fix JuliaLang#40855, alignment calculation in julia_const_to_llvm (J…

…uliaLang#40864)

This appears as a regression due to doing more constant folding in 1.6+

src/intrinsics.cpp

@@ -202,8 +202,9 @@ static Constant *julia_const_to_llvm(jl_codectx_t &ctx, const void *ptr, jl_data
  const uint8_t *ov = (const uint8_t*)ptr + offs;
  if (jl_is_uniontype(ft)) {
  // compute the same type layout as julia_struct_to_llvm
- size_t fsz = jl_field_size(bt, i);
- size_t al = jl_field_align(bt, i);
+ size_t fsz = 0, al = 0;
+ (void)jl_islayout_inline(ft, &fsz, &al);
+ fsz = jl_field_size(bt, i);
  uint8_t sel = ((const uint8_t*)ptr)[offs + fsz - 1];
  jl_value_t *active_ty = jl_nth_union_component(ft, sel);
  size_t active_sz = jl_datatype_size(active_ty);

test/compiler/codegen.jl

@@ -561,3 +561,12 @@ function f32843(vals0, v)
  vals
 end
 @test_throws UndefVarError f32843([6], Vector[[1]])
+
+# issue #40855, struct constants with union fields
+@enum T40855 X40855
+struct A40855
+ d::Union{Nothing, T40855}
+ b::Union{Nothing, Int}
+end
+g() = string(A40855(X40855, 1))
+@test g() == "$(@__MODULE__).A40855($(@__MODULE__).X40855, 1)"