[rs6000] Use gen_int_mode in ieee_128bit_negative_zero

Previously we'd generate a non-canonical zero-extended CONST_INT
instead of a sign-extended one, which tripped the assert for
canonical CONST_INTs after a later patch.

2017-12-28  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* config/powerpcspe/powerpcspe.md (ieee_128bit_negative_zero): Use
	gen_int_mode rather than GEN_INT.
	* config/rs6000/rs6000.md (ieee_128bit_negative_zero): Likewise.

From-SVN: r256024

gcc/ChangeLog

 2017-12-28  Richard Sandiford  <richard.sandiford@linaro.org>
 
+	* config/powerpcspe/powerpcspe.md (ieee_128bit_negative_zero): Use
+	gen_int_mode rather than GEN_INT.
+	* config/rs6000/rs6000.md (ieee_128bit_negative_zero): Likewise.
+
+2017-12-28  Richard Sandiford  <richard.sandiford@linaro.org>
+
 	* emit-rtl.c (gen_const_vec_series): Use valid_for_const_vector_p
 	instead of CONSTANT_P.
 	(gen_vec_series): Likewise.

gcc/config/powerpcspe/powerpcspe.md

@@ -8113,7 +8113,7 @@
     RTVEC_ELT (v, i) = const0_rtx;
 
   high = (BYTES_BIG_ENDIAN) ? 0 : 15;
-  RTVEC_ELT (v, high) = GEN_INT (0x80);
+  RTVEC_ELT (v, high) = gen_int_mode (0x80, QImode);
 
   rs6000_expand_vector_init (operands[0], gen_rtx_PARALLEL (V16QImode, v));
   DONE;

gcc/config/rs6000/rs6000.md

@@ -8055,7 +8055,7 @@
     RTVEC_ELT (v, i) = const0_rtx;
 
   high = (BYTES_BIG_ENDIAN) ? 0 : 15;
-  RTVEC_ELT (v, high) = GEN_INT (0x80);
+  RTVEC_ELT (v, high) = gen_int_mode (0x80, QImode);
 
   rs6000_expand_vector_init (operands[0], gen_rtx_PARALLEL (V16QImode, v));
   DONE;