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.

7 files changed, 68 insertions, 12 deletions

diff --git a/gcc/config.gcc b/gcc/config.gcc
index bf1c745..294f312 100644
--- a/gcc/config.gcc
+++ b/gcc/config.gcc
@@ -677,6 +677,20 @@ case ${target} in
     macos_min=0
   fi
   def_ld64=85.2
+  # Tools hosted on earlier versions of Darwin constrained all object
+  # alignment to be 2^15 or smaller.  From Darwin11 (macOS 10.7) the
+  # alignment of non-common is allowed to be up to 2^28.  Note that the
+  # larger alignment is permitted when targeting 10.6 from 10.7 so that
+  # the constraint only need be applied per host (and only if the host
+  # is Darwin).
+  case ${host} in
+      *-*-darwin[4-9]* | *-*-darwin10*)
+          tm_defines="$tm_defines L2_MAX_OFILE_ALIGNMENT=15U"
+          ;;
+      *)
+          tm_defines="$tm_defines L2_MAX_OFILE_ALIGNMENT=28U"
+          ;;
+  esac
   case ${target} in
       # Darwin 4 to 19 correspond to macOS 10.0 to 10.15
       *-*-darwin[4-9]* | *-*-darwin1[0-9]*)
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)		\
diff --git a/gcc/testsuite/gcc.dg/attr-aligned.c b/gcc/testsuite/gcc.dg/attr-aligned.c
index ec54563..a2e11c9 100644
--- a/gcc/testsuite/gcc.dg/attr-aligned.c
+++ b/gcc/testsuite/gcc.dg/attr-aligned.c
@@ -12,8 +12,12 @@
 #  define ALIGN_MAX_STATIC      0x1000
    /* Excessive alignment for functions and objects with static storage
       duration that's expected to trigger an error.  */
-#elif __MACH__
-#  define ALIGN_MAX_STATIC      0x8000
+#elif __APPLE__
+# if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 1070
+#   define ALIGN_MAX_STATIC      0x8000
+# else
+#   define ALIGN_MAX_STATIC      ALIGN_MAX_HARD
+# endif
 #elif pdp11
 #  define ALIGN_MAX_STATIC      2
 /* Work around a pdp11 ICE (see PR target/87821).  */
diff --git a/gcc/testsuite/gcc.dg/darwin-aligned-globals.c b/gcc/testsuite/gcc.dg/darwin-aligned-globals.c
new file mode 100644
index 0000000..18b71e7
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/darwin-aligned-globals.c
@@ -0,0 +1,24 @@
+/* { dg-do compile { target *-*-darwin* } } */
+/* { dg-additional-options "-fcommon" } */
+
+/* Test alignment rules which differ for earlier hosts (so we must
+   work on the principle that this test will be exercised by self-
+   hosted compilers. */
+
+#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 1070
+#define align_OK (1ul << 28)
+#define align_BAD (1ul << 29)
+#else
+#define align_OK (1ul << 15)
+#define align_BAD (1ul << 16)
+#endif
+
+/* All non common vars are allowed larger alignment on modern systems.  */
+static int xn __attribute__ ((aligned (align_OK)));
+static int xi __attribute__ ((aligned (align_OK))) = 5  ;
+int gxi __attribute__ ((aligned (align_OK))) = 6 ;
+
+/* test that we detect bad cases.  */
+static int yn __attribute__ ((aligned (align_BAD))); /* { dg-error {requested alignment .[0-9]+. exceeds object file maximum} } */
+static int yi __attribute__ ((aligned (align_BAD))) = 5;  /* { dg-error {requested alignment .[0-9]+. exceeds object file maximum} } */
+int yni __attribute__ ((aligned (align_BAD))) = 6;  /* { dg-error {requested alignment .[0-9]+. exceeds object file maximum} } */
diff --git a/gcc/testsuite/gcc.dg/darwin-comm-1.c b/gcc/testsuite/gcc.dg/darwin-comm-1.c
new file mode 100644
index 0000000..4651998
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/darwin-comm-1.c
@@ -0,0 +1,5 @@
+/* { dg-do compile { target *-*-darwin[912]* } } */
+/* { dg-options "-fcommon" } */
+
+/* In all cases, common has a max alignment of 2^15.  */
+int badcommon __attribute__ ((aligned (65536))); /* { dg-error "common variables must have an alignment" } */
diff --git a/gcc/testsuite/gcc.target/i386/pr89261.c b/gcc/testsuite/gcc.target/i386/pr89261.c
index c5c4273..b599d49 100644
--- a/gcc/testsuite/gcc.target/i386/pr89261.c
+++ b/gcc/testsuite/gcc.target/i386/pr89261.c
@@ -5,6 +5,7 @@
 typedef double __v2df __attribute__ ((vector_size (16), aligned (1 << 28)));
 
 __v2df foo = { 1.0, 2.0 };
-/* { dg-error {alignment of 'foo' is greater than maximum object file alignment 32768} "" { target *-*-darwin* } .-1 } */
+/* { dg-error {alignment of 'foo' is greater than maximum object file alignment 32768} "" { target { *-*-darwin[89]*  *-*-darwin10* } } .-1 } */
 
 /* { dg-final { scan-assembler "\.align\[ \t]+268435456" { target { ! *-*-darwin* } } } } */
+/* { dg-final { scan-assembler "\.align\[ \t]+28" { target { *-*-darwin1[1-9]* *-*-darwin2* } } } } */