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Right, If OpenCL mode compilation flag is removed from the example that Alexey has given, the compilation fails!<br>
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FYI, I just came across this old bug discussing similar issue:</div>
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<a href="https://bugs.llvm.org/show_bug.cgi?id=33103" id="LPlnk309398">https://bugs.llvm.org/show_bug.cgi?id=33103</a><br>
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<div id="divRplyFwdMsg" dir="ltr"><font style="font-size:11pt" face="Calibri, sans-serif" color="#000000"><b>From:</b> Bader, Alexey <alexey.bader@intel.com><br>
<b>Sent:</b> 19 May 2020 20:31<br>
<b>To:</b> Finkel, Hal J. <hfinkel@anl.gov>; Anastasia Stulova <Anastasia.Stulova@arm.com>; Keane, Erich <erich.keane@intel.com>; Min-Yih Hsu <minyihh@uci.edu>; cfe-dev (cfe-dev@lists.llvm.org) <cfe-dev@lists.llvm.org><br>
<b>Cc:</b> nd <nd@arm.com><br>
<b>Subject:</b> RE: [cfe-dev] [RFC] Ternary operator with vector type predicate</font>
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<span style="" lang="EN-US">I never used this extensions in non-OpenCL mode, so I can’t predict what is the impact of the proposed changes.</span></p>
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<span style="" lang="EN-US"> </span></p>
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<span style="" lang="EN-US">I just note that code snippet from the original email works in OpenCL mode as described in RFC with one very minor note:</span></p>
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<span style="color:#666666" lang="EN-US">I’m proposing to support vector type values as predicates in the ternary operator:
<b>If the predicate value has vector type, each of its element would be converted to bool before being used to select corresponding elements from the second or third operands.</b> Note that this is exactly what GCC is doing right now [1] in their vector extensions.</span><span lang="EN-US"></span></li></ul>
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<span style="" lang="EN-US"> </span></p>
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<span style="" lang="EN-US">In OpenCL mode the comparison operator returns bitmask to enable bitwise operations (https://godbolt.org/z/F6ynx6):</span></p>
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<span style="" lang="EN-US"> </span></p>
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<span style="font-family:"Consolas,",serif; color:black" lang="EN-US">float4 foo(float4 a, float4 b, int4 *c) {</span></p>
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<span style="font-family:"Consolas,",serif; color:black" lang="EN-US"> <span style="background:yellow">int4 x = {</span></span><span style="font-family:"Consolas,",serif; color:#098658; background:yellow" lang="EN-US">1</span><span style="font-family:"Consolas,",serif; color:black; background:yellow" lang="EN-US">, </span><span style="font-family:"Consolas,",serif; color:#098658; background:yellow" lang="EN-US">2</span><span style="font-family:"Consolas,",serif; color:black; background:yellow" lang="EN-US">, </span><span style="font-family:"Consolas,",serif; color:#098658; background:yellow" lang="EN-US">3</span><span style="font-family:"Consolas,",serif; color:black; background:yellow" lang="EN-US">, </span><span style="font-family:"Consolas,",serif; color:#098658; background:yellow" lang="EN-US">4</span><span style="font-family:"Consolas,",serif; color:black; background:yellow" lang="EN-US">};</span></p>
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<span style="font-family:"Consolas,",serif; color:black; background:yellow" lang="EN-US"> *c = (a < b) & x;</span><span style="font-family:"Consolas,",serif; color:black" lang="EN-US">
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<span style="font-family:"Consolas,",serif; color:black" lang="EN-US"> </span><span style="font-family:"Consolas,",serif; color:blue" lang="EN-US">return</span><span style="font-family:"Consolas,",serif; color:black" lang="EN-US"> a > b? a : b;</span></p>
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<span style="font-family:"Consolas,",serif; color:black">}</span></p>
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<span style="" lang="EN-US">and select is defined as </span></p>
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<span style="" lang="EN-US"> </span></p>
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<span style="font-size:12.0pt; font-family:"Arial",sans-serif; color:#6D6E71" lang="EN-US">gentype <b>select</b>(gentype <i>a</i>, gentype <i>b</i>, igentype <i>c</i>) gentype <b>select</b>(gentype <i>a</i>, gentype <i>b</i>, ugentype <i>c</i>)</span></p>
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<span style="font-size:12.0pt; font-family:"Arial",sans-serif; color:#6D6E71" lang="EN-US">For each component of a vector type,</span></p>
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<i><span style="font-size:12.0pt; font-family:"Arial",sans-serif; color:#6D6E71" lang="EN-US">result[i]</span></i><span style="font-size:12.0pt; font-family:"Arial",sans-serif; color:#6D6E71" lang="EN-US"> = if MSB of <i>c[i]</i> is set ? <i>b[i]</i> : <i>a[i]</i>.</span></p>
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<span style="font-size:12.0pt; font-family:"Arial",sans-serif; color:#6D6E71" lang="EN-US">For a scalar type, <i>result</i> = <i>c</i> ? <i>b</i> : <i>a</i>.</span></p>
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<span style="font-size:10.0pt; font-family:Consolas; color:#264357; background:white" lang="EN-US">igentype</span><span style="font-size:12.0pt; font-family:"Arial",sans-serif; color:#6D6E71" lang="EN-US"> and </span><span style="font-size:10.0pt; font-family:Consolas; color:#264357; background:white" lang="EN-US">ugentype</span><span style="font-size:12.0pt; font-family:"Arial",sans-serif; color:#6D6E71" lang="EN-US"> must
have the same number of elements and bits as </span><span style="font-size:10.0pt; font-family:Consolas; color:#264357; background:white" lang="EN-US">gentype</span><sup><span style="font-size:9.0pt; font-family:"Arial",sans-serif; color:#6D6E71" lang="EN-US">36</span></sup><span style="font-size:12.0pt; font-family:"Arial",sans-serif; color:#6D6E71" lang="EN-US">.</span></p>
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<span style="" lang="EN-US">I guess, if we convert predicate elements to bool, we should get the same behavior.</span></p>
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<b><span lang="EN-US">From:</span></b><span lang="EN-US"> Finkel, Hal J. <hfinkel@anl.gov>
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<b>Sent:</b> Tuesday, May 19, 2020 9:50 PM<br>
<b>To:</b> Bader, Alexey <alexey.bader@intel.com>; Anastasia Stulova <Anastasia.Stulova@arm.com>; Keane, Erich <erich.keane@intel.com>; Min-Yih Hsu <minyihh@uci.edu>; cfe-dev (cfe-dev@lists.llvm.org) <cfe-dev@lists.llvm.org><br>
<b>Cc:</b> nd <nd@arm.com><br>
<b>Subject:</b> Re: [cfe-dev] [RFC] Ternary operator with vector type predicate</span></p>
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<span style="font-size:12.0pt; color:black">Thanks, Alexey. In that case, do you have any thoughts on the original email in this thread?</span></p>
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<span style="font-size:12.0pt; color:black"> -Hal</span></p>
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<span style="font-size:10.0pt">Hal Finkel<br>
Lead, Compiler Technology and Programming Languages<br>
Leadership Computing Facility<br>
Argonne National Laboratory</span></p>
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<b><span style="color:black">From:</span></b><span style="color:black"> Bader, Alexey <<a href="mailto:alexey.bader@intel.com">alexey.bader@intel.com</a>><br>
<b>Sent:</b> Tuesday, May 19, 2020 1:48 PM<br>
<b>To:</b> Finkel, Hal J. <<a href="mailto:hfinkel@anl.gov">hfinkel@anl.gov</a>>; Anastasia Stulova <<a href="mailto:Anastasia.Stulova@arm.com">Anastasia.Stulova@arm.com</a>>; Keane, Erich <<a href="mailto:erich.keane@intel.com">erich.keane@intel.com</a>>;
Min-Yih Hsu <<a href="mailto:minyihh@uci.edu">minyihh@uci.edu</a>>; cfe-dev (<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>) <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Cc:</b> nd <<a href="mailto:nd@arm.com">nd@arm.com</a>><br>
<b>Subject:</b> RE: [cfe-dev] [RFC] Ternary operator with vector type predicate</span>
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<span lang="EN-US">Yes, we do implement these rules for OpenCL and they are applied to all OpenCL versions.</span></p>
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<span lang="EN-US"><a href="https://godbolt.org/z/YH6ExF">https://godbolt.org/z/YH6ExF</a></span></p>
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<b><span lang="EN-US">From:</span></b><span lang="EN-US"> cfe-dev <<a href="mailto:cfe-dev-bounces@lists.llvm.org">cfe-dev-bounces@lists.llvm.org</a>>
<b>On Behalf Of </b>Finkel, Hal J. via cfe-dev<br>
<b>Sent:</b> Tuesday, May 19, 2020 8:36 PM<br>
<b>To:</b> Anastasia Stulova <<a href="mailto:Anastasia.Stulova@arm.com">Anastasia.Stulova@arm.com</a>>; Keane, Erich <<a href="mailto:erich.keane@intel.com">erich.keane@intel.com</a>>; Min-Yih Hsu <<a href="mailto:minyihh@uci.edu">minyihh@uci.edu</a>>; clang
developer list <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Cc:</b> nd <<a href="mailto:nd@arm.com">nd@arm.com</a>><br>
<b>Subject:</b> Re: [cfe-dev] [RFC] Ternary operator with vector type predicate</span></p>
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<span style="font-size:12.0pt; color:black">Thanks, Anastasia. I have certainly used the ext_vector_type types outside of OpenCL mode in the past. Do we currently implement the OpenCL 2 ternary operator rules for these vectors?</span></p>
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<span style="font-size:12.0pt; color:black"> -Hal</span></p>
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<span style="font-size:10.0pt">Hal Finkel<br>
Lead, Compiler Technology and Programming Languages<br>
Leadership Computing Facility<br>
Argonne National Laboratory</span></p>
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<b><span style="color:black">From:</span></b><span style="color:black"> Anastasia Stulova <<a href="mailto:Anastasia.Stulova@arm.com">Anastasia.Stulova@arm.com</a>><br>
<b>Sent:</b> Tuesday, May 19, 2020 12:30 PM<br>
<b>To:</b> Keane, Erich <<a href="mailto:erich.keane@intel.com">erich.keane@intel.com</a>>; Min-Yih Hsu <<a href="mailto:minyihh@uci.edu">minyihh@uci.edu</a>>; Finkel, Hal J. <<a href="mailto:hfinkel@anl.gov">hfinkel@anl.gov</a>>; clang developer list <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Cc:</b> nd <<a href="mailto:nd@arm.com">nd@arm.com</a>><br>
<b>Subject:</b> Re: [cfe-dev] [RFC] Ternary operator with vector type predicate</span>
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<span style="font-size:12.0pt; color:black">I see ext_vector_type as a Clang extension that implements OpenCL rules under OpenCL mode. I believe there are areas where it behaves slightly differently if it's used in non-OpenCL code. I am not aware of details,
but I believe it is used outside of OpenCL mode too.</span></p>
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<span style="font-size:12.0pt; color:black">Anastasia</span></p>
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<b><span style="color:black">From:</span></b><span style="color:black"> cfe-dev <<a href="mailto:cfe-dev-bounces@lists.llvm.org">cfe-dev-bounces@lists.llvm.org</a>> on behalf of Finkel, Hal J. via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Sent:</b> 19 May 2020 14:22<br>
<b>To:</b> Keane, Erich <<a href="mailto:erich.keane@intel.com">erich.keane@intel.com</a>>; Min-Yih Hsu <<a href="mailto:minyihh@uci.edu">minyihh@uci.edu</a>><br>
<b>Cc:</b> <a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a> <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Subject:</b> Re: [cfe-dev] [RFC] Ternary operator with vector type predicate</span>
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<b><span style="color:black">From:</span></b><span style="color:black"> Keane, Erich <<a href="mailto:erich.keane@intel.com">erich.keane@intel.com</a>><br>
<b>Sent:</b> Tuesday, May 19, 2020 8:10 AM<br>
<b>To:</b> Finkel, Hal J. <<a href="mailto:hfinkel@anl.gov">hfinkel@anl.gov</a>>; Min-Yih Hsu <<a href="mailto:minyihh@uci.edu">minyihh@uci.edu</a>><br>
<b>Cc:</b> <a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a> <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Subject:</b> RE: [cfe-dev] [RFC] Ternary operator with vector type predicate</span><span style="color:#666666">
</span></p>
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<span style="color:#666666" lang="EN-US">What is the intent with the ext-vector-types? </span></p>
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<p class="x_xxxxmsonormal" style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: "Calibri", sans-serif;">
That's a really good question. I've always thought of them as a slightly-more-convenient version of the vector types, although I suppose that they're really supposed to be OpenCL vectors. The Clang extension docs say, "OpenCL vector types are created using
the ext_vector_type attribute. It supports the V.xyzw syntax and other tidbits as seen in OpenCL." Thus, for OpenCL, I suppose that it is supposed to do this: <a href="https://www.khronos.org/registry/OpenCL/specs/2.2/html/OpenCL_C.html#operators-ternary-selection">https://www.khronos.org/registry/OpenCL/specs/2.2/html/OpenCL_C.html#operators-ternary-selection</a></p>
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-Hal</p>
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<span style="color:#666666" lang="EN-US"> </span></p>
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<span style="color:#666666" lang="EN-US"> It seems to me that it is an incompatible extension without anyone really maintaining them, and slightly different SEMA rules (for seemingly no reason).</span></p>
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<span style="color:#666666" lang="EN-US"> </span></p>
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<span style="color:#666666" lang="EN-US">The conditional operator for the vector_size value was implemented as a GCC compatibility option, but no such motivation existed for ext-vetctor-types.</span></p>
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<span style="color:#666666" lang="EN-US">That said, the semantic analysis for this in ext-vector-types is sufficiently different that it wasn’t possible to combine implementations. The rules had diverged significantly at one point, so there wasn’t really a
way to do so compatibly.</span></p>
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<b><span style="color:#666666" lang="EN-US">From:</span></b><span style="color:#666666" lang="EN-US"> Finkel, Hal J. <<a href="mailto:hfinkel@anl.gov">hfinkel@anl.gov</a>>
<br>
<b>Sent:</b> Tuesday, May 19, 2020 6:05 AM<br>
<b>To:</b> Keane, Erich <<a href="mailto:erich.keane@intel.com">erich.keane@intel.com</a>>; Min-Yih Hsu <<a href="mailto:minyihh@uci.edu">minyihh@uci.edu</a>><br>
<b>Cc:</b> <a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a><br>
<b>Subject:</b> Re: [cfe-dev] [RFC] Ternary operator with vector type predicate</span></p>
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<p class="x_xxxxmsonormal" style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: "Calibri", sans-serif;">
<span style="color:#666666" lang="EN-US"> </span></p>
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<span style="font-size:12.0pt; color:black" lang="EN-US">In general, I don't like to see features supported by not-ext-vector types that are not supported by ext-vector types.</span></p>
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<span style="font-size:12.0pt; color:black" lang="EN-US">That having been said, is this related to our discussion on bool vectors:</span></p>
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<span style="font-size:12.0pt; color:black" lang="EN-US"> <a href="http://lists.llvm.org/pipermail/cfe-dev/2020-May/065434.html">http://lists.llvm.org/pipermail/cfe-dev/2020-May/065434.html</a></span></p>
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<span style="font-size:12.0pt; color:black" lang="EN-US"> -Hal</span></p>
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<span style="font-size:10.0pt; color:#666666" lang="EN-US">Hal Finkel<br>
Lead, Compiler Technology and Programming Languages<br>
Leadership Computing Facility<br>
Argonne National Laboratory</span></p>
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<b><span style="color:black" lang="EN-US">From:</span></b><span style="color:black" lang="EN-US"> cfe-dev <<a href="mailto:cfe-dev-bounces@lists.llvm.org">cfe-dev-bounces@lists.llvm.org</a>> on behalf of Min-Yih Hsu via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Sent:</b> Friday, May 8, 2020 1:17 PM<br>
<b>To:</b> Keane, Erich <<a href="mailto:erich.keane@intel.com">erich.keane@intel.com</a>><br>
<b>Cc:</b> <a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a> <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>><br>
<b>Subject:</b> Re: [cfe-dev] [RFC] Ternary operator with vector type predicate</span><span style="color:#666666" lang="EN-US">
</span></p>
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<span style="color:#666666" lang="EN-US">Interesting….then I think the question simply becomes whether we should support it in ext_vector_type as well.
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<span style="color:#666666" lang="EN-US">Thanks for the pointer</span></p>
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<span style="color:#666666" lang="EN-US">-Min</span></p>
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<span style="color:#666666" lang="EN-US">On May 8, 2020, at 11:04 AM, Keane, Erich <<a href="mailto:erich.keane@intel.com">erich.keane@intel.com</a>> wrote:</span></p>
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<span style="color:#666666" lang="EN-US"> </span></p>
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<span style="color:#666666" lang="EN-US">Note that this was implemented for non-ext-vector types here:</span></p>
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<span style="color:#666666" lang="EN-US"><a href="https://github.com/llvm/llvm-project/commit/349636d2bfc39a5c81a835a95d203a42d9f9301a"><span style="color:purple">https://github.com/llvm/llvm-project/commit/349636d2bfc39a5c81a835a95d203a42d9f9301a</span></a></span></p>
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<span style="color:#666666" lang="EN-US"> </span></p>
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<span style="color:#666666" lang="EN-US">Which matches the GCC version. <span class="x_xxxxxapple-converted-space"> </span></span></p>
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<span style="color:#666666" lang="EN-US">The attribute is vector_size, not ext_vector_type however.</span></p>
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<span style="color:#666666" lang="EN-US"> </span></p>
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<span style="color:#666666" lang="EN-US">Otherwise, it does everything you’re proposing (like I said, just with a more portable vector-type definition).</span></p>
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<b><span style="color:#666666" lang="EN-US">From:</span></b><span class="x_xxxxxapple-converted-space"><span style="color:#666666" lang="EN-US"> </span></span><span style="color:#666666" lang="EN-US">cfe-dev <<a href="mailto:cfe-dev-bounces@lists.llvm.org">cfe-dev-bounces@lists.llvm.org</a>><span class="x_xxxxxapple-converted-space"> </span><b>On
Behalf Of<span class="x_xxxxxapple-converted-space"> </span></b>Min-Yih Hsu via cfe-dev<br>
<b>Sent:</b><span class="x_xxxxxapple-converted-space"> </span>Friday, May 8, 2020 10:58 AM<br>
<b>To:</b><span class="x_xxxxxapple-converted-space"> </span><a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a><br>
<b>Subject:</b><span class="x_xxxxxapple-converted-space"> </span>[cfe-dev] [RFC] Ternary operator with vector type predicate</span></p>
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<span style="color:#666666" lang="EN-US">Hi folks,</span></p>
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<span style="color:#666666" lang="EN-US">In clang’s vector extension, the ternary operator (?:) is able to select from two vector type values based on the boolean type predicate. For example:</span></p>
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<span style="color:#666666" lang="EN-US">```</span></p>
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<span style="color:#666666" lang="EN-US">typedef float float4 __attribute__((ext_vector_type(4)));</span></p>
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<span style="color:#666666" lang="EN-US">float4 foo(bool cond, float4 a, float4 b) {</span></p>
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<span style="color:#666666" lang="EN-US"> return cond? a : b;</span></p>
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<span style="color:#666666" lang="EN-US">}</span></p>
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<span style="color:#666666" lang="EN-US">```</span></p>
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<p class="x_xxxxmsonormal" style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: "Calibri", sans-serif;">
<span style="color:#666666" lang="EN-US">However, clang currently doesn’t support vector type values as the predicates. So code shown below won’t compile:</span></p>
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<span style="color:#666666" lang="EN-US">```</span></p>
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<span style="color:#666666" lang="EN-US">float4 foo(float4 a, float4 b) {</span></p>
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<span style="color:#666666" lang="EN-US"> return a > b? a : b;</span></p>
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<span style="color:#666666" lang="EN-US">```</span></p>
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<p class="x_xxxxmsonormal" style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: "Calibri", sans-serif;">
<span style="color:#666666" lang="EN-US">Which is essentially just a max function that can be implemented by hardware instructions (vmaxps in Intel AVX for example) efficiently.</span></p>
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<span style="color:#666666" lang="EN-US">I’m proposing to support vector type values as predicates in the ternary operator: If the predicate value has vector type, each of its element would be converted to bool before being used to select corresponding elements
from the second or third operands. Note that this is exactly what GCC is doing right now [1] in their vector extensions.</span></p>
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<span style="color:#666666" lang="EN-US"> </span></p>
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<span style="color:#666666" lang="EN-US">On the (IR) codegen side, since the IR `select`, `icmp`, and `fcmp` instruction all support vector type values as the operands, I don’t think there are much trouble in it.</span></p>
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<span style="color:#666666" lang="EN-US">Here are the reasons and some advantages:</span></p>
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<span style="color:#666666" lang="EN-US">1. It provides more flexibility for programmers to do conditional selections on vectors. Especially for cases that can be optimized by hardware instructions like the motivated example above.</span></p>
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<span style="color:#666666" lang="EN-US"> </span></p>
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<span style="color:#666666" lang="EN-US">2. It will not break the current usages of ternary operator: If the predicate is a scalar value, it’s still sticking to the current model.</span></p>
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<span style="color:#666666" lang="EN-US"> </span></p>
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<span style="color:#666666" lang="EN-US">3. If the goal of our extensions is aiming to “support a broad range of GCC extensions”. Then the behavior should also be as consistent as possible.</span></p>
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<span style="color:#666666" lang="EN-US">I’ll try to come up with a patch for preview as soon as possible.</span></p>
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<span style="color:#666666" lang="EN-US">Also a slightly off-topic thing: In our document [2], the ternary operator has always been mis-typed as ‘:?’ Maybe we should fix it some times.</span></p>
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<span style="color:#666666" lang="EN-US"> </span></p>
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<p class="x_xxxxmsonormal" style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: "Calibri", sans-serif;">
<span style="color:#666666" lang="EN-US">Thanks for the feedbacks in advance.</span></p>
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<span style="color:#666666" lang="EN-US">-Min</span></p>
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<span style="color:#666666" lang="EN-US">[1]: <a href="https://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html"><span style="color:purple">https://gcc.gnu.org/onlinedocs/gcc/Vector-Extensions.html</span></a></span></p>
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<span style="color:#666666" lang="EN-US">[2]: <a href="https://clang.llvm.org/docs/LanguageExtensions.html#vectors-and-extended-vectors"><span style="color:purple">https://clang.llvm.org/docs/LanguageExtensions.html#vectors-and-extended-vectors</span></a></span></p>
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