[patch] m68k: Fix binary compatibility problem with -mno-strict-align. (Take 2)

[Kazu Hirata <kazu at codesourcery dot com>]

Hi,

Attached is a revised patch to fix binary compatibility problem with
-mno-strict-align on m68k-elf.

The previous iteration of this patch is at:

  http://gcc.gnu.org/ml/gcc-patches/2007-07/msg01437.html

In this iteration, Nathan has made a change to effectively comment out
TARGET_RETURN_IN_MEMORY and m68k_return_in_memory if
M68K_HONOR_TARGET_STRICT_ALIGNMENT is defined.  This way, this patch
has no effect on m68k-linux, preserving the ABI.

Tested on m68k-elf.  OK to apply?

Kazu Hirata

2007-08-25  Nathan Sidwell  <nathan@codesourcery.com>
	    Kazu Hirata  <kazu@codesourcery.com>

	* gcc/config/m68k/linux.h
	(M68K_HONOR_TARGET_STRICT_ALIGNMENT): Redefine as 0.
	* config/m68k/m68k.c (TARGET_RETURN_IN_MEMORY): New.
	(m68k_return_in_memory): New.
	* gcc/config/m68k/m68k.h (M68K_HONOR_TARGET_STRICT_ALIGNMENT):
	New.

Index: gcc/config/m68k/linux.h
===================================================================
--- gcc/config/m68k/linux.h	(revision 127787)
+++ gcc/config/m68k/linux.h	(working copy)
@@ -31,6 +31,8 @@ along with GCC; see the file COPYING3.  
 
 #undef STRICT_ALIGNMENT
 #define STRICT_ALIGNMENT 0
+#undef M68K_HONOR_TARGET_STRICT_ALIGNMENT
+#define M68K_HONOR_TARGET_STRICT_ALIGNMENT 0
 
 /* Here are four prefixes that are used by asm_fprintf to
    facilitate customization for alternate assembler syntaxes.
Index: gcc/config/m68k/m68k.c
===================================================================
--- gcc/config/m68k/m68k.c	(revision 127787)
+++ gcc/config/m68k/m68k.c	(working copy)
@@ -134,6 +134,9 @@ static void m68k_compute_frame_layout (v
 static bool m68k_save_reg (unsigned int regno, bool interrupt_handler);
 static bool m68k_ok_for_sibcall_p (tree, tree);
 static bool m68k_rtx_costs (rtx, int, int, int *);
+#if M68K_HONOR_TARGET_STRICT_ALIGNMENT
+static bool m68k_return_in_memory (tree, tree);
+#endif
 
 
 /* Specify the identification number of the library being built */
@@ -205,6 +208,11 @@ int m68k_last_compare_had_fp_operands;
 #undef TARGET_FUNCTION_OK_FOR_SIBCALL
 #define TARGET_FUNCTION_OK_FOR_SIBCALL m68k_ok_for_sibcall_p
 
+#if M68K_HONOR_TARGET_STRICT_ALIGNMENT
+#undef TARGET_RETURN_IN_MEMORY
+#define TARGET_RETURN_IN_MEMORY m68k_return_in_memory
+#endif
+
 static const struct attribute_spec m68k_attribute_table[] =
 {
   /* { name, min_len, max_len, decl_req, type_req, fn_type_req, handler } */
@@ -4386,3 +4394,25 @@ m68k_function_value (const_tree valtype,
   else
     return gen_rtx_REG (mode, D0_REG);
 }
+
+/* Worker function for TARGET_RETURN_IN_MEMORY.  */
+#if M68K_HONOR_TARGET_STRICT_ALIGNMENT
+static bool
+m68k_return_in_memory (tree type, tree fntype ATTRIBUTE_UNUSED)
+{
+  enum machine_mode mode = TYPE_MODE (type);
+
+  if (mode == BLKmode)
+    return true;
+
+  /* If TYPE's known alignment is less than the alignment of MODE that
+     would contain the structure, then return in memory.  We need to
+     do so to maintain the compatibility between code compiled with
+     -mstrict-align and that compiled with -mno-strict-align.  */
+  if (AGGREGATE_TYPE_P (type)
+      && TYPE_ALIGN (type) < GET_MODE_ALIGNMENT (mode))
+    return true;
+
+  return false;
+}
+#endif
Index: gcc/config/m68k/m68k.h
===================================================================
--- gcc/config/m68k/m68k.h	(revision 127787)
+++ gcc/config/m68k/m68k.h	(working copy)
@@ -310,6 +310,7 @@ along with GCC; see the file COPYING3.  
 #define BIGGEST_ALIGNMENT (TARGET_ALIGN_INT ? 32 : 16)
 
 #define STRICT_ALIGNMENT (TARGET_STRICT_ALIGNMENT)
+#define M68K_HONOR_TARGET_STRICT_ALIGNMENT 1
 
 #define INT_TYPE_SIZE (TARGET_SHORT ? 16 : 32)