re PR middle-end/43419 (gcc replaces pow(x, 0.5) by sqrt(x), invalid when x is -0)

	PR middle-end/43419
	* builtins.c (expand_builtin_pow): Don't transform pow(x, 0.5)
	into sqrt(x) if we need to preserve signed zeros.

testsuite/
	* gcc.dg/pr43419.c: New testcase.

From-SVN: r157543

gcc/ChangeLog

+2010-03-18  Michael Matz  <matz@suse.de>
+
+	PR middle-end/43419
+	* builtins.c (expand_builtin_pow): Don't transform pow(x, 0.5)
+	into sqrt(x) if we need to preserve signed zeros.
+
 2010-03-18  Steven Bosscher  <steven@gcc.gnu.org>
 	    Eric Botcazou  <ebotcazou@adacore.com>
 

gcc/builtins.c

@@ -2980,7 +2980,10 @@ expand_builtin_pow (tree exp, rtx target, rtx subtarget)
 	  && ((flag_unsafe_math_optimizations
 	       && optimize_insn_for_speed_p ()
 	       && powi_cost (n/2) <= POWI_MAX_MULTS)
-	      || n == 1))
+	      /* Even the c==0.5 case cannot be done unconditionally
+	         when we need to preserve signed zeros, as
+		 pow (-0, 0.5) is +0, while sqrt(-0) is -0.  */
+	      || (!HONOR_SIGNED_ZEROS (mode) && n == 1)))
 	{
 	  tree call_expr = build_call_nofold (fn, 1, narg0);
 	  /* Use expand_expr in case the newly built call expression

gcc/testsuite/ChangeLog

+2010-03-18  Michael Matz  <matz@suse.de>
+
+	PR middle-end/43419
+	* gcc.dg/pr43419.c: New testcase.
+
 2010-03-18  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR rtl-optimization/43360
@@ -16,10 +21,10 @@
 2010-03-17  Jerry DeLisle  <jvdelisle@gcc.gnu.org>
 
 	PR libfortran/43265
-	*gfortran.dg/read_empty_file.f: New test.
-	*gfortran.dg/read_eof_all.f90: New test.
-	*gfortran.dg/namelist_27.f90: Eliminate infinite loop posibility.
-	*gfortran.dg/namelist_28.f90: Eliminate infinite loop posibility.
+	* gfortran.dg/read_empty_file.f: New test.
+	* gfortran.dg/read_eof_all.f90: New test.
+	* gfortran.dg/namelist_27.f90: Eliminate infinite loop posibility.
+	* gfortran.dg/namelist_28.f90: Eliminate infinite loop posibility.
 
 2010-03-17  Michael Matz  <matz@suse.de>
 

gcc/testsuite/gcc.dg/pr43419.c

+/* { dg-do run } */
+/* { dg-options "-O1" } */
+/* { dg-add-options ieee } */
+#include <math.h>
+
+extern void abort (void);
+void __attribute__((noinline)) f (double x)
+{
+  double pluszero = pow (x, 0.5);
+  double minuszero = sqrt (x);
+  if (signbit (pluszero) == signbit (minuszero))
+    abort ();
+}
+
+int main(void)
+{
+  f (-0.0);
+  return 0;
+}