Refuse to inline with arg op after deopt op

We cannot restore the args buffer and parameter context properly when we
uninline such a frame, which can then cause a crash after the deopt. In
theory this has long been a possible problem, however the new derived
specializations make it more likely to happen - though possibly only
because we are making poor decisions about what to guard on.

src/spesh/inline.c

@@ -105,6 +105,7 @@ static int is_graph_inlineable(MVMThreadContext *tc, MVMSpeshGraph *inliner,
     MVMSpeshBB *bb = ig->entry;
     MVMint32 same_hll = target_sf->body.cu->body.hll_config ==
             inliner->sf->body.cu->body.hll_config;
+    MVMuint32 seen_possible_deopt = 0;
     if (no_inline_info)
         *no_inline_info = NULL;
     while (bb) {
@@ -161,7 +162,9 @@ static int is_graph_inlineable(MVMThreadContext *tc, MVMSpeshGraph *inliner,
                 }
             }
 
-            /* Check we don't have too many args for inlining to work out. */
+            /* Check we don't have too many args for inlining to work out,
+             * and that we're not reading args after a possible deopt
+             * instruction, because we can't uninline in such a case. */
             else if (opcode == MVM_OP_sp_getarg_o ||
                     opcode == MVM_OP_sp_getarg_i ||
                     opcode == MVM_OP_sp_getarg_n ||
@@ -170,6 +173,10 @@ static int is_graph_inlineable(MVMThreadContext *tc, MVMSpeshGraph *inliner,
                     *no_inline_reason = "too many arguments to inline";
                     return 0;
                 }
+                if (seen_possible_deopt) {
+                    *no_inline_reason = "a deopt may happen before arguments are processed";
+                    return 0;
+                }
             }
 
             /* Ext-ops need special care in inter-comp-unit inlines. */
@@ -180,6 +187,10 @@ static int is_graph_inlineable(MVMThreadContext *tc, MVMSpeshGraph *inliner,
                     demand_extop(tc, target_cu, source_cu, ins->info);
             }
 
+            /* Record if this instruction would cause us to deopt. */
+            if (ins->info->may_cause_deopt)
+                seen_possible_deopt = 1;
+
             ins = ins->next;
         }
         bb = bb->linear_next;