Fix bogus CONST_WIDE_INT hash

The CONST_WIDE_INT case in const_rtx_hash_1 started the hash
with the precision of the mode, but the mode is always VOIDmode.

2017-08-21  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* varasm.c (const_rtx_hash_1): Don't hash in the mode of a
	CONST_WIDE_INT.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r251218

gcc/ChangeLog

+2017-08-21  Richard Sandiford  <richard.sandiford@linaro.org>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
+	* varasm.c (const_rtx_hash_1): Don't hash in the mode of a
+	CONST_WIDE_INT.
+
 2017-08-21  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/81884

gcc/varasm.c

@@ -3639,7 +3639,7 @@ const_rtx_hash_1 (const_rtx x)
       break;
 
     case CONST_WIDE_INT:
-      hwi = GET_MODE_PRECISION (mode);
+      hwi = 0;
       {
 	for (i = 0; i < CONST_WIDE_INT_NUNITS (x); i++)
 	  hwi ^= CONST_WIDE_INT_ELT (x, i);