[jit] Optimize ldloc+ldfld operations for valuetypes, so they don't require...

[jit] Optimize ldloc+ldfld operations for valuetypes, so they don't require making a copy of the valuetype. Hopefully fixes #56452. (#5166)

mono/mini/method-to-ir.c

@@ -7829,7 +7829,12 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 			CHECK_STACK_OVF (1);
 			n = ip [1];
 			CHECK_LOCAL (n);
-			EMIT_NEW_LOCLOAD (cfg, ins, n);
+			if ((ip [2] == CEE_LDFLD) && ip_in_bb (cfg, cfg->cbb, ip + 2) && MONO_TYPE_ISSTRUCT (header->locals [n])) {
+				/* Avoid loading a struct just to load one of its fields */
+				EMIT_NEW_LOCLOADA (cfg, ins, n);
+			} else {
+				EMIT_NEW_LOCLOAD (cfg, ins, n);
+			}
 			*sp++ = ins;
 			ip += 2;
 			break;
@@ -12284,7 +12289,12 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 				CHECK_OPSIZE (4);
 				n = read16 (ip + 2);
 				CHECK_LOCAL (n);
-				EMIT_NEW_LOCLOAD (cfg, ins, n);
+				if ((ip [4] == CEE_LDFLD) && ip_in_bb (cfg, cfg->cbb, ip + 4) && header->locals [n]->type == MONO_TYPE_VALUETYPE) {
+					/* Avoid loading a struct just to load one of its fields */
+					EMIT_NEW_LOCLOADA (cfg, ins, n);
+				} else {
+					EMIT_NEW_LOCLOAD (cfg, ins, n);
+				}
 				*sp++ = ins;
 				ip += 4;
 				break;