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<div class="moz-cite-prefix">Hi Neil,</div>
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<div class="moz-cite-prefix">we want to make the representation more concise.</div>
<div class="moz-cite-prefix"><br>
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<div class="moz-cite-prefix">One more thing i just realized is that we could use the tuple types to mask optimizations that do not expect them*.<br>
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<div class="moz-cite-prefix">Eg standard fp optimizations could claim that they handle `llvm.fadd` unless there are any parameter tuples on it.</div>
<div class="moz-cite-prefix">Likewise, we can then implement a masked constrainedfp, SIMD fadd optimization pass that handles `llvm.fadd` with `fpenv` and/or `mask`.</div>
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<div class="moz-cite-prefix">*: (this comes on the heels of a second to-be-published RFC on generalizing the pattern match logic in LLVM...)</div>
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<div class="moz-cite-prefix">- Simon<br>
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<div class="moz-cite-prefix">On 2/12/20 11:40 AM, Neil Henning wrote:<br>
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<blockquote type="cite" cite="mid:CALRoqd0z3-2qCYfQMmHxrLNh=pmHM+YZqtp-_K685hiFM6FqcQ@mail.gmail.com">
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<div>Hey Simon,</div>
<div><br>
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<div>It wasn't clear from your RFC: why can't you just have these optional parameter tuples be normal function arguments to the intrinsics?</div>
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<div>Cheers,</div>
<div>-Neil.<br>
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<div dir="ltr" class="gmail_attr">On Wed, Feb 12, 2020 at 9:28 AM Simon Moll via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" moz-do-not-send="true">llvm-dev@lists.llvm.org</a>> wrote:<br>
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<p>Hi,</p>
<p>this is an RFC for optional, named parameter tuples for intrinsics. The proposed syntax is:</p>
<p><tt>%z = call @llvm.some.intrinsic(%a, %b) optional_tuple(%x, %y, %z)</tt></p>
<p>where from the perspective of the call site %x, %y and %z are simply additional parameters.<br>
</p>
<p>Optional parameter tuples would be very useful for constrained fp intrinsics and vector predication. Some examples:</p>
<p><span></span></p>
<pre>; Default fpenv fadd (isomorphic to the fadd instruction)
%z = call double @llvm.fadd(%a, %b)
<span><pre>; Constrained fp add
%x = call double @llvm.fadd(%a, %b) fpenv(metadata !fpround.tonearest, metadata !fpexcept.strict)
</pre></span></pre>
<pre><span><pre>; Constrained fp add with vector predication (<a href="https://reviews.llvm.org/D57504" target="_blank" moz-do-not-send="true">https://reviews.llvm.org/D57504</a>)
%x = call <256 x double> @llvm.fadd(%a, %b) mask(<256 x i1> %mask), evl(i32 %evl), fpenv(metadata !fpround.tozero, metadata !fpexcept.strict)<span></span></pre></span></pre>
<p>For constrained fp and VP, we only require a very restricted form of this. That is:</p>
<p>- Tuples are only allowed on intrinsic function calls.<br>
</p>
<p>- There is a builtin list of allowed tuple types (eg tablegen file).<br>
</p>
<p>- Tuple types are opt in: Intrinsics define a list of permissible tuple types.<br>
</p>
<p>- Tuple parameters have default values when a tuple is absent at a call site. Eg, for `<tt>fpenv</tt>` the default fp environment `<tt>fpenv(fpround.tonearest, fpexcept.ignore)</tt>` is implied in the first example above.<br>
</p>
<p><br>
</p>
<p>Btw, different to operand bundles, optional parameter tuples are much more restricted and do not imply side effects of any kind. We might want to re-use the OpBundle logic for this though.<br>
</p>
<p>There are probably more use cases for this and i'd like to hear about them.<br>
</p>
<p>Looking forward to your feedback</p>
<p>- Simon<br>
</p>
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