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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-IE link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>I use ‘</span><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>__attribute__((pure))</span><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>’ for fast math functions and some other intrinsic function I have added such as getting the current core ID. This tells the compiler that calling the same function with the same arguments will always return the same value. A function declared with this attribute is not supposed to have any side-effects such as altering global variables.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>So:<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal style='text-indent:36.0pt'><span style='font-family:"Courier New";color:black;mso-fareast-language:EN-US'>extern void *lookup(int) __attribute__((pure));<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'>might do what you need though.<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'> MartinO <o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Book Antiqua",serif;color:#943634;mso-fareast-language:EN-US'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'>From:</span></b><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'> llvm-dev [mailto:llvm-dev-bounces@lists.llvm.org] <b>On Behalf Of </b>Nat! via llvm-dev<br><b>Sent:</b> 09 January 2016 14:41<br><b>To:</b> llvm-dev <llvm-dev@lists.llvm.org><br><b>Subject:</b> [llvm-dev] Attribute for a invariant function ?<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-family:"Courier New"'>I have a read-only lookup table, which takes integer arguments. Optimally I would like to indicate in the C source, that the function is invariant (?), so that the superflous calls can be optimized away.<br><br>```<br>extern void *lookup( int a);<br><br>void foo( void)<br>{<br> void *a, *b;<br> <br> a = lookup( 0x12345678);<br> bar( a);<br><br> b = lookup( 0x12345678); // b guaranteed to be the same as a, no call to (slow) lookup needed<br> baz( b);<br>}<br>```<br><br>But I don't really find anything in clang or llvm in terms of function attributes. The best I could come up with is in the llvm code to use attributes "argmemonly=true" readonly=true". But still two calls did happen. (I am on 3.7)<br><br>Ciao<br> Nat!</span><span style='font-family:"tt",serif'><o:p></o:p></span></p></div></div></body></html>