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<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">Hi Craig,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">I am Charles Li from Sony Playstation.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">We are doing x86 code gen testing and, by chance, we noticed that compiling the
<span style="color:#1F497D"><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__msdn.microsoft.com_en-2Dus_library_windows_hardware_ff561499-28v-3Dvs.85-29.aspx&d=AwMFAg&c=8hUWFZcy2Z-Za5rBPlktOQ&r=Mfk2qtn1LTDThVkh6-oGglNfMADXfJdty4_bhmuhMHA&m=nopqkvpGYmcsdlR7H2xIOQ9HPdZfvtEEy6kO5GPk520&s=PUlaa4M5pcc8VtoUZQRW7if5I2b_KPS_5rEd04MmiE4&e=">64-bit assembly instruction</a></span> “</span><span style="font-family:"Lucida Console";color:#002060">jrcxz</span><span style="font-family:"Arial","sans-serif"">”
in 32-bit mode<span style="color:#1F497D"> “-m32”</span> <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">previously resulted in an error,
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">now gets silently converted into the 32-bit equivalent instruction “</span><span style="font-family:"Lucida Console";color:#002060">jecxz</span><span style="font-family:"Arial","sans-serif"">”.<o:p></o:p></span></p>
<h1><span style="font-size:11.0pt;font-family:"Arial","sans-serif";font-weight:normal">I have bisected this change in behavior down to
<a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20141229/250681.html">
r225075 - [X86] Make the instructions that use AdSize16/32/64 co-exist together without using mode predicates.</a><span style="color:black"><o:p></o:p></span></span></h1>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">I am curious if this change in behavior was an intended feature or perhaps a side effect.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">Here is my methodology.<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:.5in"><span style="font-family:"Arial","sans-serif"">The asm test case.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#00B050">$ cat j64.s<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#002060"> jrcxz foo<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#002060">foo:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-indent:.5in"><span style="font-family:"Arial","sans-serif"">Compiling the test case in 32-bit mode with Clang r225039.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#00B050">$ r225039/clang.exe j64.s -c -m32 -target x86_64-pc-linux-gnu<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#002060">j64.s:1:9: error: instruction requires: 64-bit mode<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#002060"> jrcxz foo<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#002060"> ^<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-indent:.5in"><span style="font-family:"Arial","sans-serif"">Compiling the test case in 32-bit mode with Clang r225079 then disassembling the obj file to look for the jump instruction.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#00B050">$ r225079/clang.exe j64.s -c -m32 -target x86_64-pc-linux-gnu<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:Consolas">(No Error)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#00B050">$ objdump j64.o -d | grep j<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#002060">j64.o: file format elf32-i386<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in;text-autospace:none"><span style="font-family:"Lucida Console";color:#002060"> 0: e3 00 jecxz 2 <foo><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<h1><span style="font-size:11.0pt;font-family:"Arial","sans-serif";font-weight:normal">Just FYI, this is not blocking us in any way. I found this to be a very interesting discovery so I want to share it in the hopes of determining if it was intentional or not.<o:p></o:p></span></h1>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">Sincerely,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif"">Charles Li<o:p></o:p></span></p>
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