PATCH: PR target/53383: Allow -mpreferred-stack-boundary=3 on x86-64

[H.J. Lu]

Hi,

This patch allows -mpreferred-stack-boundary=3 on x86-64 when SSE is
disabled.  Since this option changes ABI, I also added a warning for
-mpreferred-stack-boundary=3.  OK for trunk?

Thanks.


H.J.
----
        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 disenabled.

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

diff --git a/gcc/config/i386/i386.c b/gcc/config/i386/i386.c
index eca542c..338d387 100644
--- a/gcc/config/i386/i386.c
+++ b/gcc/config/i386/i386.c
@@ -3660,7 +3660,7 @@ 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
diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
index ddb3645..f7f13d2 100644
--- a/gcc/config/i386/i386.h
+++ b/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.  */
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 4c5c79f..daa1f3a 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -13521,6 +13521,12 @@ 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