Fix bugs relating to flexibly-sized objects in nios2 backend.

2019-12-01  Sandra Loosemore  <sandra@codesourcery.com>

	Fix bugs relating to flexibly-sized objects in nios2 backend.

	PR target/92499

	gcc/c/
	* c-decl.c (flexible_array_type_p): Move to common code.

	gcc/
	* config/nios2/nios2.c (nios2_in_small_data_p): Do not consider
	objects of flexible types to be small if they have internal linkage
	or are declared extern.
	* config/nios2/nios2.h (ASM_OUTPUT_ALIGNED_LOCAL): Replace with...
	(ASM_OUTPUT_ALIGNED_DECL_LOCAL): ...this.  Use targetm.in_small_data_p
	instead of the size of the object initializer.
	* tree.c (flexible_array_type_p): Move from C front end, and
	generalize to handle fields in non-C structures.
	* tree.h (flexible_array_type_p): Declare.

	gcc/testsuite/
	* gcc.target/nios2/pr92499-1.c: New.
	* gcc.target/nios2/pr92499-2.c: New.
	* gcc.target/nios2/pr92499-3.c: New.

From-SVN: r278891

1 files changed, 16 insertions, 0 deletions

diff --git a/gcc/config/nios2/nios2.c b/gcc/config/nios2/nios2.c
index 4cea0f4e2f2..ca6222658a9 100644
--- a/gcc/config/nios2/nios2.c
+++ b/gcc/config/nios2/nios2.c
@@ -2373,6 +2373,22 @@ nios2_in_small_data_p (const_tree exp)
 	  if (nios2_small_section_name_p (section))
 	    return true;
 	}
+      else if (flexible_array_type_p (TREE_TYPE (exp))
+	       && (!TREE_PUBLIC (exp) || DECL_EXTERNAL (exp)))
+	{
+	  /* We really should not consider any objects of any flexibly-sized
+	     type to be small data, but pre-GCC 10 did not test
+	     for this and just fell through to the next case.  Thus older
+	     code compiled with -mgpopt=global could contain GP-relative
+	     accesses to objects defined in this compilation unit with
+	     external linkage.  We retain the possible small-data treatment
+	     of such definitions for backward ABI compatibility, but
+	     no longer generate GP-relative accesses for external
+	     references (so that the ABI could be changed in the future
+	     with less potential impact), or objects with internal
+	     linkage.  */
+	  return false;
+	}
       else
 	{
 	  HOST_WIDE_INT size = int_size_in_bytes (TREE_TYPE (exp));