[release/9.0-staging] [mono][interp] Minor SSA fixes (#116428)

* [mono][interp] Add possibility to configure interp options from env var

* [mono][interp] Update var definition when inserting new instructions during cprop (#116179)

The definition was not updated, leading to invalid optimizations later on.

* [mono][interp] Fix broken code attempting to reapply superinstruction optimization (#116069)

For each instruction in a basic block we check for patterns. In a certain case, once we replaced the instruction with a new one, we were attempting to do a loop reiteration by setting `ins = ins->prev` so after the loop reincrements with `ins = ins->next` we check super instruction patterns again for the current instruction. This is broken if `ins` was the first instruction in a basic block, aka `ins->prev` is NULL. This used to be impossible before SSA optimizations, since super instruction pass was applying optimizations in a single basic block only.

Author: BrzVlad

src/mono/mono/mini/interp/interp.c

@@ -8981,6 +8981,10 @@ mono_ee_interp_init (const char *opts)
 	set_context (NULL);
 
 	interp_parse_options (opts);
+
+	const char *env_opts = g_getenv ("MONO_INTERPRETER_OPTIONS");
+	if (env_opts)
+		interp_parse_options (env_opts);
 	/* Don't do any optimizations if running under debugger */
 	if (mini_get_debug_options ()->mdb_optimizations)
 		mono_interp_opt = 0;

src/mono/mono/mini/interp/transform-opt.c

@@ -3124,6 +3124,7 @@ interp_cprop (TransformData *td)
 						ins->data [2] = GINT_TO_UINT16 (ldsize);
 
 						interp_clear_ins (ins->prev);
+						td->var_values [ins->dreg].def = ins;
 					}
 					if (td->verbose_level) {
 						g_print ("Replace ldloca/ldobj_vt pair :\n\t");
@@ -3204,6 +3205,7 @@ interp_cprop (TransformData *td)
 						ins->data [2] = vtsize;
 
 						interp_clear_ins (ins->prev);
+						td->var_values [ins->dreg].def = ins;
 
 						// MINT_MOV_DST_OFF doesn't work if dreg is allocated at the same location as the
 						// field value to be stored, because its behavior is not atomic in nature. We first
@@ -3400,9 +3402,11 @@ interp_super_instructions (TransformData *td)
 		current_liveness.bb_dfs_index = bb->dfs_index;
 		current_liveness.ins_index = 0;
 		for (InterpInst *ins = bb->first_ins; ins != NULL; ins = ins->next) {
-			int opcode = ins->opcode;
+			int opcode;
 			if (bb->dfs_index >= td->bblocks_count_no_eh || bb->dfs_index == -1 || (ins->flags & INTERP_INST_FLAG_LIVENESS_MARKER))
 				current_liveness.ins_index++;
+retry_ins:
+			opcode = ins->opcode;
 			if (MINT_IS_NOP (opcode))
 				continue;
 
@@ -3801,9 +3805,7 @@ interp_super_instructions (TransformData *td)
 								g_print ("superins: ");
 								interp_dump_ins (ins, td->data_items);
 							}
-							// The newly added opcode could be part of further superinstructions. Retry
-							ins = ins->prev;
-							continue;
+							goto retry_ins;
 						}
 					}
 				}