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<font size="4"><font face="monospace">I'd like to be a little more
aggressive on that: if generation is not disabled, then any
stack map sent downstream is dropped on the floor, and either
the original stackmap reused, or a new one generated.
Generating stack maps is definitely an advanced, error-prone
feature; users should have to turn it on. <br>
<br>
Given this, though, I think we can drop the PROCESS_STACK_MAP
attribute, and always send it downstream, as this costs us
almost nothing and the user can ignore it. <br>
<br>
We should definitely not generate Code attributes with more than
one stack map attribute in them. <br>
</font></font><br>
<div class="moz-cite-prefix">On 8/17/2022 12:02 PM, Adam Sotona
wrote:<br>
</div>
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<p class="MsoNormal"><span style="font-size:11.0pt" lang="EN-US">Yes,
user can send the stack maps to the builder anytime and it
will disable generation for the actual method.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt" lang="EN-US">However
user has to explicitly construct the attribute:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt" lang="EN-US">cob.with(StackMapTableAttribute.of(List.of(StackMapFrameInfo.of(myLabel,
locals, stack), …));<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt" lang="EN-US">Generation
switch works independently, so user can keep the generation
on for some methods and explicitly specify/transform
StackMapTableAttribute for other methods of the same class.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<div style="border:none;border-top:solid #B5C4DF
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<p class="MsoNormal" style="mso-margin-top-alt:0cm;margin-right:0cm;margin-bottom:12.0pt;margin-left:36.0pt"><b><span style="color:black">From: </span></b><span style="color:black">Brian Goetz
<a class="moz-txt-link-rfc2396E" href="mailto:brian.goetz@oracle.com"><brian.goetz@oracle.com></a><br>
<b>Date: </b>Wednesday, 17 August 2022 17:53<br>
<b>To: </b>Adam Sotona <a class="moz-txt-link-rfc2396E" href="mailto:adam.sotona@oracle.com"><adam.sotona@oracle.com></a>,
<a class="moz-txt-link-abbreviated" href="mailto:classfile-api-dev@openjdk.org">classfile-api-dev@openjdk.org</a>
<a class="moz-txt-link-rfc2396E" href="mailto:classfile-api-dev@openjdk.org"><classfile-api-dev@openjdk.org></a><br>
<b>Subject: </b>Re: RFR: Classfile API stack maps
processing</span><span style="color:black;mso-fareast-language:EN-GB"><o:p></o:p></span></p>
</div>
<p class="MsoNormal" style="mso-margin-top-alt:0cm;margin-right:0cm;margin-bottom:12.0pt;margin-left:36.0pt"><span style="font-size:13.5pt;font-family:"Courier New"">See
the RFR, I think I found a place where we might end up
putting TWO stack map attributes into the builder.
<br>
<br>
With this patch, I believe the treatment of stack maps is
intended to be:<br>
<br>
if (generation not disabled) { <br>
try to reuse original stackmap, if transforming and
code array/exception table is unchanged<br>
otherwise generate stack map<br>
}<br>
else { <br>
if a stack map has been sent to the builder, put that
in the class file<br>
}<br>
<br>
I am not sure this is the effect, though; since the user can
send stack maps down the pipe and they are stored as
attributes regardless of options, I think these may be
written to the classfile even if we are in generation mode.
<br>
<br>
</span><span style="font-size:11.0pt"><o:p></o:p></span></p>
<div>
<p class="MsoNormal" style="margin-left:36.0pt">On 8/17/2022
11:45 AM, Adam Sotona wrote:<o:p></o:p></p>
</div>
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<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Hi,</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">I would like to ask
for review of proposed change in the Classfile API stack
maps processing.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Primary motivation
is to better align stack maps processing with the
Classfile API and to allow manual constructions and
transformations of stack maps.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Pull request for
review is here:
<a href="https://github.com/openjdk/jdk-sandbox/pull/32" moz-do-not-send="true" class="moz-txt-link-freetext">https://github.com/openjdk/jdk-sandbox/pull/32</a></span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">And it includes
following changes:</span><o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0
level1 lfo3">
<!--[if !supportLists]--><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]--><span style="font-size:11.0pt" lang="EN-US">New boolean
Classfile.Option::processStackMaps with default to false
has been added</span><o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0
level1 lfo3">
<!--[if !supportLists]--><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]--><span style="font-size:11.0pt">StackMapTableAttribute</span><span style="font-size:11.0pt" lang="EN-US"> become a
CodeElement processed when the above option is explicitly
enabled by user</span><o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0
level1 lfo3">
<!--[if !supportLists]--><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]--><span style="font-size:11.0pt">StackMapTableAttribute</span><span style="font-size:11.0pt" lang="EN-US">, StackMapFrameInfo,
VerificationTypeInfo, SimpleVerificationTypeInfo,
ObjectVerificationTypeInfo and
UninitializedVerificationTypeInfo have been simplified,
refactored to use Labels instead of offsets and equipped
with relevant static factory methods</span><o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0
level1 lfo3">
<!--[if !supportLists]--><span style="mso-list:Ignore">4.<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]--><span style="font-size:11.0pt" lang="EN-US">Redundant content of the StackMapFrameInfo
and its sub-classes reflecting compressed frame forms have
been removed</span><o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0
level1 lfo3">
<!--[if !supportLists]--><span style="mso-list:Ignore">5.<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]--><span style="font-size:11.0pt" lang="EN-US">UnboundStackMapTableAttribute with proper
serialization has been implemented</span><o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l0
level1 lfo3">
<!--[if !supportLists]--><span style="mso-list:Ignore">6.<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]--><span style="font-size:11.0pt" lang="EN-US">CorpusTest with RebuildingTransformations has
been extended to process stack maps using the new API</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">New stack maps
processing option affects inflation of stack maps and
appearance of StackMapTableAttribute in the CodeElement
stream.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Enabled stack maps
processing inflates and decompresses
StackMapTableAttribute with translated offsets to Labels
and pass it to CodeTransformation(s).</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">User can
individually filter StackMapTableAttribute out or
transform it manually when explicitly enabled stack maps
processing.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">User-provided or
transformed StackMapTableAttribute passed to CodeBuilder
overrides stack maps generation process for the actual
method.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Compressed source
form of the parsed stack map frame can be identified from
StackMapFrameInfo::tag</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">All new created
StackMapFrameInfos always represent full frames with
complete list of locals and stack.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Compression of
StackMapTableAttribute frames is contextual operation and
it is applied at the writing phase.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Any NO-OP
transformation of inflated and decompressed
StackMapTableAttribute may result in a different
compressed form.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Performance boost
tricks by-passing stack maps generation for unchanged
methods are unaffected by this enhancement.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Thanks for your
comments,</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US">Adam</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt" lang="EN-US"> </span><o:p></o:p></p>
</blockquote>
<p class="MsoNormal" style="margin-left:36.0pt"><span style="font-size:11.0pt;mso-fareast-language:EN-GB"><o:p> </o:p></span></p>
</div>
</blockquote>
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