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<p class="MsoNormal">Hi all,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve encountered an issue with x86 Intel asm syntax when using certain variable names.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">If you look at the following example, where I try to do a mov to a memory location named “flags2”, llvm- mc works fine:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">>cat test_good.s<o:p></o:p></p>
<p class="MsoNormal">mov eax, flags2<o:p></o:p></p>
<p class="MsoNormal">>llvm-mc.exe -x86-asm-syntax=intel test_good.s -o -<o:p></o:p></p>
<p class="MsoNormal"> .text<o:p></o:p></p>
<p class="MsoNormal"> movl flags2, %eax<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">But if the memory location is named “flags”, llvm-mc fails:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">>cat test_bad.s<o:p></o:p></p>
<p class="MsoNormal">mov eax, flags<o:p></o:p></p>
<p class="MsoNormal">>llvm-mc.exe -x86-asm-syntax=intel test_bad.s -o -<o:p></o:p></p>
<p class="MsoNormal">test_bad.s:1:1: error: invalid operand for instruction<o:p></o:p></p>
<p class="MsoNormal">mov eax, flags<o:p></o:p></p>
<p class="MsoNormal">^<o:p></o:p></p>
<p class="MsoNormal"> .text<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">After investigation, I saw that the memory location named “flags” was matched to the EFLAGS register in the
<span style="background:white;mso-highlight:white">MatchRegisterName</span>() function in the generated X86GenAsmMatcher.inc.<o:p></o:p></p>
<p class="MsoNormal"><span style="background:white;mso-highlight:white"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="background:white;mso-highlight:white">case 'f': // 1 string to match.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="background:white;mso-highlight:white"> if (memcmp(Name.data()+1, "lags", 4))<o:p></o:p></span></p>
<p class="MsoNormal"><span style="background:white;mso-highlight:white"> break;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="background:white;mso-highlight:white"> return 25; // "flags"</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So basically, what I’m seeing with “flags” (which should be a legit variable name) is that the X86AsmParser creates a reference to an implicit register instead of a reference to memory.<o:p></o:p></p>
<p class="MsoNormal">There are additional issues here as well - what if we compile to SSE, but use a variable named “ZMM0” which is a register in AVX-512? Should this be allowed?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">We probably need some way to mark the registers (using attributes or predicates?) so that we’d know which ones are part of the legal set of registers that can be referenced in the architecture we’re compiling too.<o:p></o:p></p>
<p class="MsoNormal">Do you think this is a good approach?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Marina<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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