Allow -mpreferred-stack-boundary=3 on x86-64

	PR target/53383
	* doc/invoke.texi: Add a warning for -mpreferred-stack-boundary=3.

	* config/i386/i386.c (ix86_option_override_internal): Allow
	-mpreferred-stack-boundary=3 for 64-bit if SSE is disabled.

	* config/i386/i386.h (MIN_STACK_BOUNDARY): Set to 64 for 64-bit
	if SSE is disabled.

From-SVN: r188893

gcc/ChangeLog

+2012-06-22  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR target/53383
+	* doc/invoke.texi: Add a warning for -mpreferred-stack-boundary=3.
+
+	* config/i386/i386.c (ix86_option_override_internal): Allow
+	-mpreferred-stack-boundary=3 for 64-bit if SSE is disabled.
+
+	* config/i386/i386.h (MIN_STACK_BOUNDARY): Set to 64 for 64-bit
+	if SSE is disabled.
+
 2012-06-22  Bill Schmidt  <wschmidt@linux.ibm.com>
 
 	* double-int.c (double_int_multiple_of): New function.

gcc/config/i386/i386.c

@@ -3664,7 +3664,7 @@ ix86_option_override_internal (bool main_args_p)
   ix86_preferred_stack_boundary = PREFERRED_STACK_BOUNDARY_DEFAULT;
   if (global_options_set.x_ix86_preferred_stack_boundary_arg)
     {
-      int min = (TARGET_64BIT ? 4 : 2);
+      int min = (TARGET_64BIT ? (TARGET_SSE ? 4 : 3) : 2);
       int max = (TARGET_SEH ? 4 : 12);
 
       if (ix86_preferred_stack_boundary_arg < min

gcc/config/i386/i386.h

@@ -708,7 +708,7 @@ enum target_cpu_default
 #define MAIN_STACK_BOUNDARY (TARGET_64BIT ? 128 : 32)
 
 /* Minimum stack boundary.  */
-#define MIN_STACK_BOUNDARY (TARGET_64BIT ? 128 : 32)
+#define MIN_STACK_BOUNDARY (TARGET_64BIT ? (TARGET_SSE ? 128 : 64) : 32)
 
 /* Boundary (in *bits*) on which the stack pointer prefers to be
    aligned; the compiler cannot rely on having this alignment.  */

gcc/doc/invoke.texi

@@ -13577,6 +13577,12 @@ Attempt to keep the stack boundary aligned to a 2 raised to @var{num}
 byte boundary.  If @option{-mpreferred-stack-boundary} is not specified,
 the default is 4 (16 bytes or 128 bits).
 
+@strong{Warning:} When generating code for the x86-64 architecture with
+SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be
+used to keep the stack boundary aligned to 8 byte boundary.  You must
+build all modules with @option{-mpreferred-stack-boundary=3}, including
+any libraries.  This includes the system libraries and startup modules.
+
 @item -mincoming-stack-boundary=@var{num}
 @opindex mincoming-stack-boundary
 Assume the incoming stack is aligned to a 2 raised to @var{num} byte