[AArch64] Factor out pfalse predicate creation

Following on from the previous ptrue patch.

2019-06-18  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64-protos.h (aarch64_pfalse_reg): Declare.
	* config/aarch64/aarch64.c (aarch64_pfalse_reg): New function.
	* config/aarch64/aarch64-sve.md: Use it.

From-SVN: r272425

gcc/ChangeLog

 2019-06-18  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* config/aarch64/aarch64-protos.h (aarch64_pfalse_reg): Declare.
+	* config/aarch64/aarch64.c (aarch64_pfalse_reg): New function.
+	* config/aarch64/aarch64-sve.md: Use it.
+
+2019-06-18  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* config/aarch64/aarch64-protos.h (aarch64_ptrue_reg): Declare.
 	* config/aarch64/aarch64.c (aarch64_ptrue_reg): New functions.
 	(aarch64_expand_sve_widened_duplicate, aarch64_expand_sve_mem_move)

gcc/config/aarch64/aarch64-protos.h

@@ -521,6 +521,7 @@ void aarch64_err_no_fpadvsimd (machine_mode);
 void aarch64_expand_epilogue (bool);
 void aarch64_expand_mov_immediate (rtx, rtx, rtx (*) (rtx, rtx) = 0);
 rtx aarch64_ptrue_reg (machine_mode);
+rtx aarch64_pfalse_reg (machine_mode);
 void aarch64_emit_sve_pred_move (rtx, rtx, rtx);
 void aarch64_expand_sve_mem_move (rtx, rtx, machine_mode);
 bool aarch64_maybe_expand_sve_subreg_move (rtx, rtx);

gcc/config/aarch64/aarch64-sve.md

@@ -488,7 +488,7 @@
       {
 	/* The last element can be extracted with a LASTB and a false
 	   predicate.  */
-	rtx sel = force_reg (<VPRED>mode, CONST0_RTX (<VPRED>mode));
+	rtx sel = aarch64_pfalse_reg (<VPRED>mode);
 	emit_insn (gen_extract_last_<mode> (operands[0], sel, operands[1]));
 	DONE;
       }

gcc/config/aarch64/aarch64.c

@@ -2467,6 +2467,15 @@ aarch64_ptrue_reg (machine_mode mode)
   return force_reg (mode, CONSTM1_RTX (mode));
 }
 
+/* Return an all-false predicate register of mode MODE.  */
+
+rtx
+aarch64_pfalse_reg (machine_mode mode)
+{
+  gcc_assert (GET_MODE_CLASS (mode) == MODE_VECTOR_BOOL);
+  return force_reg (mode, CONST0_RTX (mode));
+}
+
 /* Return true if we can move VALUE into a register using a single
    CNT[BHWD] instruction.  */