erichkeane marked 2 inline comments as done.
erichkeane added inline comments.
================
Comment at: include/clang/Basic/AttrDocs.td:252
+declaration to specify that the return value of the function (which must be a
+pointer type) has an alignment specified by the indicated parameter. The
+alignment parameter is one-based. In the case of member functions, the
----------------
rjmccall wrote:
> "that the return value of the function ... is at least as aligned as the
> value of the indicated parameter. The parameter is given by its index
> in the list of formal parameters; the first parameter has index 1 unless
> the function is a C++ non-static member function, in which case the
> first parameter has index 2 to account for the implicit ``this`` parameter."
>
> What's the behavior of this attribute if the given attribute is not a power
> of 2?
> Does it silently have no effect, or is it U.B.?
Thanks for the wording, I like this.
It isn't checked for that, so I'll say UB. A little bit of a caveat emptor
here.
================
Comment at: include/clang/Basic/AttrDocs.td:270
+condition that the code already ensures is true. It does not cause the compiler
+to enforce the provided alignment assumption.
+ }];
----------------
rjmccall wrote:
> "Note that this attribute merely informs the compiler that a function always
> returns a sufficiently aligned pointer. It does not cause the compiler to
> emit
> code to enforce that alignment. The behavior is undefined if the returned
> pointer is not sufficiently aligned."
Thanks again!
================
Comment at: lib/CodeGen/CGCall.cpp:4352
+ } else if (const auto *AA = TargetDecl->getAttr<AllocAlignAttr>()) {
+ llvm::Value *ParamVal = IRCallArgs[AA->getParamIndex() - 1];
+ EmitAlignmentAssumption(Ret.getScalarVal(), ParamVal);
----------------
rjmccall wrote:
> IRCallArgs is not one-to-one with the list of formal parameters. You need to
> be taking the value out of CallArgList. Three test cases come to mind:
>
> 1. There's an earlier struct argument which expands to no IR arguments.
> 2. There's an earlier struct argument which expands to multiple IR arguments.
> 3. The alignment argument itself expands to multiple IR arguments. For
> example, __int128_t on x86-64.
Awesome, thanks for the info! I'll change that.
https://reviews.llvm.org/D29599
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