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<p>Hi James:</p>
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<p>Good point. I am considering the following case - </p>
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<pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="color: rgb(0, 102, 153); font-weight: bold; font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;">struct</span><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"> test_struct {</span></pre>
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<pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"> </span><span style="color: rgb(0, 102, 153); font-weight: bold; font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;">int</span><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"> a;</span></pre>
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<pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"> int32x4_t b;</span></pre>
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<pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;">};</span></pre>
<pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"><br></span></pre>
<pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;">clang will currently give it 12 bytes of padding, even though it should have been 4 bytes according to AAPCS.</span></pre>
<pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"><table cellspacing="0" cellpadding="0" border="0" width="100%" style="font-family: Arial, sans-serif; font-size: 1em; line-height: 1.4em !important;"><tbody><tr id="syntaxplugin_code_and_gutter"><td style="padding: 0em; vertical-align: top; line-height: 1.4em !important;"><pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"><br></span></pre><pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;">*** Dumping AST Record Layout</span></pre></td></tr><tr id="syntaxplugin_code_and_gutter"><td style="padding: 0em; vertical-align: top; line-height: 1.4em !important;"><pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"> 0 | struct test_struct</span></pre></td></tr><tr id="syntaxplugin_code_and_gutter"><td style="padding: 0em; vertical-align: top; line-height: 1.4em !important;"><pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"> 0 | int a</span></pre></td></tr><tr id="syntaxplugin_code_and_gutter"><td style="padding: 0em; vertical-align: top; line-height: 1.4em !important;"><pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"> 16 | int32x4_t b</span></pre></td></tr><tr id="syntaxplugin_code_and_gutter"><td style="padding: 0em; vertical-align: top; line-height: 1.4em !important;"><pre style="margin: 0px 10px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;"><span style="font-family: Consolas, "Bitstream Vera Sans Mono", "Courier New", Courier, monospace !important;"> | [sizeof=32, align=16]</span></pre></td></tr></tbody></table>Best Regards </span></pre>
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<pre style="margin: 0px 10px; padding: 0px; counter-reset: lines 0; font-size: 1em; width: auto;">Javed </pre>
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<p></p>
p.s. James, for some reason, you comment does not appear in the phabricator.</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> James Molloy <james@jamesmolloy.co.uk><br>
<b>Sent:</b> 15 May 2017 18:49<br>
<b>To:</b> reviews+D33205+public+7fad182a923fbe49@reviews.llvm.org; Javed Absar via Phabricator; Javed Absar; diana.picus@linaro.org; renato.golin@linaro.org<br>
<b>Cc:</b> junbuml@codeaurora.org; llvm-commits@lists.llvm.org; kanheim@a-bix.com<br>
<b>Subject:</b> Re: [PATCH] D33205: ARM] Fix Neon vector type alignment to 64-bit</font>
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<div>Hi Javed,<br>
<br>
Why reduce the preferred alignment from 128? Natural vector alignment means we can more often use the :128 hints on loads and stores.
<br>
<br>
What's the rationale here?<br>
<br>
James<br>
<div class="gmail_quote">
<div dir="ltr">On Mon, 15 May 2017 at 18:10, Javed Absar via Phabricator via llvm-commits <<a href="mailto:llvm-commits@lists.llvm.org">llvm-commits@lists.llvm.org</a>> wrote:<br>
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<blockquote class="gmail_quote" style="margin:0 0 0 .8ex; border-left:1px #ccc solid; padding-left:1ex">
javed.absar created this revision.<br>
Herald added subscribers: srhines, aemerson.<br>
<br>
The maximum alignment for ARM NEON data types should be 64-bits as specified in ARM procedure call standard document Sec. A.2 Notes [1]. This patch fixes it from its current larger natural default values.<br>
<br>
[1] <a href="http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042f/IHI0042F_aapcs.pdf" rel="noreferrer" target="_blank">
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042f/IHI0042F_aapcs.pdf</a><br>
<br>
<br>
<a href="https://reviews.llvm.org/D33205" rel="noreferrer" target="_blank">https://reviews.llvm.org/D33205</a><br>
<br>
Files:<br>
lib/Basic/Targets.cpp<br>
test/CodeGen/arm-abi-vector.c<br>
test/CodeGen/arm-neon-misc.c<br>
test/CodeGen/arm-swiftcall.c<br>
test/CodeGen/armv7k-abi.c<br>
<br>
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