<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Nov 5, 2014, at 6:15 PM, Philip Reames <<a href="mailto:listmail@philipreames.com" class="">listmail@philipreames.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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<div class="moz-cite-prefix">On 11/05/2014 06:00 PM, Andrew Trick
wrote:<br class="">
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<div class="">On Nov 5, 2014, at 5:28 PM, Philip Reames <<a moz-do-not-send="true" href="mailto:listmail@philipreames.com" class="">listmail@philipreames.com</a>>
wrote:</div>
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<div class=""><span style="font-family: Helvetica; font-size:
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<span style="font-family: Helvetica; font-size: 12px;
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none; display: inline !important;" class="">Comment at:
include/llvm/CodeGen/MachineInstr.h:91</span><br style="font-family: Helvetica; font-size: 12px;
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none; display: inline !important;" class="">@@ -90,3 +90,3
@@</span><br style="font-family: Helvetica; font-size:
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<br style="font-family: Helvetica; font-size: 12px;
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<span style="font-family: Helvetica; font-size: 12px;
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none; display: inline !important;" class="">- uint8_t
NumMemRefs; // Information on memory
references.</span><br style="font-family: Helvetica;
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none; display: inline !important;" class="">+ uint16_t
NumMemRefs; // Information on memory
references.</span><br style="font-family: Helvetica;
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<span style="font-family: Helvetica; font-size: 12px;
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none; display: inline !important;" class=""> mmo_iterator
MemRefs;</span><br style="font-family: Helvetica;
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<span style="font-family: Helvetica; font-size: 12px;
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none; display: inline !important;" class="">----------------</span><br style="font-family: Helvetica; font-size: 12px;
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<span style="font-family: Helvetica; font-size: 12px;
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none; display: inline !important;" class="">ributzka
wrote:</span><br style="font-family: Helvetica; font-size:
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<blockquote type="cite" style="font-family: Helvetica;
font-size: 12px; font-style: normal; font-variant: normal;
font-weight: normal; letter-spacing: normal; line-height:
normal; orphans: auto; text-align: start; text-indent:
0px; text-transform: none; white-space: normal; widows:
auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Are you really hitting the limitations of uint8_t
for mem references? Changing this by one byte increases
the overall size of a MachineInstr from 64 bytes to 72
bytes (due to padding).<br class="">
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<span style="font-family: Helvetica; font-size: 12px;
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normal; letter-spacing: normal; line-height: normal;
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none; display: inline !important;" class="">We were at one
point. I'm not sure we still are. I'm fine removing this
in the change which initially gets upstreamed and
revisiting this separately. </span></div>
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<div class="">Good, thanks. A lot of careful engineering went into
packing MachineInstr into 64 bytes in order to squeeze compile
time out of backend passes. And we still get complaints that
machine code is too slow to generate. If we need more MemRefs,
we’ll have to come up with another way to get them.</div>
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I'm happy to separate this, but looking at the surrounding fields,
it looks like there are a few bits to spare. The CommentFlags and
Flags enums only need a combined 4 bits. They're currently
consuming 16 bits. And that's without even playing any tricks with
tagged pointers. :)<br class=""></div></div></blockquote><div><br class=""></div><div>Yeah, stealing bits is fine. That’s what I meant by “come up with another way [to get MemRefs]”.</div><div class=""><br class=""></div><blockquote type="cite" class=""><div class=""><div bgcolor="#FFFFFF" text="#000000" class="">
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Restructuring this would definitely be a different change set
though.<br class=""></div></div></blockquote><div><br class=""></div>Definitely. Thanks.</div><div><br class=""><blockquote type="cite" class=""><div class=""><div bgcolor="#FFFFFF" text="#000000" class="">
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We might even be able to squeeze another word out of the structure,
but I don't know enough about which fields are hot to be sure. :)<br class="">
</div></div></blockquote><br class=""></div><div><br class=""></div><div>-Andy</div><br class=""></body></html>