[Bug middle-end/40106] [4.4/4.5 Regression] Weird interaction between optimize_insn_for_speed_p and -funsafe-math-optimizations

[rguenth at gcc dot gnu dot org]

------- Comment #48 from rguenth at gcc dot gnu dot org  2010-03-19 10:35 -------
Untested patch doing 2):

Index: builtins.c
===================================================================
--- builtins.c  (revision 157561)
+++ builtins.c  (working copy)
@@ -2980,10 +2980,16 @@ expand_builtin_pow (tree exp, rtx target
          && ((flag_unsafe_math_optimizations
               && optimize_insn_for_speed_p ()
               && powi_cost (n/2) <= POWI_MAX_MULTS)
-             /* Even the c==0.5 case cannot be done unconditionally
+             /* 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)))
+             || (!HONOR_SIGNED_ZEROS (mode) && n == 1)
+             /* For c == 1.5 we can assume that x * sqrt (x) is always
+                smaller than pow (x, 1.5) if sqrt will not be expanded
+                as a call.  */
+             || (n == 2
+                 && (optab_handler (sqrt_optab, mode)->insn_code
+                     != CODE_FOR_nothing))))
        {
          tree call_expr = build_call_nofold (fn, 1, narg0);
          /* Use expand_expr in case the newly built call expression


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40106