[LLVMdev] [RFC] Passing Options to Different Parts of the Compiler Using Attributes

Bill Wendling wendling at apple.com
Tue Dec 4 22:05:32 PST 2012

On Dec 4, 2012, at 8:12 PM, Meador Inge <meadori at codesourcery.com> wrote:

> On Nov 26, 2012, at 3:20 PM, Bill Wendling wrote:
>>> 4. Do we really want the attribute references limited to a number?  Code will be more readable
>>>    if you can use actual names that indicate the intent.  For example:
>>>       attrgroup #compile_options = { … }
>>>       void @foo attrgroup(#compile_options)
>> The problem with this is it limits the number of attribute groups to a specific set -- compile options, non-compile options, etc.. There could be many different attribute groups involved, especially during LTO. I realize that the names will be uniqued. But that just adds a number to the existing name. I also want to avoid partitioning of the attributes into arbitrary groups -- i.e., groups with specific names which imply their usage or type.
> My main concern is that I see no reason to limit the id to just numbers in the *language definition*.
> That doesn't mean you can't always generate #<number> (in the same way that we do for variable names).
> This way it leaves open the possibility of hand-writing nice names.
Okay. It shouldn't be too difficult to do that.

>>> In other words, I think something like the following might be nicer:
>>> attribute_group := attributes <attrgroup_id> = { <attribute_list> }
>>> attrgroup_id    := #<id>
>>> attribute_list  := <attribute> ( <attribute>)*
>>> attribute       := <name> (= <value>)?
>>>               | <attribuge_id>
>>> function_def    := <attribute_list> <result_type> @<id> ([argument_list]) <attribute_list>
>> So something like this (no references inside of the 'attributes' statement allowed, cf. above)?
>> 	attributes #1 = { noinline, alignstack=4 }
>> 	attributes #2 = { "no-sse" }
>> 	define void @foo() #1 #2 { ret void }
>> This seems reasonable to me.
> Me too.  This seem pretty close to what was implemented in the patches posted on
> llvm-commits.  I review those in a bit.
I made one change. I made the attributes in the attribute groups non-comma separated. Otherwise, it's pretty much the same.


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