rs6000: Fix a mistake in cstore_si_as_di (PR68865, PR68879)

convert_move does not know how to zero-extend a constant integer to the
target mode -- simply because it does not know the source mode.  As a
result, 32-bit SImode with the high bit set would be effectively sign-
extended instead of zero-extended.

This patch fixes it.


	PR target/68865
	PR target/68879
	* config/rs6000/rs6000.md (cstore_si_as_di): Force all operands
	into registers.

From-SVN: r231621

gcc/ChangeLog

+2015-12-14  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR target/68865
+	PR target/68879
+	* config/rs6000/rs6000.md (cstore_si_as_di): Force all operands
+	into registers.
+
 2015-12-14  Richard Biener  <rguenther@suse.de>
 
 	Revert accidentially applied

gcc/config/rs6000/rs6000.md

@@ -10631,6 +10631,8 @@
   int uns_flag = unsigned_comparison_operator (operands[1], VOIDmode) ? 1 : 0;
   enum rtx_code cond_code = signed_condition (GET_CODE (operands[1]));
 
+  operands[2] = force_reg (SImode, operands[2]);
+  operands[3] = force_reg (SImode, operands[3]);
   rtx op1 = gen_reg_rtx (DImode);
   rtx op2 = gen_reg_rtx (DImode);
   convert_move (op1, operands[2], uns_flag);