PR c/81544 - attribute noreturn and warn_unused_result on the same function accepted

PR c/81544 - attribute noreturn and warn_unused_result on the same function accepted
PR c/81566 - invalid attribute aligned accepted on functions

gcc/ada/ChangeLog:

	PR c/81544
	* gcc-interface/utils.c (gnat_internal_attribute_table): Initialize
	new member of struct attribute_spec.

gcc/c/ChangeLog:

	PR c/81544
	* c-decl.c (c_decl_attributes): Look up existing declaration and
	pass it to decl_attributes.

gcc/c-family/ChangeLog:

	PR c/81544
	PR c/81566
	* c-attribs.c (attr_aligned_exclusions): New array.
	(attr_alloc_exclusions, attr_cold_hot_exclusions): Same.
	(attr_common_exclusions, attr_const_pure_exclusions): Same.
	(attr_gnu_inline_exclusions, attr_inline_exclusions): Same.
	(attr_noreturn_exclusions, attr_returns_twice_exclusions): Same.
	(attr_warn_unused_result_exclusions): Same.
	(handle_hot_attribute, handle_cold_attribute): Simplify.
	(handle_const_attribute): Warn on function returning void.
	(handle_pure_attribute): Same.
	(handle_aligned_attribute): Diagnose conflicting attribute
	specifications.
	* c-warn.c (diagnose_mismatched_attributes): Simplify.

gcc/cp/ChangeLog:

	PR c/81544
	* cp-tree.h (decls_match): Add default argument.
	* decl.c (decls_match): Avoid calling into the target back end
	and triggering an error.
	* decl2.c (cplus_decl_attributes): Look up existing declaration and
	pass it to decl_attributes.
	* tree.c (cxx_attribute_table): Initialize new member of struct
	attribute_spec.

gcc/fortran/ChangeLog:

	PR c/81544
	* f95-lang.c (gfc_attribute_table): Initialize new member of struct
	attribute_spec.

gcc/lto/ChangeLog:

	PR c/81544
	* lto-lang.c (lto_attribute_table): Initialize new member of struct
	attribute_spec.

gcc/ChangeLog:

	PR c/81544
	* attribs.c (empty_attribute_table): Initialize new member of
	struct attribute_spec.
	(decl_attributes): Add argument.  Handle mutually exclusive
	combinations of attributes.
	(selftests::test_attribute_exclusions): New function.
	(selftests::attribute_c_tests): Ditto.
	* attribs.h (decl_attributes): Add default argument.
	* selftest.h (attribute_c_tests): Declare.
	* selftest-run-tests.c (selftest::run_tests): Call attribute_c_tests.
	* tree-core.h (attribute_spec::exclusions, exclude): New type and
	member.
	* doc/extend.texi (Common Function Attributes): Update const and pure.

gcc/testsuite/ChangeLog:

	PR c/81544
	* c-c++-common/Wattributes-2.c: New test.
	* c-c++-common/Wattributes.c: New test.
	* c-c++-common/attributes-3.c: Adjust.
	* gcc.dg/Wattributes-6.c: New test.
	* gcc.dg/Wattributes-7.c: New test.
	* gcc.dg/attr-noinline.c
	* gcc.dg/pr44964.c: Same.
	* gcc.dg/torture/pr42363.c: Same.
	* gcc.dg/tree-ssa/ssa-ccp-2.c: Same.

From-SVN: r255469

1 files changed, 14 insertions, 4 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 3d5e15c..ad4d9d3 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -2493,9 +2493,14 @@ are automatically detected and this attribute is ignored.
 @cindex @code{const} function attribute
 @cindex functions that have no side effects
 Many functions do not examine any values except their arguments, and
-have no effects except the return value.  Basically this is just slightly
-more strict class than the @code{pure} attribute below, since function is not
-allowed to read global memory.
+have no effects except to return a value.  Calls to such functions lend
+themselves to optimization such as common subexpression elimination.
+The @code{const} attribute imposes greater restrictions on a function's
+definition than the similar @code{pure} attribute below because it prohibits
+the function from reading global variables.  Consequently, the presence of
+the attribute on a function declarations allows GCC to emit more efficient
+code for some calls to the function.  Decorating the same function with
+both the @code{const} and the @code{pure} attribute is diagnnosed.
 
 @cindex pointer arguments
 Note that a function that has pointer arguments and examines the data
@@ -3190,7 +3195,7 @@ to prevent recursion.
 @cindex functions that have no side effects
 Many functions have no effects except the return value and their
 return value depends only on the parameters and/or global variables.
-Such a function can be subject
+Calls to such functions can be subject
 to common subexpression elimination and loop optimization just as an
 arithmetic operator would be.  These functions should be declared
 with the attribute @code{pure}.  For example,
@@ -3208,6 +3213,11 @@ Interesting non-pure functions are functions with infinite loops or those
 depending on volatile memory or other system resource, that may change between
 two consecutive calls (such as @code{feof} in a multithreading environment).
 
+The @code{pure} attribute imposes similar but looser restrictions on
+a function's defintion than the @code{const} attribute: it allows the
+function to read global variables.  Decorating the same function with
+both the @code{pure} and the @code{const} attribute is diagnosed.
+
 @item returns_nonnull
 @cindex @code{returns_nonnull} function attribute
 The @code{returns_nonnull} attribute specifies that the function