Protect some checks of DECL_FUNCTION_CODE

Protect some checks of DECL_FUNCTION_CODE

This patch protects various uses of DECL_FUNCTION_CODE that didn't
obviously check for BUILT_IN_NORMAL first (either directly or in callers).
They could therefore trigger for functions that either aren't built-ins
or are a different kind of built-in.

Also, the patch removes a redundant GIMPLE_CALL check from
optimize_stdarg_builtin, since it gave the impression that the stmt
was less well checked than it actually is.

2019-08-13  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR middle-end/91421
	* attribs.c (decl_attributes): Check the DECL_BUILT_IN_CLASS
	before the DECL_FUNCTION_CODE.
	* calls.c (maybe_warn_alloc_args_overflow): Use fndecl_built_in_p
	to check for a BUILT_IN_ALLOCA call.
	* ipa-cp.c (ipa_get_indirect_edge_target_1): Likewise for
	BUILT_IN_UNREACHABLE.  Don't check for a FUNCTION_TYPE.
	* ipa-devirt.c (possible_polymorphic_call_target_p): Likewise.
	* ipa-prop.c (try_make_edge_direct_virtual_call): Likewise.
	* gimple-ssa-isolate-paths.c (is_addr_local): Check specifically
	for BUILT_IN_NORMAL functions.
	* trans-mem.c (expand_block_edges): Use gimple_call_builtin_p to
	test for BUILT_IN_TM_ABORT.
	* tree-ssa-ccp.c (optimize_stack_restore): Use fndecl_built_in_p
	to check for a BUILT_IN_STACK_RESTORE call.
	(optimize_stdarg_builtin): Remove redundant check for GIMPLE_CALL.
	* tree-ssa-threadedge.c
	(record_temporary_equivalences_from_stmts_at_dest): Check for a
	BUILT_IN_NORMAL decl before checking its DECL_FUNCTION_CODE.
	* tree-vect-patterns.c (vect_recog_pow_pattern): Use a positive
	test for a BUILT_IN_NORMAL call instead of a negative test for
	an internal function call.

gcc/c/
	PR middle-end/91421
	* c-decl.c (header_for_builtin_fn): Take a FUNCTION_DECL instead
	of a built_in_function.
	(diagnose_mismatched_decls, implicitly_declare): Update accordingly.

From-SVN: r274403