re PR c/24644 (gcc-4.1 compiled ppc64 kernels do not boot)

        PR 24644
        * common.opt (Wvolatile-register-var): New.
        * varasm.c (make_decl_rtl): Only emit warning when option
        specified.  Clarify warning message.
        * doc/invoke.texi (Wvolatile-register-var): Document new option.

        * doc/md.texi (copysign): Document standard named pattern.

From-SVN: r106791

gcc/ChangeLog

+2005-11-11  David Edelsohn  <edelsohn@gnu.org>
+
+	PR 24644
+	* common.opt (Wvolatile-register-var): New.
+	* varasm.c (make_decl_rtl): Only emit warning when option
+	specified.  Clarify warning message.
+	* doc/invoke.texi (Wvolatile-register-var): Document new option.
+
+	* doc/md.texi (copysign): Document standard named pattern.
+
 2005-11-11  Jie Zhang  <jie.zhang@analog.com>
 
 	* config/bfin/bfin.c (bfin_expand_strmov): Correctly move the trailing

gcc/common.opt

@@ -173,6 +173,10 @@ Wunused-variable
 Common Var(warn_unused_variable)
 Warn when a variable is unused
 
+Wvolatile-register-var
+Common Var(warn_register_var)
+Warn when a register variable is declared volatile
+
 aux-info
 Common Separate
 -aux-info <file>	Emit declaration information into <file>

gcc/doc/invoke.texi

@@ -245,7 +245,7 @@ Objective-C and Objective-C++ Dialects}.
 -Wunknown-pragmas  -Wno-pragmas -Wunreachable-code @gol
 -Wunused  -Wunused-function  -Wunused-label  -Wunused-parameter @gol
 -Wunused-value  -Wunused-variable  -Wvariadic-macros @gol
--Wwrite-strings}
+-Wvolatile-register-var  -Wwrite-strings}
 
 @item C-only Warning Options
 @gccoptlist{-Wbad-function-cast  -Wmissing-declarations @gol
@@ -3370,6 +3370,13 @@ Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU
 alternate syntax when in pedantic ISO C99 mode.  This is default.
 To inhibit the warning messages, use @option{-Wno-variadic-macros}.
 
+@item -Wvolatile-register-var
+@opindex Wvolatile-register-var
+@opindex Wno-volatile-register-var
+Warn if a register variable is declared volatile.  The volatile
+modifier does not inhibit all optimizations that may eliminate reads
+and/or writes to register variables.
+
 @item -Wdisabled-optimization
 @opindex Wdisabled-optimization
 Warn if a requested optimization pass is disabled.  This warning does

gcc/doc/md.texi

@@ -3306,6 +3306,16 @@ corresponds to the C data type @code{double} and the @code{rintf}
 built-in function uses the mode which corresponds to the C data
 type @code{float}.
 
+@cindex @code{copysign@var{m}3} instruction pattern
+@item @samp{copysign@var{m}3}
+Store a value with the magnitude of operand 1 and the sign of operand
+2 into operand 0.
+
+The @code{copysign} built-in function of C always uses the mode which
+corresponds to the C data type @code{double} and the @code{copysignf}
+built-in function uses the mode which corresponds to the C data
+type @code{float}.
+
 @cindex @code{ffs@var{m}2} instruction pattern
 @item @samp{ffs@var{m}2}
 Store into operand 0 one plus the index of the least significant 1-bit

gcc/varasm.c

@@ -955,8 +955,9 @@ make_decl_rtl (tree decl)
 	      error ("global register variable has initial value");
 	    }
 	  if (TREE_THIS_VOLATILE (decl))
-	    warning (0, "volatile register variables don%'t "
-		     "work as you might wish");
+	    warning (OPT_Wvolatile_register_var,
+		     "optimization may eliminate reads and/or "
+		     "writes to register variables");
 
 	  /* If the user specified one of the eliminables registers here,
 	     e.g., FRAME_POINTER_REGNUM, we don't want to get this variable