[mono] Add unchecked version of stelem_ref interpreter opcode (#99829)

* Introduce mint_stelem_ref_unchecked
* Inline most of stelem_ref_unchecked in jiterpreter traces
* Add more complete type check for stelem_ref_unchecked
* Correctness fix and simplification for stelem_ref_unchecked

Author: kg

src/mono/browser/runtime/jiterpreter-trace-generator.ts

@@ -3347,13 +3347,21 @@ function emit_arrayop (builder: WasmBuilder, frame: NativePointer, ip: MintOpcod
             append_ldloc(builder, getArgU16(ip, 2), WasmOpcode.i32_load);
             // value
             append_ldloc(builder, getArgU16(ip, 3), WasmOpcode.i32_load);
-            builder.callImport("stelem_ref");
+            builder.callImport("stelemr_tc");
             builder.appendU8(WasmOpcode.br_if);
             builder.appendULeb(0);
             append_bailout(builder, ip, BailoutReason.ArrayStoreFailed);
             builder.endBlock();
             return true;
         }
+        case MintOpcode.MINT_STELEM_REF_UNCHECKED: {
+            // dest
+            append_getelema1(builder, ip, objectOffset, indexOffset, 4);
+            // &value (src)
+            append_ldloca(builder, valueOffset, 0);
+            builder.callImport("copy_ptr");
+            return true;
+        }
         case MintOpcode.MINT_LDELEM_REF:
             elementSize = 4;
             elementGetter = WasmOpcode.i32_load;

src/mono/browser/runtime/jiterpreter.ts

@@ -285,7 +285,7 @@ function getTraceImports () {
         importDef("stfld_o", getRawCwrap("mono_jiterp_set_object_field")),
         importDef("cmpxchg_i32", getRawCwrap("mono_jiterp_cas_i32")),
         importDef("cmpxchg_i64", getRawCwrap("mono_jiterp_cas_i64")),
-        importDef("stelem_ref", getRawCwrap("mono_jiterp_stelem_ref")),
+        ["stelemr_tc", "stelemr", getRawCwrap("mono_jiterp_stelem_ref")],
         importDef("fma", getRawCwrap("fma")),
         importDef("fmaf", getRawCwrap("fmaf")),
     ];
@@ -649,7 +649,7 @@ function initialize_builder (builder: WasmBuilder) {
         WasmValtype.void, true
     );
     builder.defineType(
-        "stelem_ref",
+        "stelemr",
         {
             "o": WasmValtype.i32,
             "aindex": WasmValtype.i32,

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

@@ -6660,6 +6660,14 @@ MINT_IN_CASE(MINT_BRTRUE_I8_SP) ZEROP_SP(gint64, !=); MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STELEM_I8) STELEM(gint64, gint64); MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STELEM_R4) STELEM(float, float); MINT_IN_BREAK;
 		MINT_IN_CASE(MINT_STELEM_R8) STELEM(double, double); MINT_IN_BREAK;
+		MINT_IN_CASE(MINT_STELEM_REF_UNCHECKED) {
+			MonoArray *o;
+			guint32 aindex;
+			STELEM_PROLOG(o, aindex);
+			mono_array_setref_fast ((MonoArray *) o, aindex, LOCAL_VAR (ip [3], MonoObject*));
+			ip += 4;
+			MINT_IN_BREAK;
+		}
 		MINT_IN_CASE(MINT_STELEM_REF) {
 			MonoArray *o;
 			guint32 aindex;
@@ -6676,7 +6684,6 @@ MINT_IN_CASE(MINT_BRTRUE_I8_SP) ZEROP_SP(gint64, !=); MINT_IN_BREAK;
 			ip += 4;
 			MINT_IN_BREAK;
 		}
-
 		MINT_IN_CASE(MINT_STELEM_VT) {
 			MonoArray *o = LOCAL_VAR (ip [1], MonoArray*);
 			NULL_CHECK (o);

src/mono/mono/mini/interp/mintops.def

@@ -413,6 +413,7 @@ OPDEF(MINT_STELEM_R8, "stelem.r8", 4, 0, 3, MintOpNoArgs)
 OPDEF(MINT_STELEM_REF, "stelem.ref", 4, 0, 3, MintOpNoArgs)
 OPDEF(MINT_STELEM_VT, "stelem.vt", 6, 0, 3, MintOpTwoShorts)
 OPDEF(MINT_STELEM_VT_NOREF, "stelem.vt.noref", 6, 0, 3, MintOpTwoShorts)
+OPDEF(MINT_STELEM_REF_UNCHECKED, "stelem.ref.unchecked", 4, 0, 3, MintOpNoArgs)
 
 OPDEF(MINT_LDLEN, "ldlen", 3, 1, 1, MintOpNoArgs)
 

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

@@ -4945,6 +4945,35 @@ handle_stelem (TransformData *td, int op)
 	interp_add_ins (td, op);
 	td->sp -= 3;
 	interp_ins_set_sregs3 (td->last_ins, td->sp [0].var, td->sp [1].var, td->sp [2].var);
+
+	if (op == MINT_STELEM_REF) {
+		InterpVar *array_var = &td->vars [td->last_ins->sregs [0]],
+			*value_var = &td->vars [td->last_ins->sregs [2]];
+		MonoClass *array_var_klass = mono_class_from_mono_type_internal (array_var->type),
+			*value_var_klass = mono_class_from_mono_type_internal (value_var->type);
+
+		if (m_class_is_array (array_var_klass)) {
+			MonoClass *array_element_klass = m_class_get_element_class (array_var_klass);
+			// If lhs is T[] and rhs is T and T is sealed, we can skip the runtime typecheck
+			if (
+				(array_element_klass == value_var_klass) &&
+				m_class_is_sealed(value_var_klass) &&
+				// HACK: Arrays are sealed, but it's possible to downcast string[][] to object[][],
+				//  so we don't want to treat elements of array types as actually sealed.
+				// Our lhs of type object[][] might actually be of a different reference type.
+				!m_class_is_array(value_var_klass)
+			){
+				if (td->verbose_level > 2)
+					g_printf (
+						"MINT_STELEM_REF_UNCHECKED for %s in %s::%s\n",
+						m_class_get_name (value_var_klass),
+						m_class_get_name (td->method->klass), td->method->name
+					);
+				td->last_ins->opcode = MINT_STELEM_REF_UNCHECKED;
+			}
+		}
+	}
+
 	++td->ip;
 }