!-- let expression value -->
<when test="$name = ancestor::c:let/c:values/c:value/@name">
<!-- compile the value with the index (if any) -->
<apply-templates select="." mode="compile-calc-index">
<with-param name="value" select="$name" />
</apply-templates>
</when>
If the variable is undefined, the value will be considered to be 0 (this is
especially important for the summation of sets within this implementation).
That is: a value will never be considered undefined.
<otherwise>
<variable name="dim" as="xs:string"
select="$value-sym/@dim" />
@return generated code representing value of a variable, or 0 if undefined
-->
<template match="c:*" mode="compile-calc-value">
<variable name="name" select="@name" />
<variable name="pkg" as="element( lv:package )"
select="root(.)" />
<variable name="dim"
select="$pkg/preproc:symtable/preproc:sym[ @name=$name ]/@dim" />
<!-- retrieve the value, casting to a number (to avoid potentially nasty
string concatenation bugs instead of integer/floating point arithmetic)
as long as we're either not a set, or provide an index for the set -->
<variable name="value">
<text>A['</text>
<value-of select="@name" />
@ -689,6 +617,8 @@
<apply-templates select="." mode="compile-calc-index">
<with-param name="value" select="$value" />
</apply-templates>
</otherwise>
</choose>
</template>