[PATCH] Support the assume_aligned function attribute

[Aaron Ballman]

On Mon, Jul 21, 2014 at 12:36 PM, Hal Finkel <hfinkel at anl.gov> wrote:
> ----- Original Message -----
>> From: "Aaron Ballman" <aaron.ballman at gmail.com>
>> To: "Hal Finkel" <hfinkel at anl.gov>
>> Cc: "Richard Smith" <richard at metafoo.co.uk>, "llvm cfe" <cfe-commits at cs.uiuc.edu>,
>> reviews+D4601+public+521bc0d2736e59d3 at reviews.llvm.org
>> Sent: Monday, July 21, 2014 11:33:17 AM
>> Subject: Re: [PATCH] Support the assume_aligned function attribute
>>
>> On Mon, Jul 21, 2014 at 12:25 PM, Hal Finkel <hfinkel at anl.gov> wrote:
>> > ----- Original Message -----
>> >> From: "Aaron Ballman" <aaron.ballman at gmail.com>
>> >> To: reviews+D4601+public+521bc0d2736e59d3 at reviews.llvm.org
>> >> Cc: "Hal Finkel" <hfinkel at anl.gov>, "Richard Smith"
>> >> <richard at metafoo.co.uk>, "llvm cfe" <cfe-commits at cs.uiuc.edu>
>> >> Sent: Monday, July 21, 2014 11:22:01 AM
>> >> Subject: Re: [PATCH] Support the assume_aligned function attribute
>> >>
>> >> On Sun, Jul 20, 2014 at 7:25 PM, Richard Smith
>> >> <richard at metafoo.co.uk> wrote:
>> >> > Somewhat unrelated to this patch in particular, but we should
>> >> > add a
>> >> > UBSan check to catch failed assumptions.
>> >> >
>> >> > ================
>> >> > Comment at: include/clang/Basic/Attr.td:867
>> >> > @@ +866,3 @@
>> >> > +                             "ExpectedFunctionOrMethod">;
>> >> > +  let Args = [IntArgument<"Alignment">,
>> >> > DefaultIntArgument<"Offset", 0>];
>> >> > +  let Documentation = [Undocumented];
>> >> > ----------------
>> >> > These should probably both be `ExprArgument`s, in order to
>> >> > support
>> >> > dependent alignment/offset expressions in templates.
>> >> >
>> >> > ================
>> >> > Comment at: include/clang/Basic/Attr.td:868
>> >> > @@ +867,3 @@
>> >> > +  let Args = [IntArgument<"Alignment">,
>> >> > DefaultIntArgument<"Offset", 0>];
>> >> > +  let Documentation = [Undocumented];
>> >> > +}
>> >> > ----------------
>> >> > Please add documentation.
>> >> >
>> >> > ================
>> >> > Comment at: lib/CodeGen/CGExpr.cpp:3352
>> >> > @@ +3351,3 @@
>> >> > +
>> >> > +  if (Ret.isScalar() && TargetDecl)
>> >> > +    if (const AssumeAlignedAttr *AA =
>> >> > ----------------
>> >> > Please add parens around this `if`.
>> >> >
>> >> > ================
>> >> > Comment at: lib/Sema/SemaDeclAttr.cpp:1219-1227
>> >> > @@ +1218,11 @@
>> >> > +
>> >> > +  if (Attr.getNumArgs() > 2) {
>> >> > +    S.Diag(Attr.getLoc(),
>> >> > diag::err_attribute_too_many_arguments)
>> >> > +      << Attr.getName() << 2;
>> >> > +    return;
>> >> > +  } else if (Attr.getNumArgs() < 1) {
>> >> > +    S.Diag(Attr.getLoc(),
>> >> > diag::err_attribute_too_few_arguments)
>> >> > +      << Attr.getName() << 1;
>> >> > +    return;
>> >> > +  }
>> >> > +
>> >> > ----------------
>> >> > I think there's a helper function for this sequence of
>> >> > checks/diagnostics. If not, there should be.
>> >>
>> >> They aren't required -- the common handler takes care of that
>> >> stuff.
>> >
>> > No, I put them in specifically because the common handler did not.
>> > I noticed because when I was writing the regression tests, if I
>> > passed too few parameters (specifically none), the later call to
>> > getArg would assert.
>>
>> Ahhhh shoot, the optional argument is why that's needed (see
>> handleCommonAttributeFeatures()). Sorry for leading you astray there;
>> I forgot that I hadn't gotten around to implementing optional
>> argument
>> handlers there yet (which is where this logic really should live).
>
> Where is that? If you don't get to it first, I'll just implement the correct logic there.

Just to circle back around on this, I got around to implementing this
today in r214407. So *now* you should be able to elide the manual arg
count checking with this patch.

~Aaron