turn guard(type|conc) into guardjust(type|conc)

if the facts support it, i.e. if the register is
known to contain the right type already.

src/spesh/optimize.c

@@ -741,6 +741,22 @@ static void optimize_guard(MVMThreadContext *tc, MVMSpeshGraph *g, MVMSpeshBB *b
 
         ins->info = MVM_op_get_op(MVM_OP_set);
     }
+    else if ((opcode == MVM_OP_sp_guardconc || opcode == MVM_OP_sp_guardtype) && can_drop_type_guard) {
+        MVM_spesh_graph_add_comment(tc, g, ins, "%s r%d(%d) r%d(%d); flags 0x%x",
+                ins->info->name,
+                ins->operands[0].reg.orig,
+                ins->operands[0].reg.i,
+                ins->operands[1].reg.orig,
+                ins->operands[1].reg.i,
+                facts->flags);
+
+        ins->operands[2] = ins->operands[3];
+        if (opcode == MVM_OP_sp_guardconc)
+            ins->info = MVM_op_get_op(MVM_OP_sp_guardjustconc);
+        else {
+            ins->info = MVM_op_get_op(MVM_OP_sp_guardjusttype);
+        }
+    }
 }
 
 static void optimize_can_op(MVMThreadContext *tc, MVMSpeshGraph *g, MVMSpeshBB *bb, MVMSpeshIns *ins) {