i386.opt (-mstackrealign): New flag.

        * gcc/config/i386/i386.opt (-mstackrealign): New flag.  *
	gcc/config/i386/i386.c (force_align_arg_pointer): New attribute.
	(ix86_handle_cconv_attribute): Emit error when
	force_align_arg_pointer attribute collides with too many regparms.
	(ix86_function_regparm): Limit regparms when used with
	force_align_arg_pointer attribute.  (ix86_internal_arg_pointer):
	Support stack-realigning prologue in non-main functions.  Emit
	warning for nested functions under -mstackrealign, emit error for
	nested functions with force_align_arg_pointer attribute.
	* gcc/doc/extend.texi (force_align_arg_pointer): Document it.
	* gcc/doc/invoke.texi (-mstackrealign): Document it.
	* testsuite/gcc.target/i386/20060512-1.c: New.
	* testsuite/gcc.target/i386/20060512-2.c: New.
	* testsuite/gcc.target/i386/20060512-3.c: New.
	* testsuite/gcc.target/i386/20060512-4.c: New.

From-SVN: r113880

2 files changed, 30 insertions, 0 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index a72fb7f..a281f92 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -2207,6 +2207,20 @@ SSE registers instead of on the stack.  Functions that take a
 variable number of arguments will continue to pass all of their
 floating point arguments on the stack.
 
+@item force_align_arg_pointer
+@cindex @code{force_align_arg_pointer} attribute
+On the Intel x86, the @code{force_align_arg_pointer} attribute may be
+applied to individual function definitions, generating an alternate
+prologue and epilogue that realigns the runtime stack.  This supports
+mixing legacy codes that run with a 4-byte aligned stack with modern
+codes that keep a 16-byte stack for SSE compatibility.  The alternate
+prologue and epilogue are slower and bigger than the regular ones, and
+the alternate prologue requires a scratch register; this lowers the
+number of registers available if used in conjunction with the
+@code{regparm} attribute.  The @code{force_align_arg_pointer}
+attribute is incompatible with nested functions; this is considered a
+hard error.
+
 @item returns_twice
 @cindex @code{returns_twice} attribute
 The @code{returns_twice} attribute tells the compiler that a function may
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index df6074c..9ac49e9 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -537,6 +537,7 @@ Objective-C and Objective-C++ Dialects}.
 -mthreads  -mno-align-stringops  -minline-all-stringops @gol
 -mpush-args  -maccumulate-outgoing-args  -m128bit-long-double @gol
 -m96bit-long-double  -mregparm=@var{num}  -msseregparm @gol
+-mstackrealign @gol
 -momit-leaf-frame-pointer  -mno-red-zone -mno-tls-direct-seg-refs @gol
 -mcmodel=@var{code-model} @gol
 -m32  -m64 -mlarge-data-threshold=@var{num}}
@@ -9464,6 +9465,21 @@ function by using the function attribute @samp{sseregparm}.
 modules with the same value, including any libraries.  This includes
 the system libraries and startup modules.
 
+@item -mstackrealign
+@opindex mstackrealign
+Realign the stack at entry.  On the Intel x86, the
+@option{-mstackrealign} option will generate an alternate prologue and
+epilogue that realigns the runtime stack.  This supports mixing legacy
+codes that keep a 4-byte aligned stack with modern codes that keep a
+16-byte stack for SSE compatibility.  The alternate prologue and
+epilogue are slower and bigger than the regular ones, and the
+alternate prologue requires an extra scratch register; this lowers the
+number of registers available if used in conjunction with the
+@code{regparm} attribute.  The @option{-mstackrealign} option is
+incompatible with the nested function prologue; this is considered a
+hard error.  See also the attribute @code{force_align_arg_pointer},
+applicable to individual functions.
+
 @item -mpreferred-stack-boundary=@var{num}
 @opindex mpreferred-stack-boundary
 Attempt to keep the stack boundary aligned to a 2 raised to @var{num}