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Fully document the LLVM constants. This should go into LLVM 1.4

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@18701 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2004-12-09 17:30:23 +00:00
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@ -44,6 +44,13 @@
</ol>
</li>
<li><a href="#constants">Constants</a>
<ol>
<li><a href="#simpleconstants">Simple Constants</a>
<li><a href="#aggregateconstants">Aggregate Constants</a>
<li><a href="#globalconstants">Global Variable and Function Addresses</a>
<li><a href="#undefvalues">Undefined Values</a>
<li><a href="#constantexprs">Constant Expressions</a>
</ol>
</li>
<li><a href="#instref">Instruction Reference</a>
<ol>
@ -221,9 +228,6 @@ the parser.</p>
purposes:</p>
<ol>
<li>Numeric constants are represented as you would expect: 12, -3 123.421,
etc. Floating point constants have an optional hexadecimal notation.</li>
<li>Named values are represented as a string of characters with a '%' prefix.
For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual
regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'.
@ -234,6 +238,8 @@ purposes:</p>
<li>Unnamed values are represented as an unsigned numeric value with a '%'
prefix. For example, %12, %2, %44.</li>
<li>Constants, which are described in <a href="#constants">section about
constants</a></li>
</ol>
<p>LLVM requires that values start with a '%' sign for two reasons: Compilers
@ -293,16 +299,6 @@ demonstrating instructions, we will follow an instruction with a comment that
defines the type and name of value produced. Comments are shown in italic
text.</p>
<p>The one non-intuitive notation for constants is the optional hexidecimal form
of floating point constants. For example, the form '<tt>double
0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
4.5e+15</tt>' which is also supported by the parser. The only time hexadecimal
floating point constants are useful (and the only time that they are generated
by the disassembler) is when an FP constant has to be emitted that is not
representable as a decimal floating point number exactly. For example, NaN's,
infinities, and other special cases are represented in their IEEE hexadecimal
format so that assembly and disassembly do not cause any bits to change in the
constants.</p>
</div>
<!-- *********************************************************************** -->
@ -577,25 +573,39 @@ produced by instructions, passed as arguments, or used as operands to
instructions. This means that all structures and arrays must be
manipulated either by pointer or by component.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="t_derived">Derived Types</a> </div>
<div class="doc_text">
<p>The real power in LLVM comes from the derived types in the system.
This is what allows a programmer to represent arrays, functions,
pointers, and other useful types. Note that these derived types may be
recursive: For example, it is possible to have a two dimensional array.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="t_array">Array Type</a> </div>
<div class="doc_text">
<h5>Overview:</h5>
<p>The array type is a very simple derived type that arranges elements
sequentially in memory. The array type requires a size (number of
elements) and an underlying data type.</p>
<h5>Syntax:</h5>
<pre> [&lt;# elements&gt; x &lt;elementtype&gt;]<br></pre>
<pre>
[&lt;# elements&gt; x &lt;elementtype&gt;]
</pre>
<p>The number of elements is a constant integer value, elementtype may
be any type with a size.</p>
<h5>Examples:</h5>
<table class="layout">
<tr class="layout">
@ -756,34 +766,220 @@ be any integral or floating point type.</p>
</table>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="constants">Constants</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>LLVM has several different basic types of constants. This section describes
them all and their syntax.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="simpleconstants">Simple Constants</a>
</div>
<div class="doc_text">
<dl>
<dt><b>Boolean constants</b></dt>
<dd>The two strings '<tt>true</tt>' and '<tt>false</tt>' are both valid
constants of the <tt><a href="#t_primitive">bool</a></tt> type.
</dd>
<dt><b>Integer constants</b></dt>
<dd>Standard integers (such as '4') are constants of <a
href="#t_integer">integer</a> type. Negative numbers may be used with signed
integer types.
</dd>
<dt><b>Floating point constants</b></dt>
<dd>Floating point constants use standard decimal notation (e.g. 123.421),
exponential notation (e.g. 1.23421e+2), or a more precise hexadecimal
notation. etc. Floating point constants have an optional hexadecimal
notation (see below). Floating point constants must have a <a
href="#t_floating">floating point</a> type. </dd>
<dt><b>Null pointer constants</b></dt>
<dd>The identifier '<tt>null</tt>' is recognized as a null pointer constant,
and must be of <a href="#t_pointer">pointer type</a>.</dd>
</dl>
<p>The one non-intuitive notation for constants is the optional hexidecimal form
of floating point constants. For example, the form '<tt>double
0x432ff973cafa8000</tt>' is equivalent to (but harder to read than) '<tt>double
4.5e+15</tt>'. The only time hexadecimal floating point constants are required
(and the only time that they are generated by the disassembler) is when an FP
constant has to be emitted that is not representable as a decimal floating point
number exactly. For example, NaN's, infinities, and other special cases are
represented in their IEEE hexadecimal format so that assembly and disassembly do
not cause any bits to change in the constants.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="aggregateconstants">Aggregate Constants</a>
</div>
<div class="doc_text">
<dl>
<dt><b>Structure constants</b></dt>
<dd>Structure constants are represented with notation similar to structure
type definitions (a comma separated list of elements, surrounded by braces
(<tt>{}</tt>). For example: "<tt>{ int 4, float 17.0 }</tt>". Structure
constants must have <a href="#t_struct">structure type</a>, and the number and
types of elements must match those specified by the type.
</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 brackets
(<tt>[]</tt>). For example: "<tt>[ int 42, int 11, int 74 ]</tt>". Array
constants must have <a href="#t_array">array type</a>, and the number and
types of elements must match those specified by the type.
</dd>
<dt><b>Packed constants</b></dt>
<dd>Packed constants are represented with notation similar to packed type
definitions (a comma separated list of elements, surrounded by
less-than/greater-than's (<tt>&lt;&gt;</tt>). For example: "<tt>&lt; int 42,
int 11, int 74, int 100 &gt;</tt>". Packed constants must have <a
href="#t_packed">packed type</a>, and the number and types of elements must
match those specified by the type.
</dd>
<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.
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>
</dl>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="globalconstants">Global Variable and Function Addresses</a>
</div>
<div class="doc_text">
<p>The addresses of <a href="#globalvars">global variables</a> and <a
href="#functionstructure">functions</a> are always implicitly valid (link-time)
constants. These constants explicitly referenced when the <a
href="#identifiers">identifier for the global</a> is used, and always have <a
href="#t_pointer">pointer</a> type. For example, the following is a legal LLVM
file:</p>
<pre>
%X = global int 17
%Y = global int 42
%Z = global [2 x int*] [ int* %X, int* %Y ]
</pre>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="undefvalues">Undefined Values</a>
</div>
<div class="doc_text">
<p>The string '<tt>undef</tt>' is recognized as a filler that has no specified
value. Undefined values may be of any type, and be used anywhere a constant
is.</p>
<p>Undefined values are used to indicate the compiler that the program is well
defined no matter what value is used, giving it more freedom.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="constantexprs">Constant Expressions</a>
</div>
<div class="doc_text">
<p>Constant expressions are used to allow expressions involving other constants
to be used as constants. Constant expressions may be of any <a
href="#t_firstclass">first class</a> type, and may involve any LLVM operation
that does not have side effects (e.g. load and call are not supported). The
following is the syntax for constant expressions:</p>
<dl>
<dt><b><tt>cast ( CST to TYPE )</tt></b></dt>
<dd>Cast a constant to another type.</dd>
<dt><b><tt>getelementptr ( CSTPTR, IDX0, IDX1, ... )</tt></b></dt>
<dd>Perform the <a href="#i_getelementptr">getelementptr operation</a> on
constants. As with the <a href="#i_getelementptr">getelementptr</a>
instruction, the index list may have zero or more indexes, which are required
to make sense for the type of "CSTPTR".</dd>
<dt><b><tt>OPCODE ( LHS, RHS )</tt></b></dt>
<dd>Perform the specied operation of the LHS and RHS constants. OPCODE may be
any of the <a href="#binaryops">binary</a> or <a href="#bitwiseops">bitwise
binary</a> operations. The constraints on operands are the same as those for
the corresponding instruction (e.g. no bitwise operations on floating point
are allowed).</dd>
</dl>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"> <a name="instref">Instruction Reference</a> </div>
<!-- *********************************************************************** -->
<div class="doc_text">
<p>The LLVM instruction set consists of several different
classifications of instructions: <a href="#terminators">terminator
instructions</a>, <a href="#binaryops">binary instructions</a>, <a
href="#memoryops">memory instructions</a>, and <a href="#otherops">other
instructions</a>.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"> <a name="terminators">Terminator
Instructions</a> </div>
<div class="doc_text">
<p>As mentioned <a href="#functionstructure">previously</a>, every
basic block in a program ends with a "Terminator" instruction, which
indicates which block should be executed after the current block is
finished. These terminator instructions typically yield a '<tt>void</tt>'
value: they produce control flow, not values (the one exception being
the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction).</p>
<p>There are five different terminator instructions: the '<a
href="#i_ret"><tt>ret</tt></a>' instruction, the '<a href="#i_br"><tt>br</tt></a>'
instruction, the '<a href="#i_switch"><tt>switch</tt></a>' instruction,
the '<a href="#i_invoke"><tt>invoke</tt></a>' instruction, the '<a
href="#i_unwind"><tt>unwind</tt></a>' instruction, and the '<a
href="#i_unreachable"><tt>unreachable</tt></a>' instruction.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection"> <a name="i_ret">'<tt>ret</tt>'
Instruction</a> </div>
@ -2361,7 +2557,9 @@ unsigned 16 bit value, and the return value must be 8, 16, or 32 bits.
<h5>Syntax:</h5>
<pre>
call void (&lt;integer type&gt;, &lt;integer type&gt;)* %llvm.writeport (&lt;integer type&gt; &lt;value&gt;, &lt;integer type&gt; &lt;address&gt;)
call void (&lt;integer type&gt;, &lt;integer type&gt;)*
%llvm.writeport (&lt;integer type&gt; &lt;value&gt;,
&lt;integer type&gt; &lt;address&gt;)
</pre>
<h5>Overview:</h5>