RISC-V: Do not allow v0 as dest when merging [PR115068].

This patch splits the vfw...wf pattern so we do not emit e.g. vfwadd.wf
v0,v8,fa5,v0.t anymore.

gcc/ChangeLog:

	PR target/115068

	* config/riscv/vector.md:  Split vfw<insn>.wf pattern.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/base/pr115068-run.c: New test.
	* gcc.target/riscv/rvv/base/pr115068.c: New test.

(cherry picked from commit a2fd081)

gcc/config/riscv/vector.md

@@ -7197,24 +7197,24 @@
 	(symbol_ref "riscv_vector::get_frm_mode (operands[9])"))])
 
 (define_insn "@pred_single_widen_<plus_minus:optab><mode>_scalar"
-  [(set (match_operand:VWEXTF 0 "register_operand"                   "=vr,   vr")
+  [(set (match_operand:VWEXTF 0 "register_operand"                "=vd, vd, vr, vr")
 	(if_then_else:VWEXTF
 	  (unspec:<VM>
-	    [(match_operand:<VM> 1 "vector_mask_operand"           "vmWc1,vmWc1")
-	     (match_operand 5 "vector_length_operand"              "   rK,   rK")
-	     (match_operand 6 "const_int_operand"                  "    i,    i")
-	     (match_operand 7 "const_int_operand"                  "    i,    i")
-	     (match_operand 8 "const_int_operand"                  "    i,    i")
-	     (match_operand 9 "const_int_operand"                  "    i,    i")
+	    [(match_operand:<VM> 1 "vector_mask_operand"          " vm, vm,Wc1,Wc1")
+	     (match_operand 5 "vector_length_operand"             " rK, rK, rK, rK")
+	     (match_operand 6 "const_int_operand"                 "  i,  i,  i,  i")
+	     (match_operand 7 "const_int_operand"                 "  i,  i,  i,  i")
+	     (match_operand 8 "const_int_operand"                 "  i,  i,  i,  i")
+	     (match_operand 9 "const_int_operand"                 "  i,  i,  i,  i")
 	     (reg:SI VL_REGNUM)
 	     (reg:SI VTYPE_REGNUM)
 	     (reg:SI FRM_REGNUM)] UNSPEC_VPREDICATE)
 	  (plus_minus:VWEXTF
-	    (match_operand:VWEXTF 3 "register_operand"             "   vr,   vr")
+	    (match_operand:VWEXTF 3 "register_operand"            " vr, vr, vr, vr")
 	    (float_extend:VWEXTF
 	      (vec_duplicate:<V_DOUBLE_TRUNC>
-		(match_operand:<VSUBEL> 4 "register_operand"       "    f,    f"))))
-	  (match_operand:VWEXTF 2 "vector_merge_operand"           "   vu,    0")))]
+		(match_operand:<VSUBEL> 4 "register_operand"      "  f,  f,  f,  f"))))
+	  (match_operand:VWEXTF 2 "vector_merge_operand"          " vu,  0, vu,  0")))]
   "TARGET_VECTOR"
   "vfw<insn>.wf\t%0,%3,%4%p1"
   [(set_attr "type" "vf<widen_binop_insn_type>")

gcc/testsuite/gcc.target/riscv/rvv/base/pr115068-run.c

@@ -0,0 +1,28 @@
+/* { dg-do run } */
+/* { dg-require-effective-target riscv_v_ok } */
+/* { dg-add-options riscv_v } */
+/* { dg-additional-options "-std=gnu99" } */
+
+#include <stdint.h>
+#include <riscv_vector.h>
+
+vfloat64m8_t
+test_vfwadd_wf_f64m8_m (vbool8_t vm, vfloat64m8_t vs2, float rs1, size_t vl)
+{
+  return __riscv_vfwadd_wf_f64m8_m (vm, vs2, rs1, vl);
+}
+
+char global_memory[1024];
+void *fake_memory = (void *) global_memory;
+
+int
+main ()
+{
+  asm volatile ("fence" ::: "memory");
+  vfloat64m8_t vfwadd_wf_f64m8_m_vd = test_vfwadd_wf_f64m8_m (
+    __riscv_vreinterpret_v_i8m1_b8 (__riscv_vundefined_i8m1 ()),
+    __riscv_vundefined_f64m8 (), 1.0, __riscv_vsetvlmax_e64m8 ());
+  asm volatile ("" ::"vr"(vfwadd_wf_f64m8_m_vd) : "memory");
+
+  return 0;
+}

gcc/testsuite/gcc.target/riscv/rvv/base/pr115068.c

@@ -0,0 +1,29 @@
+/* { dg-do compile } */
+/* { dg-add-options riscv_v } */
+/* { dg-additional-options "-std=gnu99" } */
+
+#include <stdint.h>
+#include <riscv_vector.h>
+
+vfloat64m8_t
+test_vfwadd_wf_f64m8_m (vbool8_t vm, vfloat64m8_t vs2, float rs1, size_t vl)
+{
+  return __riscv_vfwadd_wf_f64m8_m (vm, vs2, rs1, vl);
+}
+
+char global_memory[1024];
+void *fake_memory = (void *) global_memory;
+
+int
+main ()
+{
+  asm volatile ("fence" ::: "memory");
+  vfloat64m8_t vfwadd_wf_f64m8_m_vd = test_vfwadd_wf_f64m8_m (
+    __riscv_vreinterpret_v_i8m1_b8 (__riscv_vundefined_i8m1 ()),
+    __riscv_vundefined_f64m8 (), 1.0, __riscv_vsetvlmax_e64m8 ());
+  asm volatile ("" ::"vr"(vfwadd_wf_f64m8_m_vd) : "memory");
+
+  return 0;
+}
+
+/* { dg-final { scan-assembler-not "vfwadd.wf\tv0.*v0" } } */