[Lldb-commits] [PATCH] D30918: [debugserver] This is a small cleanup patch to AVX support detection

[Jason Molenda via Phabricator via lldb-commits]

jasonmolenda accepted this revision.
jasonmolenda added a comment.
This revision is now accepted and ready to land.

looks good to me.



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Comment at: tools/debugserver/source/MacOSX/x86_64/DNBArchImplX86_64.cpp:66
+  int error = ::sysctlbyname(feature, &answer, &answer_size, NULL, 0);
+  return !error & answer;
+}
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zturner wrote:
> jasonmolenda wrote:
> > I see what you're doing -- this can either return "false, meaning the sysctlbyname failed or I got a zero value, or true meaning it succeeded and I got a nonzero value" but the use of a bitwise AND is going to look like a bug to any casual reader and make them re-read the code a few times before they've realized it is intended (at least it did me).  It might be easier for future maintainers if it's written more like like
> > 
> > if (error != 0 && answer != 0)
> >   return true;
> > else
> >   return false;
> > 
> > and let the compiler come up with the shorter form when generating the instructions.
> Maybe I'm missing something, but why not just `return !error && answer`?
That would be fine too.  The bitwise in the original is correct, but needlessly confusing IMO.


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Comment at: tools/debugserver/source/MacOSX/x86_64/DNBArchImplX86_64.cpp:99
+  for (; first_letter < length; ++first_letter) {
+    if (buffer[first_letter] & 0x40)
+      break;
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jasonmolenda wrote:
> Would '@' be clearer here than 0x40?  I had to run man ascii to figure out what this was.  Maybe a comment saying that we expect the string from KERN_OSVERSION to be something like '11B156' & we're interested in the '11' bit would make it a little easier to read. (I had to run sysctl to look at the string you're parsing to follow along with the logic)
I misread this myself when writing the above.  isupper() is what you're doing - I'd recommend using that instead of the bit mask.


https://reviews.llvm.org/D30918