rs6000: Merge the var_shift yes/no alternatives

All instructions that are "var_shift" for some alternative have the shift
amount as operands[2].

This patch introduces an attribute "maybe_var_shift".  If that is set to
"yes", the default value of "var_shift" is set based on the operands[2]
value.

With that, we can merge the var_shift yes/no cases everywhere.  Do so.

Also change some more "i" to "n".

From-SVN: r211880

gcc/ChangeLog

@@ -1,3 +1,25 @@
+2014-06-22  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	* config/rs6000/rs6000.md (maybe_var_shift): New define_attr.
+	(var_shift): Use it.
+	(rotl<mode>3, *rotlsi3_64, *rotl<mode>3_dot, *rotl<mode>3_dot2,
+	*rotlsi3_internal4, *rotlsi3_internal5, *rotlsi3_internal6,
+	*rotlsi3_internal8le, *rotlsi3_internal8be, *rotlsi3_internal9le,
+	*rotlsi3_internal9be, *rotlsi3_internal10le, *rotlsi3_internal10be,
+	*rotlsi3_internal11le, *rotlsi3_internal11be, *rotlsi3_internal12le,
+	*rotlsi3_internal12be, ashl<mode>3, *ashlsi3_64, *ashl<mode>3_dot,
+	*ashl<mode>3_dot2, lshr<mode>3, *lshrsi3_64, *lshr<mode>3_dot,
+	*lshr<mode>3_dot2, *ashr<mode>3, *ashrsi3_64, *ashr<mode>3_dot,
+	*ashr<mode>3_dot2, *rotldi3_internal4, *rotldi3_internal5,
+	*rotldi3_internal6, *rotldi3_internal7le, *rotldi3_internal7be,
+	*rotldi3_internal8le, *rotldi3_internal8be, *rotldi3_internal9le,
+	*rotldi3_internal9be, *rotldi3_internal10le, *rotldi3_internal10be,
+	*rotldi3_internal11le, *rotldi3_internal11be, *rotldi3_internal12le,
+	*rotldi3_internal12be, *rotldi3_internal13le, *rotldi3_internal13be,
+	*rotldi3_internal14le, *rotldi3_internal14be, *rotldi3_internal15le,
+	*rotldi3_internal15be): Use the new attribute.  Merge register and
+	integer alternatives.
+
 2014-06-22  Segher Boessenkool  <segher@kernel.crashing.org>
 
 	* config/rs6000/rs6000.md (ashrsi3, two anonymous define_insns and