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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'>Hi John, <o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'>The example you are listing seems to be similar to this bug: <a href="https://bugs.llvm.org/show_bug.cgi?id=20734">https://bugs.llvm.org/show_bug.cgi?id=20734</a> actually, whch a clang bug.<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'>This definitely looks like a bug to me – C++11 section 7.1.2 paragraph 4 clearly states</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'>“A string literal in the body of an extern inline function is the same object in different translation units.”</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'> </span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'>Data for extern inline functions should be placed in a comdat group, and it looks like we get this</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'>correct if an actual variable is used, e.g.</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'> </span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> extern inline const char *fn()</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> {</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> static const char str[] = "example";</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> return str;</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> }</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'> </span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'>generates</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'> </span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> $_Z2fnv = comdat any</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> $_ZZ2fnvE3str = comdat any</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> @_ZZ2fnvE3str = linkonce_odr constant [8 x i8] c"example\00", comdat, align 1</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> define linkonce_odr arm_aapcscc i8* @_Z2fnv() #1 comdat {</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> entry:</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> ret i8* getelementptr inbounds ([8 x i8], [8 x i8]* @_ZZ2fnvE3str, i32 0, i32 0)</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Courier New";color:#222222'> }</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'> </span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'>so I think string literals should be handled similarly.<o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p> </o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'> </span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><o:p></o:p></span></p><p class=MsoNormal style='background:white'><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#1F497D'>John</span><span style='font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222'><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><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> llvm-dev [mailto:llvm-dev-bounces@lists.llvm.org] <b>On Behalf Of </b>Sameer AbuAsal via llvm-dev<br><b>Sent:</b> Tuesday, March 21, 2017 6:42 PM<br><b>To:</b> llvm-dev@lists.llvm.org<br><b>Subject:</b> [llvm-dev] [ARM] [C++ standard] Correct linkage type for string literals in extern inline functions<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Hi, <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I came across this behavior irregularity in LLVM for ARM backend (-target arm-linux-gnueabi) with the constant promotion optimization in arm (-arm-promote-constant=true). <o:p></o:p></p><p class=MsoNormal>For the attached source files compiling with the following:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>clang++ -target arm-linux-gnueabi A.cpp B.cpp –o a.out<o:p></o:p></p><p class=MsoNormal>The addresses returned from bar() and foo() are not the same (string literals live in different memory locations) however, when we turn off the constant pool optimization<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>clang-arm-x++ -Ofast -mllvm -arm-promote-constant=false A.cpp B.cpp -o test_case.exe –o a.out <o:p></o:p></p><p class=MsoNormal>we are getting the same addresses for string literals.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Looking into the ll files , the strings are created as “private unnamed_addr constant” so the constant pool optimization pass is promoting them to constant pools and causing them to have different addresses, which seems fine.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Is this behavior in line with the C++ standard for strings in extern inline functions? If not, what should be the correct linkage type emitted for this constant? Is this a potential clang bug?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thank you,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>