308 lines
13 KiB
HTML
308 lines
13 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
|
<html>
|
|
<!-- Copyright (C) 1988-2016 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with the
|
|
Invariant Sections being "Funding Free Software", the Front-Cover
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
|
(see below). A copy of the license is included in the section entitled
|
|
"GNU Free Documentation License".
|
|
|
|
(a) The FSF's Front-Cover Text is:
|
|
|
|
A GNU Manual
|
|
|
|
(b) The FSF's Back-Cover Text is:
|
|
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
|
software. Copies published by the Free Software Foundation raise
|
|
funds for GNU development. -->
|
|
<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<title>GNU Compiler Collection (GCC) Internals: Logical Operators</title>
|
|
|
|
<meta name="description" content="GNU Compiler Collection (GCC) Internals: Logical Operators">
|
|
<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Logical Operators">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content="makeinfo">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<link href="index.html#Top" rel="start" title="Top">
|
|
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Operands.html#Operands" rel="up" title="Operands">
|
|
<link href="Manipulating-GIMPLE-statements.html#Manipulating-GIMPLE-statements" rel="next" title="Manipulating GIMPLE statements">
|
|
<link href="Conditional-Expressions.html#Conditional-Expressions" rel="prev" title="Conditional Expressions">
|
|
<style type="text/css">
|
|
<!--
|
|
a.summary-letter {text-decoration: none}
|
|
blockquote.smallquotation {font-size: smaller}
|
|
div.display {margin-left: 3.2em}
|
|
div.example {margin-left: 3.2em}
|
|
div.indentedblock {margin-left: 3.2em}
|
|
div.lisp {margin-left: 3.2em}
|
|
div.smalldisplay {margin-left: 3.2em}
|
|
div.smallexample {margin-left: 3.2em}
|
|
div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
|
|
div.smalllisp {margin-left: 3.2em}
|
|
kbd {font-style:oblique}
|
|
pre.display {font-family: inherit}
|
|
pre.format {font-family: inherit}
|
|
pre.menu-comment {font-family: serif}
|
|
pre.menu-preformatted {font-family: serif}
|
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
|
pre.smallexample {font-size: smaller}
|
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
|
pre.smalllisp {font-size: smaller}
|
|
span.nocodebreak {white-space:nowrap}
|
|
span.nolinebreak {white-space:nowrap}
|
|
span.roman {font-family:serif; font-weight:normal}
|
|
span.sansserif {font-family:sans-serif; font-weight:normal}
|
|
ul.no-bullet {list-style: none}
|
|
-->
|
|
</style>
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
|
|
<a name="Logical-Operators"></a>
|
|
<div class="header">
|
|
<p>
|
|
Previous: <a href="Conditional-Expressions.html#Conditional-Expressions" accesskey="p" rel="prev">Conditional Expressions</a>, Up: <a href="Operands.html#Operands" accesskey="u" rel="up">Operands</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<a name="Logical-Operators-1"></a>
|
|
<h4 class="subsection">11.6.4 Logical Operators</h4>
|
|
<a name="index-Logical-Operators"></a>
|
|
|
|
<p>Except when they appear in the condition operand of a
|
|
<code>GIMPLE_COND</code>, logical ‘and’ and ‘or’ operators are simplified
|
|
as follows: <code>a = b && c</code> becomes
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">T1 = (bool)b;
|
|
if (T1 == true)
|
|
T1 = (bool)c;
|
|
a = T1;
|
|
</pre></div>
|
|
|
|
<p>Note that <code>T1</code> in this example cannot be an expression temporary,
|
|
because it has two different assignments.
|
|
</p>
|
|
<a name="Manipulating-operands"></a>
|
|
<h4 class="subsection">11.6.5 Manipulating operands</h4>
|
|
|
|
<p>All gimple operands are of type <code>tree</code>. But only certain
|
|
types of trees are allowed to be used as operand tuples. Basic
|
|
validation is controlled by the function
|
|
<code>get_gimple_rhs_class</code>, which given a tree code, returns an
|
|
<code>enum</code> with the following values of type <code>enum
|
|
gimple_rhs_class</code>
|
|
</p>
|
|
<ul>
|
|
<li> <code>GIMPLE_INVALID_RHS</code>
|
|
The tree cannot be used as a GIMPLE operand.
|
|
|
|
</li><li> <code>GIMPLE_TERNARY_RHS</code>
|
|
The tree is a valid GIMPLE ternary operation.
|
|
|
|
</li><li> <code>GIMPLE_BINARY_RHS</code>
|
|
The tree is a valid GIMPLE binary operation.
|
|
|
|
</li><li> <code>GIMPLE_UNARY_RHS</code>
|
|
The tree is a valid GIMPLE unary operation.
|
|
|
|
</li><li> <code>GIMPLE_SINGLE_RHS</code>
|
|
The tree is a single object, that cannot be split into simpler
|
|
operands (for instance, <code>SSA_NAME</code>, <code>VAR_DECL</code>, <code>COMPONENT_REF</code>, etc).
|
|
|
|
<p>This operand class also acts as an escape hatch for tree nodes
|
|
that may be flattened out into the operand vector, but would need
|
|
more than two slots on the RHS. For instance, a <code>COND_EXPR</code>
|
|
expression of the form <code>(a op b) ? x : y</code> could be flattened
|
|
out on the operand vector using 4 slots, but it would also
|
|
require additional processing to distinguish <code>c = a op b</code>
|
|
from <code>c = a op b ? x : y</code>. Something similar occurs with
|
|
<code>ASSERT_EXPR</code>. In time, these special case tree
|
|
expressions should be flattened into the operand vector.
|
|
</p></li></ul>
|
|
|
|
<p>For tree nodes in the categories <code>GIMPLE_TERNARY_RHS</code>,
|
|
<code>GIMPLE_BINARY_RHS</code> and <code>GIMPLE_UNARY_RHS</code>, they cannot be
|
|
stored inside tuples directly. They first need to be flattened and
|
|
separated into individual components. For instance, given the GENERIC
|
|
expression
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">a = b + c
|
|
</pre></div>
|
|
|
|
<p>its tree representation is:
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">MODIFY_EXPR <VAR_DECL <a>, PLUS_EXPR <VAR_DECL <b>, VAR_DECL <c>>>
|
|
</pre></div>
|
|
|
|
<p>In this case, the GIMPLE form for this statement is logically
|
|
identical to its GENERIC form but in GIMPLE, the <code>PLUS_EXPR</code>
|
|
on the RHS of the assignment is not represented as a tree,
|
|
instead the two operands are taken out of the <code>PLUS_EXPR</code> sub-tree
|
|
and flattened into the GIMPLE tuple as follows:
|
|
</p>
|
|
<div class="smallexample">
|
|
<pre class="smallexample">GIMPLE_ASSIGN <PLUS_EXPR, VAR_DECL <a>, VAR_DECL <b>, VAR_DECL <c>>
|
|
</pre></div>
|
|
|
|
<a name="Operand-vector-allocation"></a>
|
|
<h4 class="subsection">11.6.6 Operand vector allocation</h4>
|
|
|
|
<p>The operand vector is stored at the bottom of the three tuple
|
|
structures that accept operands. This means, that depending on
|
|
the code of a given statement, its operand vector will be at
|
|
different offsets from the base of the structure. To access
|
|
tuple operands use the following accessors
|
|
</p>
|
|
<dl>
|
|
<dt><a name="index-gimple_005fnum_005fops"></a>GIMPLE function: <em>unsigned</em> <strong>gimple_num_ops</strong> <em>(gimple g)</em></dt>
|
|
<dd><p>Returns the number of operands in statement G.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-gimple_005fop"></a>GIMPLE function: <em>tree</em> <strong>gimple_op</strong> <em>(gimple g, unsigned i)</em></dt>
|
|
<dd><p>Returns operand <code>I</code> from statement <code>G</code>.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-gimple_005fops"></a>GIMPLE function: <em>tree *</em> <strong>gimple_ops</strong> <em>(gimple g)</em></dt>
|
|
<dd><p>Returns a pointer into the operand vector for statement <code>G</code>. This
|
|
is computed using an internal table called <code>gimple_ops_offset_</code>[].
|
|
This table is indexed by the gimple code of <code>G</code>.
|
|
</p>
|
|
<p>When the compiler is built, this table is filled-in using the
|
|
sizes of the structures used by each statement code defined in
|
|
gimple.def. Since the operand vector is at the bottom of the
|
|
structure, for a gimple code <code>C</code> the offset is computed as sizeof
|
|
(struct-of <code>C</code>) - sizeof (tree).
|
|
</p>
|
|
<p>This mechanism adds one memory indirection to every access when
|
|
using <code>gimple_op</code>(), if this becomes a bottleneck, a pass can
|
|
choose to memoize the result from <code>gimple_ops</code>() and use that to
|
|
access the operands.
|
|
</p></dd></dl>
|
|
|
|
<a name="Operand-validation"></a>
|
|
<h4 class="subsection">11.6.7 Operand validation</h4>
|
|
|
|
<p>When adding a new operand to a gimple statement, the operand will
|
|
be validated according to what each tuple accepts in its operand
|
|
vector. These predicates are called by the
|
|
<code>gimple_<var>name</var>_set_...()</code>. Each tuple will use one of the
|
|
following predicates (Note, this list is not exhaustive):
|
|
</p>
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fval"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_val</strong> <em>(tree t)</em></dt>
|
|
<dd><p>Returns true if t is a "GIMPLE value", which are all the
|
|
non-addressable stack variables (variables for which
|
|
<code>is_gimple_reg</code> returns true) and constants (expressions for which
|
|
<code>is_gimple_min_invariant</code> returns true).
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005faddressable"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_addressable</strong> <em>(tree t)</em></dt>
|
|
<dd><p>Returns true if t is a symbol or memory reference whose address
|
|
can be taken.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fasm_005fval"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_asm_val</strong> <em>(tree t)</em></dt>
|
|
<dd><p>Similar to <code>is_gimple_val</code> but it also accepts hard registers.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fcall_005faddr"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_call_addr</strong> <em>(tree t)</em></dt>
|
|
<dd><p>Return true if t is a valid expression to use as the function
|
|
called by a <code>GIMPLE_CALL</code>.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fmem_005fref_005faddr"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_mem_ref_addr</strong> <em>(tree t)</em></dt>
|
|
<dd><p>Return true if t is a valid expression to use as first operand
|
|
of a <code>MEM_REF</code> expression.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fconstant"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_constant</strong> <em>(tree t)</em></dt>
|
|
<dd><p>Return true if t is a valid gimple constant.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fmin_005finvariant"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_min_invariant</strong> <em>(tree t)</em></dt>
|
|
<dd><p>Return true if t is a valid minimal invariant. This is different
|
|
from constants, in that the specific value of t may not be known
|
|
at compile time, but it is known that it doesn’t change (e.g.,
|
|
the address of a function local variable).
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fip_005finvariant"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_ip_invariant</strong> <em>(tree t)</em></dt>
|
|
<dd><p>Return true if t is an interprocedural invariant. This means that t
|
|
is a valid invariant in all functions (e.g. it can be an address of a
|
|
global variable but not of a local one).
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fip_005finvariant_005faddress"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_ip_invariant_address</strong> <em>(tree t)</em></dt>
|
|
<dd><p>Return true if t is an <code>ADDR_EXPR</code> that does not change once the
|
|
program is running (and which is valid in all functions).
|
|
</p></dd></dl>
|
|
|
|
|
|
<a name="Statement-validation"></a>
|
|
<h4 class="subsection">11.6.8 Statement validation</h4>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fassign"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_assign</strong> <em>(gimple g)</em></dt>
|
|
<dd><p>Return true if the code of g is <code>GIMPLE_ASSIGN</code>.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fcall"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_call</strong> <em>(gimple g)</em></dt>
|
|
<dd><p>Return true if the code of g is <code>GIMPLE_CALL</code>.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fdebug"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_debug</strong> <em>(gimple g)</em></dt>
|
|
<dd><p>Return true if the code of g is <code>GIMPLE_DEBUG</code>.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-gimple_005fassign_005fcast_005fp"></a>GIMPLE function: <em>bool</em> <strong>gimple_assign_cast_p</strong> <em>(const_gimple g)</em></dt>
|
|
<dd><p>Return true if g is a <code>GIMPLE_ASSIGN</code> that performs a type cast
|
|
operation.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-gimple_005fdebug_005fbind_005fp"></a>GIMPLE function: <em>bool</em> <strong>gimple_debug_bind_p</strong> <em>(gimple g)</em></dt>
|
|
<dd><p>Return true if g is a <code>GIMPLE_DEBUG</code> that binds the value of an
|
|
expression to a variable.
|
|
</p></dd></dl>
|
|
|
|
<dl>
|
|
<dt><a name="index-is_005fgimple_005fomp"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_omp</strong> <em>(gimple g)</em></dt>
|
|
<dd><p>Return true if g is any of the OpenMP codes.
|
|
</p></dd></dl>
|
|
|
|
<hr>
|
|
<div class="header">
|
|
<p>
|
|
Previous: <a href="Conditional-Expressions.html#Conditional-Expressions" accesskey="p" rel="prev">Conditional Expressions</a>, Up: <a href="Operands.html#Operands" accesskey="u" rel="up">Operands</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|