[PATCH]: eliminate uses of real_sqrt in builtins.c

["Kaveh R. GHAZI" <ghazi at caip dot rutgers dot edu>]

I realized with my last patch, I'm introducing more uses of real_sqrt and
I'm thinking we want to go in the other direction.  Since all we really
want in these cases is the square root of two, I added that to our list of
constants.  I took the opportunity to delete dconstpi which is no longer
used on mainline, and present that as a peace offering to those who
dislike adding more startup cruft. :-)

I copied the first N digits of sqrt(2) from here:
http://www.ibiblio.org/pub/docs/books/gutenberg/etext94/2sqrt10a.txt

Note the folding transformation uses dconstsqrt2, while the testcases
(which all pass) compare the result with __builtin_sqrt(2) which uses MPFR
to resolve.  So they are consistent at least up to the precision of long
double (128 bits on my box).

Bootstrapped on sparc-sun-solaris2.10 in conjunction with my previous
patch to cabs, which is necessary for a clean apply:
http://gcc.gnu.org/ml/gcc-patches/2007-02/msg00272.html

There were no regressions.  With these removed, there's only one use of
real_sqrt left in simplify-rtx.c.

Okay for mainline?

		Thanks,
		--Kaveh


2007-02-02  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>

	* emit-rtl.c (dconstpi): Delete.
	(dconstsqrt2): New.
	(init_emit_once): Delete dconstpi and init dconstsqrt2.
	* real.h (dconstpi): Delete.
	(dconstsqrt2): New.
	* builtins.c (fold_builtin_cabs): Use dconstsqrt2.
	(fold_builtin_hypot): Likewise.

diff -rup orig/egcc-SVN20070202/gcc/emit-rtl.c egcc-SVN20070202/gcc/emit-rtl.c
--- orig/egcc-SVN20070202/gcc/emit-rtl.c	2007-02-01 20:02:48.000000000 -0500
+++ egcc-SVN20070202/gcc/emit-rtl.c	2007-02-02 20:21:50.285384653 -0500
@@ -105,7 +105,7 @@ REAL_VALUE_TYPE dconstm1;
 REAL_VALUE_TYPE dconstm2;
 REAL_VALUE_TYPE dconsthalf;
 REAL_VALUE_TYPE dconstthird;
-REAL_VALUE_TYPE dconstpi;
+REAL_VALUE_TYPE dconstsqrt2;
 REAL_VALUE_TYPE dconste;

 /* All references to the following fixed hard registers go through
@@ -5181,8 +5181,8 @@ init_emit_once (int line_numbers)

   /* Initialize mathematical constants for constant folding builtins.
      These constants need to be given to at least 160 bits precision.  */
-  real_from_string (&dconstpi,
-    "3.1415926535897932384626433832795028841971693993751058209749445923078");
+  real_from_string (&dconstsqrt2,
+    "1.4142135623730950488016887242096980785696718753769480731766797379907");
   real_from_string (&dconste,
     "2.7182818284590452353602874713526624977572470936999595749669676277241");

diff -rup orig/egcc-SVN20070202/gcc/real.h egcc-SVN20070202/gcc/real.h
--- orig/egcc-SVN20070202/gcc/real.h	2007-01-18 20:02:49.000000000 -0500
+++ egcc-SVN20070202/gcc/real.h	2007-02-02 20:21:50.288190410 -0500
@@ -387,7 +387,7 @@ extern REAL_VALUE_TYPE dconstm1;
 extern REAL_VALUE_TYPE dconstm2;
 extern REAL_VALUE_TYPE dconsthalf;
 extern REAL_VALUE_TYPE dconstthird;
-extern REAL_VALUE_TYPE dconstpi;
+extern REAL_VALUE_TYPE dconstsqrt2;
 extern REAL_VALUE_TYPE dconste;

 /* Function to return a real value (not a tree node)
diff -rup orig/egcc-SVN20070202/gcc/builtins.c egcc-SVN20070202/gcc/builtins.c
--- orig/egcc-SVN20070202/gcc/builtins.c	2007-02-02 20:24:00.207385898 -0500
+++ egcc-SVN20070202/gcc/builtins.c	2007-02-02 20:25:04.303651679 -0500
@@ -7158,13 +7158,12 @@ fold_builtin_cabs (tree arglist, tree ty
       if (flag_unsafe_math_optimizations
 	  && operand_equal_p (real, imag, OEP_PURE_SAME))
         {
-	  REAL_VALUE_TYPE sqrt2;
-
-	  real_sqrt (&sqrt2, TYPE_MODE (type), &dconst2);
+	  const REAL_VALUE_TYPE sqrt2_trunc
+	    = real_value_truncate (TYPE_MODE (type), dconstsqrt2);
 	  STRIP_NOPS (real);
 	  return fold_build2 (MULT_EXPR, type,
 			      fold_build1 (ABS_EXPR, type, real),
-			      build_real (type, sqrt2));
+			      build_real (type, sqrt2_trunc));
 	}
     }

@@ -8059,12 +8058,11 @@ fold_builtin_hypot (tree fndecl, tree ar
   if (flag_unsafe_math_optimizations
       && operand_equal_p (arg0, arg1, OEP_PURE_SAME))
     {
-      REAL_VALUE_TYPE sqrt2;
-
-      real_sqrt (&sqrt2, TYPE_MODE (type), &dconst2);
+      const REAL_VALUE_TYPE sqrt2_trunc
+	= real_value_truncate (TYPE_MODE (type), dconstsqrt2);
       return fold_build2 (MULT_EXPR, type,
 			  fold_build1 (ABS_EXPR, type, arg0),
-			  build_real (type, sqrt2));
+			  build_real (type, sqrt2_trunc));
     }

   return NULL_TREE;