re PR tree-optimization/88074 (g++ hangs on math expression)

2019-02-19  Richard Biener  <rguenther@suse.de>

        PR middle-end/88074
	* toplev.c (do_compile): Initialize mpfr's exponent range
	based on available float modes.

	* gcc.dg/pr88074.c: New testcase.

From-SVN: r269015

gcc/ChangeLog

+2019-02-19  Richard Biener  <rguenther@suse.de>
+
+        PR middle-end/88074
+	* toplev.c (do_compile): Initialize mpfr's exponent range
+	based on available float modes.
+
 2019-02-19  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* rtlanal.c (get_initial_register_offset): Fall back to the estimate

gcc/testsuite/ChangeLog

+2019-02-19  Richard Biener  <rguenther@suse.de>
+
+        PR middle-end/88074
+	* gcc.dg/pr88074.c: New testcase.
+
 2019-02-19  Jakub Jelinek  <jakub@redhat.com>
 
 	PR middle-end/89303

gcc/testsuite/gcc.dg/pr88074.c

+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+#include <complex.h>
+
+int main()
+{
+  _Complex double x;
+  __real x = 3.091e+8;
+  __imag x = -4.045e+8;
+  /* This used to spend huge amounts of compile-time inside mpc.  */
+  volatile _Complex double y = ctan (x);
+  return 0;
+}

gcc/toplev.c

@@ -2153,6 +2153,30 @@ do_compile ()
 	else
 	  int_n_enabled_p[i] = false;
 
+      /* Initialize mpfrs exponent range.  This is important to get
+         underflow/overflow in a reasonable timeframe.  */
+      machine_mode mode;
+      int min_exp = -1;
+      int max_exp = 1;
+      FOR_EACH_MODE_IN_CLASS (mode, MODE_FLOAT)
+	if (SCALAR_FLOAT_MODE_P (mode))
+	  {
+	    const real_format *fmt = REAL_MODE_FORMAT (mode);
+	    if (fmt)
+	      {
+		/* fmt->emin - fmt->p + 1 should be enough but the
+		   back-and-forth dance in real_to_decimal_for_mode we
+		   do for checking fails due to rounding effects then.  */
+		if ((fmt->emin - fmt->p) < min_exp)
+		  min_exp = fmt->emin - fmt->p;
+		if (fmt->emax > max_exp)
+		  max_exp = fmt->emax;
+	      }
+	  }
+      if (mpfr_set_emin (min_exp)
+	  || mpfr_set_emax (max_exp))
+	sorry ("mpfr not configured to handle all float modes");
+
       /* Set up the back-end if requested.  */
       if (!no_backend)
 	backend_init ();