| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- Copyright (C) 1988-2015 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: Blocks</title> |
| |
| <meta name="description" content="GNU Compiler Collection (GCC) Internals: Blocks"> |
| <meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Blocks"> |
| <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="Statements.html#Statements" rel="up" title="Statements"> |
| <link href="Statement-Sequences.html#Statement-Sequences" rel="next" title="Statement Sequences"> |
| <link href="Basic-Statements.html#Basic-Statements" rel="prev" title="Basic Statements"> |
| <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="Blocks"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Statement-Sequences.html#Statement-Sequences" accesskey="n" rel="next">Statement Sequences</a>, Previous: <a href="Basic-Statements.html#Basic-Statements" accesskey="p" rel="prev">Basic Statements</a>, Up: <a href="Statements.html#Statements" accesskey="u" rel="up">Statements</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="Blocks-1"></a> |
| <h4 class="subsection">10.7.2 Blocks</h4> |
| <a name="index-Blocks"></a> |
| |
| <p>Block scopes and the variables they declare in GENERIC are |
| expressed using the <code>BIND_EXPR</code> code, which in previous |
| versions of GCC was primarily used for the C statement-expression |
| extension. |
| </p> |
| <p>Variables in a block are collected into <code>BIND_EXPR_VARS</code> in |
| declaration order through their <code>TREE_CHAIN</code> field. Any runtime |
| initialization is moved out of <code>DECL_INITIAL</code> and into a |
| statement in the controlled block. When gimplifying from C or C++, |
| this initialization replaces the <code>DECL_STMT</code>. These variables |
| will never require cleanups. The scope of these variables is just the |
| body |
| </p> |
| <p>Variable-length arrays (VLAs) complicate this process, as their |
| size often refers to variables initialized earlier in the block. |
| To handle this, we currently split the block at that point, and |
| move the VLA into a new, inner <code>BIND_EXPR</code>. This strategy |
| may change in the future. |
| </p> |
| <p>A C++ program will usually contain more <code>BIND_EXPR</code>s than |
| there are syntactic blocks in the source code, since several C++ |
| constructs have implicit scopes associated with them. On the |
| other hand, although the C++ front end uses pseudo-scopes to |
| handle cleanups for objects with destructors, these don’t |
| translate into the GIMPLE form; multiple declarations at the same |
| level use the same <code>BIND_EXPR</code>. |
| </p> |
| |
| |
| |
| </body> |
| </html> |
