Darwin: Update rules for handling alignment of globals.

The current rule was too strict and has not been required since Darwin11.

This relaxes the constraint to allow up to 2^28 alignment for non-common
entities.  Common is still restricted to a maximum aligment of 2^15.

When the host is an older version of Darwin ( earlier that 11 ) then the
existing constraint is still applied.  Note that this is a host constraint
not a target one (so that a compilation on 10.7 targeting 10.6 is allowed
to use a greater alignment than the tools on 10.6 support).  This matches
the behaviour of clang.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

gcc/ChangeLog:

	* config.gcc: Emit L2_MAX_OFILE_ALIGNMENT with suitable
	values for the host.
	* config/darwin.c (darwin_emit_common): Error for alignment
	values > 32768.
	* config/darwin.h (MAX_OFILE_ALIGNMENT): Rework to use the
	configured L2_MAX_OFILE_ALIGNMENT.

gcc/testsuite/ChangeLog:

	* gcc.dg/darwin-aligned-globals.c: New test.
	* gcc.dg/darwin-comm-1.c: New test.
	* gcc.dg/attr-aligned.c: Amend for new alignment values on
	Darwin.
	* gcc.target/i386/pr89261.c: Likewise.

2 files changed, 17 insertions, 9 deletions

diff --git a/gcc/config/darwin.c b/gcc/config/darwin.c
index e580319..5045b68 100644
--- a/gcc/config/darwin.c
+++ b/gcc/config/darwin.c
@@ -2558,7 +2558,6 @@ darwin_emit_common (FILE *fp, const char *name,
     rounded = (size + (align-1)) & ~(align-1);
 
   l2align = floor_log2 (align);
-  gcc_assert (l2align <= L2_MAX_OFILE_ALIGNMENT);
 
   in_section = comm_section;
   /* We mustn't allow multiple public symbols to share an address when using
@@ -2709,6 +2708,10 @@ darwin_asm_output_aligned_decl_common (FILE *fp, tree decl, const char *name,
 #ifdef DEBUG_DARWIN_MEM_ALLOCATORS
 fprintf (fp, "# adcom: %s (%d,%d) decl=0x0\n", name, (int)size, (int)align);
 #endif
+     /* Common variables are limited to a maximum alignment of 2^15.  */
+      if (align > 32768)
+	error_at (UNKNOWN_LOCATION, "common variables must have an alignment"
+		  " of 32678 or less");
       darwin_emit_common (fp, name, size, align);
       return;
     }
@@ -2736,7 +2739,7 @@ fprintf (fp, "# adcom: %s (%lld,%d) ro %d cst %d stat %d com %d pub %d"
     }
 
   /* We shouldn't be messing with this if the decl has a section name.  */
-  gcc_assert (DECL_SECTION_NAME (decl) == NULL);
+  gcc_checking_assert (DECL_SECTION_NAME (decl) == NULL);
 
   /* We would rather not have to check this here - but it seems that we might
      be passed a decl that should be in coalesced space.  */
@@ -2765,10 +2768,16 @@ fprintf (fp, "# adcom: %s (%lld,%d) ro %d cst %d stat %d com %d pub %d"
 
   l2align = floor_log2 (align / BITS_PER_UNIT);
   /* Check we aren't asking for more aligment than the platform allows.  */
-  gcc_assert (l2align <= L2_MAX_OFILE_ALIGNMENT);
+  gcc_checking_assert (l2align <= L2_MAX_OFILE_ALIGNMENT);
 
   if (TREE_PUBLIC (decl) != 0)
-    darwin_emit_common (fp, name, size, align);
+    {
+      /* Common variables are limited to a maximum alignment of 2^15.  */
+      if (l2align > 15)
+	error_at (DECL_SOURCE_LOCATION (decl), "common variables must have"
+		  " an alignment of 32678 or less");
+      darwin_emit_common (fp, name, size, align);
+    }
   else
     darwin_emit_local_bss (fp, decl, name, size, l2align);
 }
diff --git a/gcc/config/darwin.h b/gcc/config/darwin.h
index c175ead..d6f52e7 100644
--- a/gcc/config/darwin.h
+++ b/gcc/config/darwin.h
@@ -873,13 +873,12 @@ int darwin_label_is_anonymous_local_objc_name (const char *name);
   if ((LOG) != 0)			\
     fprintf (FILE, "\t%s\t%d\n", ALIGN_ASM_OP, (LOG))
 
-/* The maximum alignment which the object file format can support in
-   bits.  For Mach-O, this is 2^15 bytes.  */
+/* The maximum alignment which the object file format can support in bits
+   which depends on the OS version and whether the object is a common
+   variable.  */
 
 #undef	MAX_OFILE_ALIGNMENT
-#define MAX_OFILE_ALIGNMENT (0x8000 * 8)
-
-#define L2_MAX_OFILE_ALIGNMENT 15
+#define MAX_OFILE_ALIGNMENT ((1U << L2_MAX_OFILE_ALIGNMENT) * 8U)
 
 /*  These are the three variants that emit referenced blank space.  */
 #define ASM_OUTPUT_ALIGNED_BSS(FILE, DECL, NAME, SIZE, ALIGN)		\