Add support for Unsafe.BitCast to mono interp

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

@@ -2165,6 +2165,103 @@ interp_handle_intrinsics (TransformData *td, MonoMethod *target_method, MonoClas
 			return TRUE;
 		} else if (!strcmp (tm, "AreSame")) {
 			*op = MINT_CEQ_P;
+		} else if (!strcmp (tm, "BitCast")) {
+			MonoGenericContext *ctx = mono_method_get_context (target_method);
+			g_assert (ctx);
+			g_assert (ctx->method_inst);
+			g_assert (ctx->method_inst->type_argc == 2);
+			g_assert (csignature->param_count == 1);
+
+			// We explicitly do not handle gsharedvt as it is meant as a slow fallback strategy
+			// instead we fallback to the managed implementation which will do the right things
+
+			MonoType *tfrom = ctx->method_inst->type_argv [0];
+			if (mini_is_gsharedvt_variable_type (tfrom)) {
+				return FALSE;
+			}
+
+			MonoType *tto = ctx->method_inst->type_argv [1];
+			if (mini_is_gsharedvt_variable_type (tto)) {
+				return FALSE;
+			}
+
+			// The underlying API always throws for reference type inputs, so we
+			// fallback to the managed implementation to let that handling occur
+
+			MonoTypeEnum tfrom_type = tfrom->type;
+			if (MONO_TYPE_IS_REFERENCE (tfrom)) {
+				return FALSE;
+			}
+
+			MonoTypeEnum tto_type = tto->type;
+			if (MONO_TYPE_IS_REFERENCE (tto)) {
+				return FALSE;
+			}
+
+			MonoClass *tfrom_klass = mono_class_from_mono_type_internal (tfrom);
+			if (mono_class_is_nullable (tfrom_klass)) {
+				return FALSE;
+			}
+
+			// We also always throw for Nullable<T> inputs, so fallback to the
+			// managed implementation here as well.
+
+			MonoClass *tto_klass = mono_class_from_mono_type_internal (tto);
+			if (mono_class_is_nullable (tto_klass)) {
+				return FALSE;
+			}
+
+			// The same applies for when the type sizes do not match, as this will always throw
+			// and so its not an expected case and we can fallback to the managed implementation
+
+			int tfrom_align, tto_align;
+			if (mono_type_size (tfrom, &tfrom_align) != mono_type_size (tto, &tto_align)) {
+				return FALSE;
+			}
+
+			// We have several different move opcodes to handle the data depending on the
+			// source and target types, so detect and optimize the most common ones falling
+			// back to what is effectively `ReadUnaligned<TTo>(ref As<TFrom, byte>(ref source))`
+			// for anything that can't be special cased as potentially zero-cost move.
+
+			if (tfrom_type == MONO_TYPE_I4) {
+				if (tto_type == MONO_TYPE_R4) {
+					*op = MINT_BITCAST_R4_I4;
+				} else if (tto_type == MONO_TYPE_I4) {
+					*op = MINT_MOV_4;
+				}
+			} else if (tfrom_type == MONO_TYPE_I8) {
+				if (tto_type == MONO_TYPE_R8) {
+					*op = MINT_BITCAST_R8_I8;
+				} else if (tto_type == MONO_TYPE_I8) {
+					*op = MINT_MOV_8;
+				}
+			} else if (tfrom_type == MONO_TYPE_R4) {
+				if (tto_type == MONO_TYPE_I4) {
+					*op = MINT_BITCAST_I4_R4;
+				} else if (tto_type == MONO_TYPE_R4) {
+					*op = MINT_MOV_4;
+				}
+			} else if (tfrom_type == MONO_TYPE_R8) {
+				if (tto_type == MONO_TYPE_I8) {
+					*op = MINT_BITCAST_I8_R8;
+				} else if (tto_type == MONO_TYPE_R8) {
+					*op = MINT_MOV_8;
+				}
+			}
+
+			if (*op == -1) {
+				gint32 size = mono_class_value_size (tfrom_klass, NULL);
+				g_assert (size < G_MAXUINT16);
+
+				interp_add_ins (td, MINT_MOV_VT);
+				interp_ins_set_sreg (td->last_ins, td->sp [-1].var);
+				push_type_vt (td, tto_klass, size);
+				interp_ins_set_dreg (td->last_ins, td->sp [-1].var);
+				td->last_ins->data [0] = GINT32_TO_UINT16 (size);
+				td->ip++;
+				return TRUE;
+			}
 		} else if (!strcmp (tm, "ByteOffset")) {
 #if SIZEOF_VOID_P == 4
 			interp_add_ins (td, MINT_SUB_I4);

src/mono/mono/mini/mini-llvm.c

@@ -5757,23 +5757,12 @@ emit_handler_start (EmitContext *ctx, MonoBasicBlock *bb, LLVMBuilderRef builder
 static LLVMValueRef
 get_double_const (MonoCompile *cfg, double val)
 {
-	//#ifdef TARGET_WASM
-#if 0
-	//Wasm requires us to canonicalize NaNs.
-	if (mono_isnan (val))
-		*(gint64 *)&val = 0x7FF8000000000000ll;
-#endif
 	return LLVMConstReal (LLVMDoubleType (), val);
 }
 
 static LLVMValueRef
 get_float_const (MonoCompile *cfg, float val)
 {
-	//#ifdef TARGET_WASM
-#if 0
-	if (mono_isnan (val))
-		*(int *)&val = 0x7FC00000;
-#endif
 	return LLVMConstReal (LLVMFloatType (), val);
 }