[Bug target/108922] fmod() 13x slowdown in gcc4.9 dropping "fprem" and calling fmod()

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108922

--- Comment #30 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Jakub Jelinek from comment #29)
> Note, fmod_optab is only used on i?86 (where because of the commit mentioned
> here it was limited to finite math only) and rs6000 (which guards it on
> unsafe math optimizations), so both in the fast-math related area only.
> Therefore it might be very well possible it got broken because of those
> changes without anyone noticing.  Most of the builtins for which ranges are
> tested are single operand and pow which has 2 has special handling...

Looking at r6-4983-g883cabdecdb052865f, fmod handled here:

+/* Return true if CALL can produce a domain error (EDOM) but can never
+   produce a pole, range overflow or range underflow error (all ERANGE).
+   This means that we can tell whether a function would have set errno
+   by testing whether the result is a NaN.  */
+
+static bool
+edom_only_function (gcall *call)
+{
+  switch (DECL_FUNCTION_CODE (gimple_call_fndecl (call)))
+    {
+    CASE_FLT_FN (BUILT_IN_ACOS):
+    CASE_FLT_FN (BUILT_IN_ASIN):
+    CASE_FLT_FN (BUILT_IN_ATAN):
+    CASE_FLT_FN (BUILT_IN_COS):
+    CASE_FLT_FN (BUILT_IN_SIGNIFICAND):
+    CASE_FLT_FN (BUILT_IN_SIN):
+    CASE_FLT_FN (BUILT_IN_SQRT):
+    CASE_FLT_FN (BUILT_IN_FMOD):
+    CASE_FLT_FN (BUILT_IN_REMAINDER):
+      return true;
+
+    default:
+      return false;
+    }
+}