re PR middle-end/20548 (ACATS c52103x c52104x c52104y segfault)

	PR ada/20548
	* common.opt (-fstack-check): Do not declare the variable here.
	(-fstack-check=): New option variant.
	* doc/invoke.texi (Code Gen Options): Document it.
	* expr.h (STACK_OLD_CHECK_PROTECT): New macro.
	(STACK_CHECK_PROTECT): Bump to 3 pages if DWARF-2 EH is used.
	(STACK_CHECK_STATIC_BUILTIN): New macro.
	* doc/tm.texi (Stack Checking): Document STACK_CHECK_STATIC_BUILTIN.
	* opts.c: Include expr.h.
	(common_handle_option) <OPT_fold_stack_check_>: New case.
	<OPT_fstack_check>: Likewise.
	* calls.c (initialize_argument_information): Use TYPE_SIZE_UNIT
	consistently in the test for variable-sized types.  Adjust for
	new behaviour of flag_stack_check.
	* explow.c: Include except.h.
	(allocate_dynamic_stack_space): Do not take into account
	STACK_CHECK_MAX_FRAME_SIZE for static builtin stack checking.
	* function.c (gimplify_parameters): Use DECL_SIZE_UNIT in the test
	for variable-sized parameters.  Treat all parameters whose size is
	greater than STACK_CHECK_MAX_VAR_SIZE as variable-sized if generic
	stack checking is enabled.
	* gimplify.c (gimplify_decl_expr): Treat non-static objects whose
	size is greater than STACK_CHECK_MAX_VAR_SIZE as variable-sized
	if generic stack checking is enabled.
	(expand_function_end): Adjust for new behaviour of flag_stack_check.
	* reload1.c (reload): Likewise.
	* stmt.c (expand_decl): Assert that all automatic variables have
	fixed size at this point and remove dead code.
	* flags.h (stack_check_type): New enumeration type.
	(flag_stack_check): Declare.
	* toplev.c (flag_stack_check): New global variable.
	* Makefile.in (opts.o): Add dependency on EXPR_H.
	(explow.o): Add dependency on except.h.
ada/
	* gcc-interface/decl.c (gnat_to_gnu_entity): Use DECL_SIZE_UNIT in the
	setjmp test consistently.  Adjust for new behaviour of flag_stack_check.
	* gcc-interface/utils2.c (build_call_alloc_dealloc): Remove redundant
	test of flag_stack_check.  Adjust for new behaviour of flag_stack_check.

From-SVN: r139159

2 files changed, 60 insertions, 19 deletions

diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 56a0bda..40c3df1 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -15207,8 +15207,34 @@ a single-threaded environment since stack overflow is automatically
 detected on nearly all systems if there is only one stack.
 
 Note that this switch does not actually cause checking to be done; the
-operating system must do that.  The switch causes generation of code
-to ensure that the operating system sees the stack being extended.
+operating system or the language runtime must do that.  The switch causes
+generation of code to ensure that they see the stack being extended.
+
+You can additionally specify a string parameter: @code{no} means no
+checking, @code{generic} means force the use of old-style checking,
+@code{specific} means use the best checking method and is equivalent
+to bare @option{-fstack-check}.
+
+Old-style checking is a generic mechanism that requires no specific
+target support in the compiler but comes with the following drawbacks:
+
+@enumerate
+@item
+Modified allocation strategy for large objects: they will always be
+allocated dynamically if their size exceeds a fixed threshold.
+
+@item
+Fixed limit on the size of the static frame of functions: when it is
+topped by a particular function, stack checking is not reliable and
+a warning is issued by the compiler.
+
+@item
+Inefficiency: because of both the modified allocation strategy and the
+generic implementation, the performances of the code are hampered.
+@end enumerate
+
+Note that old-style stack checking is also the fallback method for
+@code{specific} if no target support has been added in the compiler.
 
 @item -fstack-limit-register=@var{reg}
 @itemx -fstack-limit-symbol=@var{sym}
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 5decc33..9b4a921 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -3376,38 +3376,49 @@ linkage is necessary.  The default is @code{0}.
 @node Stack Checking
 @subsection Specifying How Stack Checking is Done
 
-GCC will check that stack references are within the boundaries of
-the stack, if the @option{-fstack-check} is specified, in one of three ways:
+GCC will check that stack references are within the boundaries of the
+stack, if the option @option{-fstack-check} is specified, in one of
+three ways:
 
 @enumerate
 @item
 If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC
-will assume that you have arranged for stack checking to be done at
-appropriate places in the configuration files, e.g., in
-@code{TARGET_ASM_FUNCTION_PROLOGUE}.  GCC will do not other special
-processing.
+will assume that you have arranged for full stack checking to be done
+at appropriate places in the configuration files.  GCC will not do
+other special processing.
 
 @item
-If @code{STACK_CHECK_BUILTIN} is zero and you defined a named pattern
-called @code{check_stack} in your @file{md} file, GCC will call that
-pattern with one argument which is the address to compare the stack
-value against.  You must arrange for this pattern to report an error if
-the stack pointer is out of range.
+If @code{STACK_CHECK_BUILTIN} is zero and the value of the
+@code{STACK_CHECK_STATIC_BUILTIN} macro is nonzero, GCC will assume
+that you have arranged for static stack checking (checking of the
+static stack frame of functions) to be done at appropriate places
+in the configuration files.  GCC will only emit code to do dynamic
+stack checking (checking on dynamic stack allocations) using the third
+approach below.
 
 @item
 If neither of the above are true, GCC will generate code to periodically
 ``probe'' the stack pointer using the values of the macros defined below.
 @end enumerate
 
-Normally, you will use the default values of these macros, so GCC
-will use the third approach.
+If neither STACK_CHECK_BUILTIN nor STACK_CHECK_STATIC_BUILTIN is defined,
+GCC will change its allocation strategy for large objects if the option
+@option{-fstack-check} is specified: they will always be allocated
+dynamically if their size exceeds @code{STACK_CHECK_MAX_VAR_SIZE} bytes.
 
 @defmac STACK_CHECK_BUILTIN
 A nonzero value if stack checking is done by the configuration files in a
 machine-dependent manner.  You should define this macro if stack checking
-is require by the ABI of your machine or if you would like to have to stack
-checking in some more efficient way than GCC's portable approach.
-The default value of this macro is zero.
+is require by the ABI of your machine or if you would like to do stack
+checking in some more efficient way than the generic approach.  The default
+value of this macro is zero.
+@end defmac
+
+@defmac STACK_CHECK_STATIC_BUILTIN
+A nonzero value if static stack checking is done by the configuration files
+in a machine-dependent manner.  You should define this macro if you would
+like to do static stack checking in some more efficient way than the generic
+approach.  The default value of this macro is zero.
 @end defmac
 
 @defmac STACK_CHECK_PROBE_INTERVAL
@@ -3418,7 +3429,7 @@ default value of 4096 is suitable for most systems.
 @end defmac
 
 @defmac STACK_CHECK_PROBE_LOAD
-A integer which is nonzero if GCC should perform the stack probe
+An integer which is nonzero if GCC should perform the stack probe
 as a load instruction and zero if GCC should use a store instruction.
 The default is zero, which is the most efficient choice on most systems.
 @end defmac
@@ -3429,6 +3440,10 @@ for languages where such a recovery is supported.  The default value of
 75 words should be adequate for most machines.
 @end defmac
 
+The following macros are relevant only if neither STACK_CHECK_BUILTIN
+nor STACK_CHECK_STATIC_BUILTIN is defined; you can omit them altogether
+in the opposite case.
+
 @defmac STACK_CHECK_MAX_FRAME_SIZE
 The maximum size of a stack frame, in bytes.  GCC will generate probe
 instructions in non-leaf functions to ensure at least this many bytes of