<li><a href="#metadata">Metadata Nodes and Metadata Strings</a>
<ol>
<li><a href="#tbaa">'<tt>tbaa</tt>' Metadata</a></li>
+ <li><a href="#tbaa.struct">'<tt>tbaa.struct</tt>' Metadata</a></li>
<li><a href="#fpmath">'<tt>fpmath</tt>' Metadata</a></li>
<li><a href="#range">'<tt>range</tt>' Metadata</a></li>
</ol>
<dd>This indicates that the pointer parameter specifies the address of a
structure that is the return value of the function in the source program.
This pointer must be guaranteed by the caller to be valid: loads and
- stores to the structure may be assumed by the callee to not to trap. This
- may only be applied to the first parameter. This is not a valid attribute
- for return values. </dd>
+ stores to the structure may be assumed by the callee to not to trap and
+ to be properly aligned. This may only be applied to the first parameter.
+ This is not a valid attribute for return values. </dd>
<dt><tt><b><a name="noalias">noalias</a></b></tt></dt>
<dd>This indicates that pointer values
8-bits. If omitted, the natural stack alignment defaults to "unspecified",
which does not prevent any alignment promotions.</dd>
- <dt><tt>p:<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
+ <dt><tt>p[n]:<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
<dd>This specifies the <i>size</i> of a pointer and its <i>abi</i> and
- <i>preferred</i> alignments. All sizes are in bits. Specifying
- the <i>pref</i> alignment is optional. If omitted, the
- preceding <tt>:</tt> should be omitted too.</dd>
+ <i>preferred</i> alignments for address space <i>n</i>. All sizes are in
+ bits. Specifying the <i>pref</i> alignment is optional. If omitted, the
+ preceding <tt>:</tt> should be omitted too. The address space,
+ <i>n</i> is optional, and if not specified, denotes the default address
+ space 0. The value of <i>n</i> must be in the range [1,2^23).</dd>
<dt><tt>i<i>size</i>:<i>abi</i>:<i>pref</i></tt></dt>
<dd>This specifies the alignment for an integer type of a given bit
<ul>
<li><tt>E</tt> - big endian</li>
<li><tt>p:64:64:64</tt> - 64-bit pointers with 64-bit alignment</li>
+ <li><tt>p1:32:32:32</tt> - 32-bit pointers with 32-bit alignment for
+ address space 1</li>
+ <li><tt>p2:16:32:32</tt> - 16-bit pointers with 32-bit alignment for
+ address space 2</li>
<li><tt>i1:8:8</tt> - i1 is 8-bit (byte) aligned</li>
<li><tt>i8:8:8</tt> - i8 is 8-bit (byte) aligned</li>
<li><tt>i16:16:16</tt> - i16 is 16-bit aligned</li>
<p>Structures may optionally be "packed" structures, which indicate that the
alignment of the struct is one byte, and that there is no padding between
the elements. In non-packed structs, padding between field types is inserted
- as defined by the TargetData string in the module, which is required to match
+ as defined by the DataLayout string in the module, which is required to match
what the underlying code generator expects.</p>
<p>Structures can either be "literal" or "identified". A literal structure is
</div>
+<!-- _______________________________________________________________________ -->
+<h4>
+ <a name="tbaa.struct">'<tt>tbaa.struct</tt>' Metadata</a>
+</h4>
+
+<div>
+
+<p>The <a href="#int_memcpy"><tt>llvm.memcpy</tt></a> is often used to implement
+aggregate assignment operations in C and similar languages, however it is
+defined to copy a contiguous region of memory, which is more than strictly
+necessary for aggregate types which contain holes due to padding. Also, it
+doesn't contain any TBAA information about the fields of the aggregate.</p>
+
+<p><tt>!tbaa.struct</tt> metadata can describe which memory subregions in a memcpy
+are padding and what the TBAA tags of the struct are.</p>
+
+<p>The current metadata format is very simple. <tt>!tbaa.struct</tt> metadata nodes
+ are a list of operands which are in conceptual groups of three. For each
+ group of three, the first operand gives the byte offset of a field in bytes,
+ the second gives its size in bytes, and the third gives its
+ tbaa tag. e.g.:</p>
+
+<div class="doc_code">
+<pre>
+!4 = metadata !{ i64 0, i64 4, metadata !1, i64 8, i64 4, metadata !2 }
+</pre>
+</div>
+
+<p>This describes a struct with two fields. The first is at offset 0 bytes
+ with size 4 bytes, and has tbaa tag !1. The second is at offset 8 bytes
+ and has size 4 bytes and has tbaa tag !2.</p>
+
+<p>Note that the fields need not be contiguous. In this example, there is a
+ 4 byte gap between the two fields. This gap represents padding which
+ does not carry useful data and need not be preserved.</p>
+
+</div>
+
<!-- _______________________________________________________________________ -->
<h4>
<a name="fpmath">'<tt>fpmath</tt>' Metadata</a>
projects / oota-llvm.git / blobdiff