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| author | Eric Botcazou <ebotcazou@adacore.com> | 2015-12-04 11:57:15 +0000 |
|---|---|---|
| committer | Eric Botcazou <ebotcazou@gcc.gnu.org> | 2015-12-04 11:57:15 +0000 |
| commit | 03c00798828246afcfd998988c9fee8321b9313c (patch) | |
| tree | d944ebe798474d59975ae0092d6818956e8aeba8 /gcc/doc | |
| parent | a3eb8a52b5c1e1f3af616d88bf6a057dd4f81eb3 (diff) | |
| download | gcc-03c00798828246afcfd998988c9fee8321b9313c.zip gcc-03c00798828246afcfd998988c9fee8321b9313c.tar.gz gcc-03c00798828246afcfd998988c9fee8321b9313c.tar.bz2 | |
re PR middle-end/65958 (-fstack-check breaks alloca on architectures using generic stack checking)
PR middle-end/65958
* gimplify.c (struct gimplify_ctx): Turn boolean fields into 1-bit
fields, add keep_stack and reorder them.
(gimplify_bind_expr): Save gimplify_ctxp->keep_stack on entry then
set it to false. Do not insert a stack save/restore pair if it has
been set to true by the gimplification of the statements.
Restore it to the saved value on exit if it is still false.
(gimplify_vla_decl): Do not set gimplify_ctxp->save_stack here.
(gimplify_call_expr) <BUILT_IN_ALLOCA[_WITH_ALIGN]>: New case. Set
either save_stack or keep_stack depending on CALL_ALLOCA_FOR_VAR_P.
* doc/extend.texi (Variable Length): Document new behavior.
* doc/generic.texi (Blocks): Document new handling of VLAs.
From-SVN: r231260
Diffstat (limited to 'gcc/doc')
| -rw-r--r-- | gcc/doc/extend.texi | 4 | ||||
| -rw-r--r-- | gcc/doc/generic.texi | 14 |
2 files changed, 10 insertions, 8 deletions
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index 63fce0f..6a5e2b8 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -1658,9 +1658,7 @@ variable-length arrays are more elegant. There are other differences between these two methods. Space allocated with @code{alloca} exists until the containing @emph{function} returns. The space for a variable-length array is deallocated as soon as the array -name's scope ends. (If you use both variable-length arrays and -@code{alloca} in the same function, deallocation of a variable-length array -also deallocates anything more recently allocated with @code{alloca}.) +name's scope ends, unless you also use @code{alloca} in this scope. You can also use variable-length arrays as arguments to functions: diff --git a/gcc/doc/generic.texi b/gcc/doc/generic.texi index bbafad9..f6b4397 100644 --- a/gcc/doc/generic.texi +++ b/gcc/doc/generic.texi @@ -1950,11 +1950,15 @@ this initialization replaces the @code{DECL_STMT}. These variables will never require cleanups. The scope of these variables is just the body -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}. This strategy -may change in the future. +Variable-length arrays (VLAs) complicate this process, as their size +often refers to variables initialized earlier in the block and their +initialization involves an explicit stack allocation. To handle this, +we add an indirection and replace them with a pointer to stack space +allocated by means of @code{alloca}. In most cases, we also arrange +for this space to be reclaimed when the enclosing @code{BIND_EXPR} is +exited, the exception to this being when there is an explicit call to +@code{alloca} in the source code, in which case the stack is left +depressed on exit of the @code{BIND_EXPR}. A C++ program will usually contain more @code{BIND_EXPR}s than there are syntactic blocks in the source code, since several C++ |