<html><head><meta http-equiv="Content-Type" content="text/html charset=iso-8859-1"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div><div apple-content-edited="true"></div><div apple-content-edited="true"><br></div><div><div>On Feb 9, 2013, at 12:39 PM, Justin Holewinski <<a href="mailto:justin.holewinski@gmail.com">justin.holewinski@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr">Very nice!<div><br></div><div>Could we get this write-up added to the sphinx docs?</div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Sat, Feb 9, 2013 at 11:41 AM, Bill Wendling <span dir="ltr"><<a href="mailto:wendling@apple.com" target="_blank">wendling@apple.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Using the New Attributes Classes<br>
<br>
Attributes in LLVM have changed in some fundamental ways. It was necessary to do<br>
this to support expanding the attributes to encompass more than a handful of<br>
attributes --- e.g. command line options. The old way of handling attributes<br>
consisted of representing them as a bit mask of values. This bit mask was stored<br>
in a "list" structure that was reference counted. The advantage of this was that<br>
attributes could be manipulated with 'or's and 'and's. The disadvantage of this<br>
was that there was limited room for expansion, and virtually no support for<br>
attribute-value pairs other than alignment.<br>
<br>
In the new scheme, an Attribute object represents a single attribute that's<br>
uniqued. You use the "Attribute::get" methods to create a new Attribute<br>
object. An attribute can be a single "enum" value (the enum being the<br>
Attribute::AttrKind enum), a string representing a target-dependent attribute,<br>
or an attribute-value pair. Some examples:<br>
<br>
Target-independent: noinline, zext<br>
Target-dependent: "no-sse", "thumb2"<br>
Attribute-value pair: "cpu" = "cortex-a8", align = 4<br>
<br>
(Note: for an attribute value pair, we expect a target-dependent attribute to<br>
have a string for the value.)<br>
<br>
An Attribute object is designed to be passed around by value.<br>
<br>
Because attributes are no longer represented as a bit mask, you will need to<br>
convert any code which does treat them as a bit mask to use the new query<br>
methods on the Attribute class. This should be straight forward. If there is<br>
missing functionality on the Attribute class, which you feel should be there,<br>
please let me know about it.<br>
<br>
The next class is the AttributeSet class. This replaces the old AttributeList<br>
class. The AttributeSet stores a collection of Attribute objects for each kind<br>
of object that may have an attribute associated with it: the function as a<br>
whole, the return type, or the function's parameters. A function's attributes<br>
are at index "AttributeSet::FunctionIndex"; the return type's attributes are at<br>
index "AttributeSet::ReturnIndex"; and the function's parameters' attributes are<br>
at indices 1, ..., n (where 'n' is the number of parameters). Most methods on<br>
the AttributeSet class take an index parameter.<br>
<br>
An AttributeSet is also a uniqued and immutable object. You create an<br>
AttributeSet through the "AttributeSet::get" methods. You can add and remove<br>
attributes, which result in the creation of a new AttributeSet.<br>
<br>
An AttributeSet object is designed to be passed around by value.<br>
<br>
Note: It is advised that you do *not* use the AttributeSet "Introspection"<br>
methods (e.g. 'Raw', 'getRawPointer', etc.). These methods break encapsulation,<br>
and may be removed in a future release (i.e. 4.0).<br>
<br>
Lastly, we have a 'builder' class to help create the AttributeSet object without<br>
having to create several different intermediate uniqued AttributeSet<br>
objects. The AttrBuilder class allows you to add and remove attributes at<br>
will. The attributes won't be uniqued until you call the appropriate<br>
"AttributeSet::get" method.<br>
<br>
An AttrBuilder object is *not* designed to be passed around by value. It should<br>
be passed by reference.<br>
<br>
Note: It is advised that you do *not* use the "AttrBuilder::addRawValue()"<br>
method or the "AttrBuilder(uint64_t Val)" c'tor. These are for backwards<br>
compatibility and may be removed in a future release (i.e. 4.0).<br>
<br>
And that's basically it! A lot of functionality is hidden behind these classes,<br>
but the interfaces are pretty straight forward. Please let me know if you have<br>
any questions about how to use these classes, or if there is any functionality<br>
you feel is missing.<br>
<br>
-bw<br>
<br>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br><br><div>Thanks,</div><div><br></div><div>Justin Holewinski</div>
</div>
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