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| <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>. |
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