Emit the correct kind of error for an eliminated getfield

I meant to do this when I implemented the codegen, but looks like
that never happened. We use a special symbol (##getfield##) to
indicate that an error is an UndefRefError rather than an
UndefVarError. Otherwise however, we use the same machinery
as undef var errors.

base/compiler/ssair/passes.jl

@@ -662,9 +662,9 @@ function getfield_elim_pass!(ir::IRCode, domtree)
  # Insert the undef check if necessary
  if any_undef && !is_unchecked
  if val === nothing
- insert_node!(compact, SSAValue(idx), Nothing, Expr(:throw_undef_if_not, :getfield, false))
+ insert_node!(compact, SSAValue(idx), Nothing, Expr(:throw_undef_if_not, Symbol("##getfield##"), false))
  else
- insert_node!(compact, SSAValue(idx), Nothing, Expr(:undefcheck, :getfield, val.x))
+ insert_node!(compact, SSAValue(idx), Nothing, Expr(:undefcheck, Symbol("##getfield##"), val.x))
  end
  else
  @assert val !== nothing

src/ast.c

@@ -67,7 +67,7 @@ jl_sym_t *macrocall_sym; jl_sym_t *colon_sym;
 jl_sym_t *hygienicscope_sym;
 jl_sym_t *escape_sym;
 jl_sym_t *gc_preserve_begin_sym; jl_sym_t *gc_preserve_end_sym;
-jl_sym_t *throw_undef_if_not_sym;
+jl_sym_t *throw_undef_if_not_sym; jl_sym_t *getfield_undefref_sym;
 
 static uint8_t flisp_system_image[] = {
 #include <julia_flisp.boot.inc>
@@ -392,6 +392,7 @@ void jl_init_frontend(void)
  generated_sym = jl_symbol("generated");
  generated_only_sym = jl_symbol("generated_only");
  throw_undef_if_not_sym = jl_symbol("throw_undef_if_not");
+ getfield_undefref_sym = jl_symbol("##getfield##");
  do_sym = jl_symbol("do");
 }
 

src/codegen.cpp

@@ -3928,8 +3928,14 @@ static jl_cgval_t emit_expr(jl_codectx_t &ctx, jl_value_t *expr, ssize_t ssaval)
  return emit_isdefined(ctx, args[0]);
  }
  else if (head == throw_undef_if_not_sym) {
- Value *cond = emit_unbox(ctx, T_int8, emit_expr(ctx, args[1]), (jl_value_t*)jl_bool_type);
- undef_var_error_ifnot(ctx, ctx.builder.CreateTrunc(cond, T_int1), (jl_sym_t*)args[0]);
+ jl_sym_t *var = (jl_sym_t*)args[0];
+ Value *cond = ctx.builder.CreateTrunc(emit_unbox(ctx, T_int8, emit_expr(ctx, args[1]), (jl_value_t*)jl_bool_type), T_int1);
+ if (var == getfield_undefref_sym) {
+ raise_exception_unless(ctx, cond,
+ literal_pointer_val(ctx, jl_undefref_exception));
+ } else {
+ undef_var_error_ifnot(ctx, cond, var);
+ }
  return ghostValue(jl_void_type);
  }
  else if (head == invoke_sym) {

src/interpreter.c

@@ -466,7 +466,11 @@ SECT_INTERP static jl_value_t *eval_value(jl_value_t *e, interpreter_state *s)
  jl_value_t *cond = eval_value(args[1], s);
  assert(jl_is_bool(cond));
  if (cond == jl_false) {
- jl_undefined_var_error((jl_sym_t*)args[0]);
+ jl_sym_t *var = (jl_sym_t*)args[0];
+ if (var == getfield_undefref_sym)
+ jl_throw(jl_undefref_exception);
+ else
+ jl_undefined_var_error(var);
  }
  return jl_nothing;
  }

src/julia_internal.h

@@ -973,6 +973,7 @@ extern jl_sym_t *gc_preserve_begin_sym; extern jl_sym_t *gc_preserve_end_sym;
 extern jl_sym_t *generated_sym;
 extern jl_sym_t *generated_only_sym;
 extern jl_sym_t *throw_undef_if_not_sym;
+extern jl_sym_t *getfield_undefref_sym;
 
 struct _jl_sysimg_fptrs_t;
 

test/core.jl

@@ -6267,3 +6267,6 @@ get27770(n::Nullable27770, v::Handle27770) = n.hasvalue ? n.value : v
 
 foo27770() = get27770(Nullable27770(), Handle27770())
 @test foo27770().ptr == Ptr{Cvoid}(UInt(0xfeedface))
+
+bar27770() = Nullable27770().value
+@test_throws UndefRefError bar27770()