Use `intrinsics.alloca` rather than `context.temp_allocator` in `json.unmarshal_object`

core/encoding/json/unmarshal.odin

@@ -6,6 +6,7 @@ import "core:reflect"
 import "core:strconv"
 import "core:strings"
 import "base:runtime"
+import "base:intrinsics"
 
 Unmarshal_Data_Error :: enum {
 	Invalid_Data,
@@ -368,11 +369,14 @@ unmarshal_object :: proc(p: ^Parser, v: any, end_token: Token_Kind) -> (err: Unm
 			unmarshal_expect_token(p, .Colon)						
 			
 			fields := reflect.struct_fields_zipped(ti.id)
-			
-			runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD(ignore = context.temp_allocator == context.allocator)
 
-			field_used := make([]bool, len(fields), context.temp_allocator)
+			field_test :: #force_inline proc "contextless" (field_used: [^]byte, index: int) -> bool {
+				prev_set := field_used[index/8] & byte(index&7) != 0
+				field_used[index/8] |= byte(index&7)
+				return prev_set
+			}
 			
+			field_used := intrinsics.alloca((len(fields)+7)/8, 1)
 			use_field_idx := -1
 			
 			for field, field_idx in fields {
@@ -393,10 +397,9 @@ unmarshal_object :: proc(p: ^Parser, v: any, end_token: Token_Kind) -> (err: Unm
 			}
 			
 			if use_field_idx >= 0 {
-				if field_used[use_field_idx] {
+				if field_test(field_used, use_field_idx) {
 					return .Multiple_Use_Field
 				}
-				field_used[use_field_idx] = true
 				offset := fields[use_field_idx].offset
 				type := fields[use_field_idx].type
 				name := fields[use_field_idx].name