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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I think the problem is that the borderline for IR being target independent is very vague in general. In this case specifically the issue is that the Spec is
very explicit about threating this as 4 element aligned type. However, I agree this lowering could be done later as well. The approach to condition this on the Target property sounds reasonable. I think we have other places in Clang where vec3 is threated
as vec4 (e.g. ScalarExprEmitter::VisitAsTypeExpr). Those would have to be handled too. Feel free to propose a prototype.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Cheer,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Anastasia<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"> cfe-dev [mailto:cfe-dev-bounces@lists.llvm.org]
<b>On Behalf Of </b>jingu@codeplay.com via cfe-dev<br>
<b>Sent:</b> 08 March 2017 11:01<br>
<b>To:</b> aleksey.bader@gmail.com<br>
<b>Cc:</b> 'cfe-dev@lists.llvm.org' (cfe-dev@lists.llvm.org)<br>
<b>Subject:</b> Re: [cfe-dev] Question about "CodeGenFunction::EmitLoadOfScalar" with vector type of 3 elements<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Hi Alexey,<br>
<br>
I appreciate your response. My colleague and I are implementing a transformation pass between LLVM IR and another IR and we want to keep the 3-component vector types in our target IR. As you mentioned, the 4-component vector type conversion code is not problem.
But I usually expect clang generates more target independent LLVM IR except target specific properties like calling convention, memory layout of variables, etc. clang can keep the 3-component vector type operations and llvm codegen can handle them according
to target. At present, we're having to undo Clang's transformation of vec3 -> vec4, to recreate the original type information, which is unfortunate. Would it be possible to add an option to control the behaviour?<br>
<br>
Thanks,<br>
<br>
JinGu Kang<br>
<br>
<o:p></o:p></p>
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<p class="MsoNormal">On 07/03/17 18:19, <a href="mailto:aleksey.bader@gmail.com">
aleksey.bader@gmail.com</a> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hi JinGu, <o:p></o:p></p>
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<p class="MsoNormal">I don't think it should be a problem for OpenCL. 3-component vector is aligned as 4-component vector (see section 6.1.5 "Alignment of Type" of OpenCL C kernel language specification v2.0).<o:p></o:p></p>
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<p class="MsoNormal">AFAIK, almost all existing OpenCL compilers are based on clang and there seems to be no problems with handling load/store operations this way.<o:p></o:p></p>
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<p class="MsoNormal">Could you elaborate on the case where this approach doesn't work?<o:p></o:p></p>
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<p class="MsoNormal">Thanks,<o:p></o:p></p>
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<p class="MsoNormal">Alexey<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Mon, Mar 6, 2017 at 6:47 PM, <a href="mailto:jingu@codeplay.com">
jingu@codeplay.com</a> via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
<p class="MsoNormal">Hi All,<br>
<br>
<br>
I have a question about "CodeGenFunction::EmitLoadOfScalar". I am compiling code with vector type of 3 elements like int3 or float3. Clang converts the vector load to different vector load with 4 element vector type because there is code on "CodeGenFunction::EmitLoadOfScalar"
as follows:<br>
<br>
1312 // For better performance, handle vector loads differently.<br>
1313 if (Ty->isVectorType()) {<br>
1314 const llvm::Type *EltTy = Addr.getElementType();<br>
1315<br>
1316 const auto *VTy = cast<llvm::VectorType>(EltTy);<br>
1317<br>
1318 // Handle vectors of size 3 like size 4 for better performance.<br>
1319 if (VTy->getNumElements() == 3) {<br>
1320<br>
1321 // Bitcast to vec4 type.<br>
1322 llvm::VectorType *vec4Ty = llvm::VectorType::get(VTy->getElementType(),<br>
1323 4);<br>
1324 Address Cast = Builder.CreateElementBitCast(Addr, vec4Ty, "castToVec4");<br>
1325 // Now load value.<br>
1326 llvm::Value *V = Builder.CreateLoad(Cast, Volatile, "loadVec4");<br>
<br>
4 element vector load could generate aligned vector load in the end and it would be better in usual. But it is not good for other target or language like OpenCL which supports 3 element vector type natively. Can we consider this situation on "CodeGenFunction::EmitLoadOfScalar"
like this "if (!getLangOpts().OpenCL)" or with target specific property on TargetCodeGenInfo?<br>
<br>
If I missed something, please let me know.<br>
<br>
Thanks,<br>
JinGu Kang<br>
<br>
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