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150 lines
7.3 KiB
HTML
150 lines
7.3 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Basic Statements - GNU Compiler Collection (GCC) Internals</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Statements.html#Statements" title="Statements">
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<link rel="next" href="Blocks.html#Blocks" title="Blocks">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Basic-Statements"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Blocks.html#Blocks">Blocks</a>,
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Up: <a rel="up" accesskey="u" href="Statements.html#Statements">Statements</a>
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<hr>
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</div>
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<h4 class="subsection">10.7.1 Basic Statements</h4>
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<p><a name="index-Basic-Statements-1937"></a>
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<dl>
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<dt><code>ASM_EXPR</code><dd>
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Used to represent an inline assembly statement. For an inline assembly
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statement like:
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<pre class="smallexample"> asm ("mov x, y");
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</pre>
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<p>The <code>ASM_STRING</code> macro will return a <code>STRING_CST</code> node for
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<code>"mov x, y"</code>. If the original statement made use of the
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extended-assembly syntax, then <code>ASM_OUTPUTS</code>,
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<code>ASM_INPUTS</code>, and <code>ASM_CLOBBERS</code> will be the outputs, inputs,
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and clobbers for the statement, represented as <code>STRING_CST</code> nodes.
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The extended-assembly syntax looks like:
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<pre class="smallexample"> asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
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</pre>
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<p>The first string is the <code>ASM_STRING</code>, containing the instruction
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template. The next two strings are the output and inputs, respectively;
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this statement has no clobbers. As this example indicates, “plain”
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assembly statements are merely a special case of extended assembly
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statements; they have no cv-qualifiers, outputs, inputs, or clobbers.
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All of the strings will be <code>NUL</code>-terminated, and will contain no
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embedded <code>NUL</code>-characters.
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<p>If the assembly statement is declared <code>volatile</code>, or if the
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statement was not an extended assembly statement, and is therefore
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implicitly volatile, then the predicate <code>ASM_VOLATILE_P</code> will hold
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of the <code>ASM_EXPR</code>.
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<br><dt><code>DECL_EXPR</code><dd>
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Used to represent a local declaration. The <code>DECL_EXPR_DECL</code> macro
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can be used to obtain the entity declared. This declaration may be a
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<code>LABEL_DECL</code>, indicating that the label declared is a local label.
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(As an extension, GCC allows the declaration of labels with scope.) In
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C, this declaration may be a <code>FUNCTION_DECL</code>, indicating the
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use of the GCC nested function extension. For more information,
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see <a href="Functions.html#Functions">Functions</a>.
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<br><dt><code>LABEL_EXPR</code><dd>
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Used to represent a label. The <code>LABEL_DECL</code> declared by this
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statement can be obtained with the <code>LABEL_EXPR_LABEL</code> macro. The
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<code>IDENTIFIER_NODE</code> giving the name of the label can be obtained from
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the <code>LABEL_DECL</code> with <code>DECL_NAME</code>.
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<br><dt><code>GOTO_EXPR</code><dd>
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Used to represent a <code>goto</code> statement. The <code>GOTO_DESTINATION</code> will
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usually be a <code>LABEL_DECL</code>. However, if the “computed goto” extension
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has been used, the <code>GOTO_DESTINATION</code> will be an arbitrary expression
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indicating the destination. This expression will always have pointer type.
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<br><dt><code>RETURN_EXPR</code><dd>
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Used to represent a <code>return</code> statement. Operand 0 represents the
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value to return. It should either be the <code>RESULT_DECL</code> for the
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containing function, or a <code>MODIFY_EXPR</code> or <code>INIT_EXPR</code>
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setting the function's <code>RESULT_DECL</code>. It will be
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<code>NULL_TREE</code> if the statement was just
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<pre class="smallexample"> return;
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</pre>
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<br><dt><code>LOOP_EXPR</code><dd>These nodes represent “infinite” loops. The <code>LOOP_EXPR_BODY</code>
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represents the body of the loop. It should be executed forever, unless
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an <code>EXIT_EXPR</code> is encountered.
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<br><dt><code>EXIT_EXPR</code><dd>These nodes represent conditional exits from the nearest enclosing
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<code>LOOP_EXPR</code>. The single operand is the condition; if it is
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nonzero, then the loop should be exited. An <code>EXIT_EXPR</code> will only
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appear within a <code>LOOP_EXPR</code>.
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<br><dt><code>SWITCH_STMT</code><dd>
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Used to represent a <code>switch</code> statement. The <code>SWITCH_STMT_COND</code>
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is the expression on which the switch is occurring. See the documentation
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for an <code>IF_STMT</code> for more information on the representation used
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for the condition. The <code>SWITCH_STMT_BODY</code> is the body of the switch
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statement. The <code>SWITCH_STMT_TYPE</code> is the original type of switch
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expression as given in the source, before any compiler conversions.
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<br><dt><code>CASE_LABEL_EXPR</code><dd>
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Use to represent a <code>case</code> label, range of <code>case</code> labels, or a
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<code>default</code> label. If <code>CASE_LOW</code> is <code>NULL_TREE</code>, then this is a
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<code>default</code> label. Otherwise, if <code>CASE_HIGH</code> is <code>NULL_TREE</code>, then
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this is an ordinary <code>case</code> label. In this case, <code>CASE_LOW</code> is
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an expression giving the value of the label. Both <code>CASE_LOW</code> and
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<code>CASE_HIGH</code> are <code>INTEGER_CST</code> nodes. These values will have
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the same type as the condition expression in the switch statement.
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<p>Otherwise, if both <code>CASE_LOW</code> and <code>CASE_HIGH</code> are defined, the
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statement is a range of case labels. Such statements originate with the
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extension that allows users to write things of the form:
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<pre class="smallexample"> case 2 ... 5:
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</pre>
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<p>The first value will be <code>CASE_LOW</code>, while the second will be
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<code>CASE_HIGH</code>.
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</dl>
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</body></html>
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