Add a non-allocating version of fieldref

Similar to the commit for arrayref, a non-allocating version of fieldref
allows the static analyzer to know about these invariants.

src/ast.c

@@ -682,7 +682,7 @@ static value_t julia_to_scm_(fl_context_t *fl_ctx, jl_value_t *v)
  if (jl_typeis(v, jl_labelnode_type))
  return julia_to_list2(fl_ctx, (jl_value_t*)label_sym, jl_fieldref(v,0));
  if (jl_typeis(v, jl_linenumbernode_type)) {
- jl_value_t *file = jl_fieldref(v,1); // non-allocating
+ jl_value_t *file = jl_fieldref_noalloc(v,1); // non-allocating
  jl_value_t *line = jl_fieldref(v,0); // allocating
  value_t args = julia_to_list2(fl_ctx, line, file);
  fl_gc_handle(fl_ctx, &args);

src/codegen.cpp

@@ -3742,7 +3742,7 @@ static jl_cgval_t emit_expr(jl_codectx_t &ctx, jl_value_t *expr)
  if (!jl_is_expr(expr)) {
  int needroot = true;
  if (jl_is_quotenode(expr)) {
- expr = jl_fieldref(expr,0);
+ expr = jl_fieldref_noalloc(expr,0);
  }
  // numeric literals
  if (jl_is_int32(expr)) {

src/datatype.c

@@ -850,6 +850,15 @@ JL_DLLEXPORT jl_value_t *jl_get_nth_field(jl_value_t *v, size_t i)
  return jl_new_bits(ty, (char*)v + offs);
 }
 
+JL_DLLEXPORT jl_value_t *jl_get_nth_field_noalloc(jl_value_t *v JL_PROPAGATES_ROOT, size_t i) JL_NOTSAFEPOINT
+{
+ jl_datatype_t *st = (jl_datatype_t*)jl_typeof(v);
+ assert(i < jl_datatype_nfields(st));
+ size_t offs = jl_field_offset(st,i);
+ assert(jl_field_isptr(st,i));
+ return *(jl_value_t**)((char*)v + offs);
+}
+
 JL_DLLEXPORT jl_value_t *jl_get_nth_field_checked(jl_value_t *v, size_t i)
 {
  jl_datatype_t *st = (jl_datatype_t*)jl_typeof(v);

src/julia.h

@@ -775,6 +775,7 @@ STATIC_INLINE void jl_array_uint8_set(void *a, size_t i, uint8_t x)
 #define jl_expr_nargs(e) jl_array_len(((jl_expr_t*)(e))->args)
 
 #define jl_fieldref(s,i) jl_get_nth_field(((jl_value_t*)(s)),i)
+#define jl_fieldref_noalloc(s,i) jl_get_nth_field_noalloc(((jl_value_t*)(s)),i)
 #define jl_nfields(v) jl_datatype_nfields(jl_typeof(v))
 
 // Not using jl_fieldref to avoid allocations
@@ -1212,6 +1213,8 @@ STATIC_INLINE jl_vararg_kind_t jl_va_tuple_kind(jl_datatype_t *t)
 // structs
 JL_DLLEXPORT int jl_field_index(jl_datatype_t *t, jl_sym_t *fld, int err);
 JL_DLLEXPORT jl_value_t *jl_get_nth_field(jl_value_t *v, size_t i);
+// Like jl_get_nth_field above, but asserts if it needs to allocate
+JL_DLLEXPORT jl_value_t *jl_get_nth_field_noalloc(jl_value_t *v JL_PROPAGATES_ROOT, size_t i) JL_NOTSAFEPOINT;
 JL_DLLEXPORT jl_value_t *jl_get_nth_field_checked(jl_value_t *v, size_t i);
 JL_DLLEXPORT void jl_set_nth_field(jl_value_t *v, size_t i,
  jl_value_t *rhs);

src/rtutils.c

@@ -913,7 +913,7 @@ static size_t jl_static_show_x_(JL_STREAM *out, jl_value_t *v, jl_datatype_t *vt
  }
  if (vt == jl_typemap_entry_type) {
  n += jl_printf(out, ", next=↩︎\n ");
- n += jl_static_show_x(out, jl_fieldref(v, 0), depth);
+ n += jl_static_show_x(out, jl_fieldref_noalloc(v, 0), depth);
  }
  }
  n += jl_printf(out, ")");