10.2.4.1 Blocks

Block scopes and the variables they declare in GENERIC and GIMPLE are expressed using the BIND_EXPR code, which in previous versions of GCC was primarily used for the C statement-expression extension.

Variables in a block are collected into BIND_EXPR_VARS in declaration order. Any runtime initialization is moved out of DECL_INITIAL and into a statement in the controlled block. When gimplifying from C or C++, this initialization replaces the DECL_STMT.

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 BIND_EXPR. This strategy may change in the future.

DECL_SAVED_TREE for a GIMPLE function will always be a BIND_EXPR which contains declarations for the temporary variables used in the function.

A C++ program will usually contain more BIND_EXPRs 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 BIND_EXPR.