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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">For x86_64 ABI, a minimum feature set of SSE2 is required.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D">Kevin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<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""> llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu]
<b>On Behalf Of </b>suyog sarda<br>
<b>Sent:</b> Thursday, April 09, 2015 11:27 AM<br>
<b>To:</b> LLVM Developers Mailing List; David Majnemer; Sanjay Patel<br>
<b>Subject:</b> [LLVMdev] MMX/SSE subtarget feature in IR<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi all,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I have a sample test case :<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">$ cat 1.c<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">int foo(int x, int y){<o:p></o:p></p>
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<p class="MsoNormal"> int z = x + y;<o:p></o:p></p>
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<p class="MsoNormal"> return z/2;<o:p></o:p></p>
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<p class="MsoNormal">}<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I tried to get its IR form with clang providing subtarget feature as mmx for target x86_64<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">$ clang -O3 -mmmx 1.c -S -emit-llvm<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">in the IR generated i can see the subtarget-features as function attribute :<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">"target-features"="+mmx"<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In the SelectionDAG phase in file "X86ISelLowering.cpp", i checked in one of the function what is the subtarget feature by calling few routines of Subtarget.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Subtarget->hasMMX() ------ true<o:p></o:p></p>
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<p class="MsoNormal">Subtarget->hasSSE1() ------ true<o:p></o:p></p>
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<p class="MsoNormal">Subtarget->hasSSE2() ------ true<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">These functions just compare the X86SSELevel with subtarget enum values like MMX, SSE1, SSE2 etc.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">hasMMX() { return X86SSELevel >= MMX}; // similar for others<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Now, enum values start from MMX and goes on increasing with SSE1, SSE2, etc.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">For the above test case, the X86SSELevel is set to SSE2, which is confusing, since i have explicitly specified the target feature as 'mmx'. Why the X86SSELevel is getting set to SSE2 despite providing target-feature as mmx? Is it something
to do with default feature of x86_64?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I wanted to distinguish my code generation based on subtarget feature for MMX and SSE, which i am unable to do so currently because of above scenario.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I am sure i am missing something fundamental, but unable to exactly find out what.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Can someone please help me out on above question?<o:p></o:p></p>
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<p class="MsoNormal"><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"><o:p> </o:p></p>
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<p class="MsoNormal">Regards,<o:p></o:p></p>
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<p class="MsoNormal">Suyog Sarda <o:p></o:p></p>
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