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<p class="MsoNormal"><span style="color:#1F497D">Anastasia,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks for the feedback.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Right all the sampler variables will become local (function scope).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I have some updates to the proposal by Brian’s suggestions to accommodate OpenCL C++’s needs since they represent the sampler initializer by struct.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Basically,<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">Change the builtin function name from
</span>__initialize_sampler to <span style="color:#1F497D"> </span><span style="color:#1F497D">__translate_sampler_initializer.</span><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">Keep the concrete struct type for sampler initializer in Khronos Clang.</span><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="color:#1F497D"><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="color:#1F497D">Change the argument of __translate_sampler_initializer from int to the sampler initializer struct. Clang will translate the OpenCL sampler literal to the sampler initializer struct first, then pass
it to __translate_sampler_initializer.</span><span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Here is the updated example:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal">sampler_t s = ADDR | NORM | FILT;<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">void f() {<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> g(s);<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">}<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in"><span style="font-family:Wingdings">ð</span><span style="font-size:7.0pt;font-family:"Times New Roman",serif">
</span>Llvm bitcode equivalent to (assuming __sampler is the opaque struct type to represent sampler_t):<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">// opaque struct type for sampler<o:p></o:p></p>
<p class="MsoNormal">struct __sampler;<o:p></o:p></p>
<p class="MsoNormal">// concrete sampler initializer struct type<o:p></o:p></p>
<p class="MsoNormal">struct __sampler_initializer {<o:p></o:p></p>
<p class="MsoNormal"> int addr;<o:p></o:p></p>
<p class="MsoNormal"> int normalization;<o:p></o:p></p>
<p class="MsoNormal"> int filter;<o:p></o:p></p>
<p class="MsoNormal">};<o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal">constant __sampler *__attribute__((always_inline)) __translate_sampler_initializer(struct __sampler_initializer); // a builtin function for translating sampler initializer<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">constant struct __sampler_initializer _SI = {ADDR, NORM, FILT};<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">void f() {<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> constant __sampler *_s = __translate_sampler_initializer(_SI);<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> g(_s);<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">}<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Sam<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> Anastasia Stulova [mailto:Anastasia.Stulova@arm.com]
<br>
<b>Sent:</b> Friday, June 10, 2016 10:16 AM<br>
<b>To:</b> Liu, Yaxun (Sam) <Yaxun.Liu@amd.com>; cfe-dev (cfe-dev@lists.llvm.org) <cfe-dev@lists.llvm.org>; Bader, Alexey (alexey.bader@intel.com) <alexey.bader@intel.com>; Pan, Xiuli <xiuli.pan@intel.com><br>
<b>Cc:</b> Tom Stellard <tom@stellard.net>; Sumner, Brian <Brian.Sumner@amd.com>; Tye, Tony <Tony.Tye@amd.com>; nd <nd@arm.com><br>
<b>Subject:</b> RE: [RFC][OpenCL] New representation for sampler_t and its literal initializer<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D">Hi Sam,</span><span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D">I agree the original implementation of sampler type in LLVM isn’t ideal.</span><span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D">Your approach seems sensible to me. Would this mean that all sampler variables will be transformed to local by Clang?</span><span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D">Thanks,</span><span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D">Anastasia </span><span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="color:#1F497D"> </span><span lang="EN-GB"><o:p></o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<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"> Liu, Yaxun (Sam) [</span><a href="mailto:Yaxun.Liu@amd.com"><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif">mailto:Yaxun.Liu@amd.com</span></a><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif">]
<br>
<b>Sent:</b> 09 June 2016 21:18<br>
<b>To:</b> cfe-dev (</span><a href="mailto:cfe-dev@lists.llvm.org"><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif">cfe-dev@lists.llvm.org</span></a><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif">); Anastasia Stulova; Bader, Alexey
(</span><a href="mailto:alexey.bader@intel.com"><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif">alexey.bader@intel.com</span></a><span style="font-size:10.0pt;font-family:"Tahoma",sans-serif">); Pan, Xiuli<br>
<b>Cc:</b> Tom Stellard; Sumner, Brian; Tye, Tony<br>
<b>Subject:</b> [RFC][OpenCL] New representation for sampler_t and its literal initializer</span><span lang="EN-GB"><o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><span lang="EN-GB"> <o:p></o:p></span></p>
<p class="MsoNormal">Hi,<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">Currently Clang use int32 to represent sampler_t, which have been a source of issue for some backends, because in some backends sampler_t cannot be represented by int32. They have to depend on kernel argument metadata and use IPA to find
the sampler arguments and global variables and transform them to target specific sampler type.<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">Khronos Clang spirv-1.0 branch (<a href="https://github.com/KhronosGroup/SPIR/tree/spirv-1.0">https://github.com/KhronosGroup/SPIR/tree/spirv-1.0</a> ) represents sampler_t as an opaque struct pointer. Also it represents sampler literal
as a concrete struct type, and cast its pointer to a pointer to the opaque struct type for sampler_t. However there are two issues with the way how sampler literal is represented:<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in">1.<span style="font-size:7.0pt;font-family:"Times New Roman",serif">
</span>Backends still need to translate the sampler initializer struct to target specific sampler initializer, and this transformation cannot be implemented by library functions. Instead, it needs to be done by passes.<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in">2.<span style="font-size:7.0pt;font-family:"Times New Roman",serif">
</span>Optimizer may try to optimize the sampler global variable initialized with a sampler initializer struct. The optimizer will assume the sampler contains the bits of the initializer struct and may do memory optimizations on it, which will cause difficulty
for backends to transform the samplers.<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">We think representing sampler as an opaque type is a good idea, which we suggest Clang trunk to adopt. And we propose a another way to represent sampler literal. Basically in Clang codegen we generate a function call for each reference
of a sampler global variable initialized with a sampler literal, e.g.<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">sampler_t s = 0;<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">void f() {<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> g(s);<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">}<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in"><span style="font-family:Wingdings">ð</span><span style="font-size:7.0pt;font-family:"Times New Roman",serif">
</span>Llvm bitcode equivalent to (assuming __sampler is the opaque struct type to represent sampler_t):<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">constant __sampler *__attribute__((always_inline)) __initialize_sampler(int); // a builtin function for initialize a sampler<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">void f() {<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> constant __sampler *_s = __initialize_sampler(0);<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> g(_s);<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">}<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">Each builtin library can implement its own __initialize_sampler(). Since the real sampler type tends to be architecture dependent, allowing it to be initialized by a library function simplifies backend design. A typical implementation of
__initialize_sampler could be a table lookup of real sampler literal values. Since its argument is always a literal, the returned pointer is known at compile time and easily optimized to finally become some literal values directly put into image read instructions.<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">The advantage of this representation is:<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in">1.<span style="font-size:7.0pt;font-family:"Times New Roman",serif">
</span>Robust - can be optimized without losing information<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in">2.<span style="font-size:7.0pt;font-family:"Times New Roman",serif">
</span>Easy to implement – can be implemented by library instead of pass<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">Your feedbacks are welcome. Thanks.<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal">Sam<span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoNormal"> <span lang="EN-GB"><o:p></o:p></span></p>
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