re PR target/79027 (fold-const.c:11104:1: internal compiler error: Floating point exception)

	PR target/79027
	* config/pa/pa.c (pa_cannot_change_mode_class): Reject changes to/from
	modes with zero size.  Enhance comment.

From-SVN: r247869

gcc/ChangeLog

+2017-05-10  John David Anglin  <danglin@gcc.gnu.org>
+
+	PR target/79027
+	* config/pa/pa.c (pa_cannot_change_mode_class): Reject changes to/from
+	modes with zero size.  Enhance comment.
+
 2017-05-10  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
 
 	* config/rs6000/rs6000.c (altivec_init_builtins): Define POWER8

gcc/config/pa/pa.c

@@ -9962,19 +9962,23 @@ pa_cannot_change_mode_class (machine_mode from, machine_mode to,
   if (from == to)
     return false;
 
+  if (GET_MODE_SIZE (from) == GET_MODE_SIZE (to))
+    return false;
+
+  /* Reject changes to/from modes with zero size.  */
+  if (!GET_MODE_SIZE (from) || !GET_MODE_SIZE (to))
+    return true;
+
   /* Reject changes to/from complex and vector modes.  */
   if (COMPLEX_MODE_P (from) || VECTOR_MODE_P (from)
       || COMPLEX_MODE_P (to) || VECTOR_MODE_P (to))
     return true;
       
-  if (GET_MODE_SIZE (from) == GET_MODE_SIZE (to))
-    return false;
-
-  /* There is no way to load QImode or HImode values directly from
-     memory.  SImode loads to the FP registers are not zero extended.
-     On the 64-bit target, this conflicts with the definition of
-     LOAD_EXTEND_OP.  Thus, we can't allow changing between modes
-     with different sizes in the floating-point registers.  */
+  /* There is no way to load QImode or HImode values directly from memory
+     to a FP register.  SImode loads to the FP registers are not zero
+     extended.  On the 64-bit target, this conflicts with the definition
+     of LOAD_EXTEND_OP.  Thus, we can't allow changing between modes with
+     different sizes in the floating-point registers.  */
   if (MAYBE_FP_REG_CLASS_P (rclass))
     return true;