Merge pull request #1785 from Unity-Technologies/unity-2023.1-mbe-fix-uum-27537

[2023.1][mono][jit] Emit a null check when storing to valuetype fields. (#82663)

Author: jhcdunity3d

mono/mini/ir-emit.h

@@ -881,6 +881,13 @@ static int ccount = 0;
 #define MONO_EMIT_NEW_IMPLICIT_EXCEPTION_LOAD_STORE(cfg) do { \
     } while (0)
 
+#define MONO_EMIT_EXPLICIT_NULL_CHECK(cfg, reg) do { \
+		cfg->flags |= MONO_CFG_HAS_CHECK_THIS; \
+		MONO_EMIT_NEW_BIALU_IMM (cfg, OP_COMPARE_IMM, -1, (reg), 0);	\
+		MONO_EMIT_NEW_COND_EXC (cfg, EQ, "NullReferenceException");		\
+		MONO_EMIT_NEW_UNALU (cfg, OP_NOT_NULL, -1, reg); \
+	} while (0)
+
 /* Emit an explicit null check which doesn't depend on SIGSEGV signal handling */
 #define MONO_EMIT_NULL_CHECK(cfg, reg, out_of_page) do { \
 		if (cfg->explicit_null_checks || (out_of_page)) {							  \

mono/mini/method-to-ir.c

@@ -9661,6 +9661,10 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 							EMIT_NEW_BIALU_IMM (cfg, ptr, OP_PADD_IMM, dreg, sp [0]->dreg, foffset);
 							store = mini_emit_storing_write_barrier (cfg, ptr, sp [1]);
 						} else {
+							if (MONO_TYPE_ISSTRUCT (field->type))
+								/* The decomposition might end up calling a copy/wbarrier function which doesn't do null checks */
+								MONO_EMIT_EXPLICIT_NULL_CHECK (cfg, sp [0]->dreg);
+
 							EMIT_NEW_STORE_MEMBASE_TYPE (cfg, store, field->type, sp [0]->dreg, foffset, sp [1]->dreg);
 						}
 					}