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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I was thinking that getFixedByteSize could assert that version and address size are non-zero, whenever it was about to use the Params. Then getFixedSizeForAbbrev
could pre-emptively return None for those forms, and default to getFixedByteSize for the rest. Because getFixedSizeForAbbrev only passes along "safe" forms, the assertions won't be triggered.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Knowledge about which forms depend on which parameters should be encapsulated in DWARFFormValue. I would not want to recode the abbreviation-table
scanner to know which forms didn't depend on the Params.<o:p></o:p></span></a></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> David Blaikie [mailto:dblaikie@gmail.com]
<br>
<b>Sent:</b> Friday, June 23, 2017 5:27 PM<br>
<b>To:</b> Robinson, Paul; reviews+D34570+public+9d5e31ef9b3178e4@reviews.llvm.org; aprantl@apple.com<br>
<b>Cc:</b> clayborg@gmail.com; hiraditya@msn.com; llvm-commits@lists.llvm.org<br>
<b>Subject:</b> Re: [PATCH] D34570: [DWARF] NFC: Collect info needed by DWARFFormValue into a helper<o:p></o:p></span></p>
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<p class="MsoNormal">On Fri, Jun 23, 2017 at 5:12 PM Robinson, Paul <<a href="mailto:paul.robinson@sony.com">paul.robinson@sony.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">================<br>
Comment at: llvm/lib/DebugInfo/DWARF/DWARFFormValue.cpp:64<br>
+DWARFFormValue::getFixedByteSize(dwarf::Form Form,<br>
+ const DWARFFormParams *Params) {<br>
switch (Form) {<br>
----------------<br>
dblaikie wrote:<br>
> Should this be optional? The only place that doesn't pass it looks to be DWARFAbbreviationDeclaration::extract - is that usage correct? Does the abbrev table implicit_const not support the extra features? Should there be some error path/check for any forms
that would require the params?<br>
There is a use-case for scanning the abbreviations table to determine which ones are fixed-size in all cases. And the abbreviations table can be shared by units/line-tables with different formats/versions. This was an important point for @clayborg and LLDB,
I think.<br>
So yes, I think it should remain optional. We can change our minds later if I'm wrong.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Still might be worth moving the optionality to that one use case & adding some comments about why it's probably valid there so it doesn't get accidentally propagated to other users.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">So we would have something like:</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> Optional<uint8_t> getFixedByteSize(dwarf::Form Form, const DWARFFormParams &Params);</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> Optional<uint8_t> getFixedByteSizeForAbbrev(dwarf::Form Form);</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">with commentary reinforcing the special case. I can do that.</span><o:p></o:p></p>
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<p class="MsoNormal"><br>
I was thinking abbrev call site could just call: getFixedByteSize(Form, DWARFFormParams()); <br>
<br>
But sure, a separate function that does that might be good. Dunno.<br>
<br>
It'd be good if in some way this was checked somehow to ensure that the forms used by callers not giving DWARFFormParams don't need those properties. I was figuring some assertions at the callsite (but if it has a separate function, the assertions could go
in that function)<br>
<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt"><a href="https://reviews.llvm.org/D34570" target="_blank">https://reviews.llvm.org/D34570</a><o:p></o:p></p>
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