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Hi,
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<div class="">You should repost this to <a href="mailto:llvm-dev@lists.llvm.org" class="">
llvm-dev@lists.llvm.org</a>. This list is purely for auto generated bugzilla emails.</div>
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<div class="">Cheers,</div>
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<div class="">James<br class="">
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<div class="">On 29 Aug 2016, at 14:19, Christudasan D via llvm-bugs <<a href="mailto:llvm-bugs@lists.llvm.org" class="">llvm-bugs@lists.llvm.org</a>> wrote:</div>
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<p class="MsoNormal">Greetings to all.</p>
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<p class="MsoNormal">I am facing a problem with LLVM 3.5 and suspect it is a bug. Here is my observation.</p>
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<p class="MsoNormal">I am trying to support a target specific function attribute for a particular target machine.
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<p class="MsoNormal">Having followed the steps specified in the compiler documentation, I see the attribute is passed to the backend if we include the attribute in the function definition. But this attribute is not propagate to the backend if I include it only
in the function’s prototype/declaration (in the C program). </p>
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<p class="MsoNormal">This virtual function (given below) invocation in clang/lib/CodeGen/CodeGenModule.cpp in clang is responsible for attaching the target specific attributes to the backend CodeGen objects (functions, variables etc.)</p>
<p class="MsoNormal" style="text-indent:0.5in">getTargetCodeGenInfo().SetTargetAttributes(D, GO, *this)</p>
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<p class="MsoNormal">I found that this virtual function is getting invoked only for function definitions and not for function declarations.</p>
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<p class="MsoNormal">Actual requirement:</p>
<p class="MsoNormal">Along with regular C functions we have special functions supported in the target and its definition and invocation will always come in different compilation units. There must be a way to recognize these special functions at the call-sites
during codegen in the backend. By attaching some info in the function prototype, we can recognize these special functions at the call-site during backend codegen. That’s why I thought of a new target specific attribute to achieve this purpose.</p>
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<p class="MsoNormal"><b class=""><u class="">Is it really a bug?</u></b></p>
<p class="MsoNormal">When I compile a program having function declarations/prototypes with generic attributes like
<span style="color:rgb(127,0,85)" class="">__attribute__</span><span style="" class="">((</span><b class=""><span style="color:rgb(127,0,85)" class="">const</span></b><span style="" class="">)), clang will add it to that function’s attributelist in the IR and
it will be available in the backend.</span></p>
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<p class="MsoNormal">Similarly I expected the target specific attribute should also be added to the attributelist available in the backend and I should be able to identify it using
<b class="">F.hasFnAttribute("XYZ")</b>, where XYZ is the new attribute name. </p>
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<p class="MsoNormal">Since I work with LLVM 3.5 code-base, I am not sure whether this issue (if it is really a bug) has already been fixed with recent compiler releases.</p>
<p class="MsoNormal">Please write to me. </p>
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<p class="MsoNormal">Thanks,</p>
<p class="MsoNormal">Christu </p>
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