Add support for a union type in LLVM IR. Patch by Talin!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96011 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 109 insertions, 32 deletions

diff --git a/docs/LangRef.html b/docs/LangRef.html
index 9590609..b337b6a 100644
--- a/docs/LangRef.html
+++ b/docs/LangRef.html
@@ -66,12 +66,17 @@
       </li>
       <li><a href="#t_derived">Derived Types</a>
         <ol>
-          <li><a href="#t_array">Array Type</a></li>
+          <li><a href="#t_aggregate">Aggregate Types</a>
+            <ol>
+              <li><a href="#t_array">Array Type</a></li>
+              <li><a href="#t_struct">Structure Type</a></li>
+              <li><a href="#t_pstruct">Packed Structure Type</a></li>
+              <li><a href="#t_union">Union Type</a></li>
+              <li><a href="#t_vector">Vector Type</a></li>
+            </ol>
+          </li>
           <li><a href="#t_function">Function Type</a></li>
           <li><a href="#t_pointer">Pointer Type</a></li>
-          <li><a href="#t_struct">Structure Type</a></li>
-          <li><a href="#t_pstruct">Packed Structure Type</a></li>
-          <li><a href="#t_vector">Vector Type</a></li>
           <li><a href="#t_opaque">Opaque Type</a></li>
         </ol>
       </li>
@@ -1404,6 +1409,7 @@ Classifications</a> </div>
           <a href="#t_pointer">pointer</a>,
           <a href="#t_vector">vector</a>,
           <a href="#t_struct">structure</a>,
+          <a href="#t_union">union</a>,
           <a href="#t_array">array</a>,
           <a href="#t_label">label</a>,
           <a href="#t_metadata">metadata</a>.
@@ -1418,12 +1424,12 @@ Classifications</a> </div>
     </tr>
     <tr>
       <td><a href="#t_derived">derived</a></td>
-      <td><a href="#t_integer">integer</a>,
-          <a href="#t_array">array</a>,
+      <td><a href="#t_array">array</a>,
           <a href="#t_function">function</a>,
           <a href="#t_pointer">pointer</a>,
           <a href="#t_struct">structure</a>,
           <a href="#t_pstruct">packed structure</a>,
+          <a href="#t_union">union</a>,
           <a href="#t_vector">vector</a>,
           <a href="#t_opaque">opaque</a>.
       </td>
@@ -1561,6 +1567,21 @@ Classifications</a> </div>
    possible to have a two dimensional array, using an array as the element type
    of another array.</p>
 
+   
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection"> <a name="t_aggregate">Aggregate Types</a> </div>
+
+<div class="doc_text">
+
+<p>Aggregate Types are a subset of derived types that can contain multiple
+  member types. <a href="#t_array">Arrays</a>,
+  <a href="#t_struct">structs</a>, <a href="#t_vector">vectors</a> and
+  <a href="#t_union">unions</a> are aggregate types.</p>
+
+</div>
+
 </div>
 
 <!-- _______________________________________________________________________ -->
@@ -1629,9 +1650,9 @@ Classifications</a> </div>
 <h5>Overview:</h5>
 <p>The function type can be thought of as a function signature.  It consists of
    a return type and a list of formal parameter types. The return type of a
-   function type is a scalar type, a void type, or a struct type.  If the return
-   type is a struct type then all struct elements must be of first class types,
-   and the struct must have at least one element.</p>
+   function type is a scalar type, a void type, a struct type, or a union
+   type.  If the return type is a struct type then all struct elements must be
+   of first class types, and the struct must have at least one element.</p>
 
 <h5>Syntax:</h5>
 <pre>
@@ -1754,6 +1775,53 @@ Classifications</a> </div>
 </div>
 
 <!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection"> <a name="t_union">Union Type</a> </div>
+
+<div class="doc_text">
+
+<h5>Overview:</h5>
+<p>A union type describes an object with size and alignment suitable for
+   an object of any one of a given set of types (also known as an "untagged"
+   union). It is similar in concept and usage to a
+   <a href="#t_struct">struct</a>, except that all members of the union
+   have an offset of zero. The elements of a union may be any type that has a
+   size. Unions must have at least one member - empty unions are not allowed.
+   </p>
+
+<p>The size of the union as a whole will be the size of its largest member,
+   and the alignment requirements of the union as a whole will be the largest
+   alignment requirement of any member.</p>
+
+<p>Unions members are accessed using '<tt><a href="#i_load">load</a></tt> and
+   '<tt><a href="#i_store">store</a></tt>' by getting a pointer to a field with
+   the '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.
+   Since all members are at offset zero, the getelementptr instruction does
+   not affect the address, only the type of the resulting pointer.</p>
+
+<h5>Syntax:</h5>
+<pre>
+  union { &lt;type list&gt; }
+</pre>
+
+<h5>Examples:</h5>
+<table class="layout">
+  <tr class="layout">
+    <td class="left"><tt>union { i32, i32*, float }</tt></td>
+    <td class="left">A union of three types: an <tt>i32</tt>, a pointer to
+      an <tt>i32</tt>, and a <tt>float</tt>.</td>
+  </tr><tr class="layout">
+    <td class="left">
+      <tt>union {&nbsp;float,&nbsp;i32&nbsp;(i32)&nbsp;*&nbsp;}</tt></td>
+    <td class="left">A union, where the first element is a <tt>float</tt> and the
+      second element is a <a href="#t_pointer">pointer</a> to a
+      <a href="#t_function">function</a> that takes an <tt>i32</tt>, returning
+      an <tt>i32</tt>.</td>
+  </tr>
+</table>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
 <div class="doc_subsubsection"> <a name="t_pointer">Pointer Type</a> </div>
 
 <div class="doc_text">
@@ -1991,6 +2059,14 @@ Classifications</a> </div>
       the number and types of elements must match those specified by the
       type.</dd>
 
+  <dt><b>Union constants</b></dt>
+  <dd>Union constants are represented with notation similar to a structure with
+      a single element - that is, a single typed element surrounded
+      by braces (<tt>{}</tt>)).  For example: "<tt>{ i32 4 }</tt>".  The
+      <a href="#t_union">union type</a> can be initialized with a single-element
+      struct as long as the type of the struct element matches the type of
+      one of the union members.</dd>
+
   <dt><b>Array constants</b></dt>
   <dd>Array constants are represented with notation similar to array type
      definitions (a comma separated list of elements, surrounded by square
@@ -2009,7 +2085,8 @@ Classifications</a> </div>
 
   <dt><b>Zero initialization</b></dt>
   <dd>The string '<tt>zeroinitializer</tt>' can be used to zero initialize a
-      value to zero of <em>any</em> type, including scalar and aggregate types.
+      value to zero of <em>any</em> type, including scalar and
+      <a href="#t_aggregate">aggregate</a> types.
       This is often used to avoid having to print large zero initializers
       (e.g. for large arrays) and is always exactly equivalent to using explicit
       zero initializers.</dd>
@@ -3845,7 +3922,8 @@ Instruction</a> </div>
 
 <div class="doc_text">
 
-<p>LLVM supports several instructions for working with aggregate values.</p>
+<p>LLVM supports several instructions for working with
+  <a href="#t_aggregate">aggregate</a> values.</p>
 
 </div>
 
@@ -3862,14 +3940,14 @@ Instruction</a> </div>
 </pre>
 
 <h5>Overview:</h5>
-<p>The '<tt>extractvalue</tt>' instruction extracts the value of a struct field
-   or array element from an aggregate value.</p>
+<p>The '<tt>extractvalue</tt>' instruction extracts the value of a member field
+   from an <a href="#t_aggregate">aggregate</a> value.</p>
 
 <h5>Arguments:</h5>
 <p>The first operand of an '<tt>extractvalue</tt>' instruction is a value
-   of <a href="#t_struct">struct</a> or <a href="#t_array">array</a> type.  The
-   operands are constant indices to specify which value to extract in a similar
-   manner as indices in a
+   of <a href="#t_struct">struct</a>, <a href="#t_union">union</a>  or
+   <a href="#t_array">array</a> type.  The operands are constant indices to
+   specify which value to extract in a similar manner as indices in a
    '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.</p>
 
 <h5>Semantics:</h5>
@@ -3896,16 +3974,15 @@ Instruction</a> </div>
 </pre>
 
 <h5>Overview:</h5>
-<p>The '<tt>insertvalue</tt>' instruction inserts a value into a struct field or
-   array element in an aggregate.</p>
-
+<p>The '<tt>insertvalue</tt>' instruction inserts a value into a member field
+   in an <a href="#t_aggregate">aggregate</a> value.</p>
 
 <h5>Arguments:</h5>
 <p>The first operand of an '<tt>insertvalue</tt>' instruction is a value
-   of <a href="#t_struct">struct</a> or <a href="#t_array">array</a> type.  The
-   second operand is a first-class value to insert.  The following operands are
-   constant indices indicating the position at which to insert the value in a
-   similar manner as indices in a
+   of <a href="#t_struct">struct</a>, <a href="#t_union">union</a> or
+   <a href="#t_array">array</a> type.  The second operand is a first-class
+   value to insert.  The following operands are constant indices indicating
+   the position at which to insert the value in a similar manner as indices in a
    '<tt><a href="#i_getelementptr">getelementptr</a></tt>' instruction.  The
    value to insert must have the same type as the value identified by the
    indices.</p>
@@ -4107,8 +4184,8 @@ Instruction</a> </div>
 
 <h5>Overview:</h5>
 <p>The '<tt>getelementptr</tt>' instruction is used to get the address of a
-   subelement of an aggregate data structure. It performs address calculation
-   only and does not access memory.</p>
+   subelement of an <a href="#t_aggregate">aggregate</a> data structure.
+   It performs address calculation only and does not access memory.</p>
 
 <h5>Arguments:</h5>
 <p>The first argument is always a pointer, and forms the basis of the
@@ -4118,15 +4195,15 @@ Instruction</a> </div>
    indexes the pointer value given as the first argument, the second index
    indexes a value of the type pointed to (not necessarily the value directly
    pointed to, since the first index can be non-zero), etc. The first type
-   indexed into must be a pointer value, subsequent types can be arrays, vectors
-   and structs. Note that subsequent types being indexed into can never be
-   pointers, since that would require loading the pointer before continuing
-   calculation.</p>
+   indexed into must be a pointer value, subsequent types can be arrays,
+   vectors, structs and unions. Note that subsequent types being indexed into
+   can never be pointers, since that would require loading the pointer before
+   continuing calculation.</p>
 
 <p>The type of each index argument depends on the type it is indexing into.
-   When indexing into a (optionally packed) structure, only <tt>i32</tt> integer
-   <b>constants</b> are allowed.  When indexing into an array, pointer or
-   vector, integers of any width are allowed, and they are not required to be
+   When indexing into a (optionally packed) structure or union, only <tt>i32</tt>
+   integer <b>constants</b> are allowed.  When indexing into an array, pointer
+   or vector, integers of any width are allowed, and they are not required to be
    constant.</p>
 
 <p>For example, let's consider a C code fragment and how it gets compiled to