codegen: implement isdefined_tfunc check more similarly to inference (#52069)

Author: vtjnash

src/cgutils.cpp

@@ -2491,14 +2491,40 @@ static jl_cgval_t emit_getfield_knownidx(jl_codectx_t &ctx, const jl_cgval_t &st
                                          unsigned idx, jl_datatype_t *jt,
                                          enum jl_memory_order order, Value **nullcheck=nullptr);
 
+static bool field_may_be_null(const jl_cgval_t &strct, jl_datatype_t *stt, size_t idx)
+{
+    size_t nfields = jl_datatype_nfields(stt);
+    if (idx < nfields - (unsigned)stt->name->n_uninitialized)
+        return false;
+    if (!jl_field_isptr(stt, idx) && !jl_type_hasptr(jl_field_type(stt, idx)))
+        return false;
+    if (strct.constant) {
+        if ((jl_is_immutable(stt) || jl_field_isconst(stt, idx)) && jl_field_isdefined(strct.constant, idx))
+            return false;
+    }
+    return true;
+}
+
+static bool field_may_be_null(const jl_cgval_t &strct, jl_datatype_t *stt)
+{
+    size_t nfields = jl_datatype_nfields(stt);
+    for (size_t i = 0; i < (unsigned)stt->name->n_uninitialized; i++) {
+        size_t idx = nfields - i - 1;
+        if (field_may_be_null(strct, stt, idx))
+            return true;
+    }
+    return false;
+}
+
+
 static bool emit_getfield_unknownidx(jl_codectx_t &ctx,
         jl_cgval_t *ret, jl_cgval_t strct,
         Value *idx, jl_datatype_t *stt, jl_value_t *inbounds,
         enum jl_memory_order order)
 {
     ++EmittedGetfieldUnknowns;
     size_t nfields = jl_datatype_nfields(stt);
-    bool maybe_null = (unsigned)stt->name->n_uninitialized != 0;
+    bool maybe_null = field_may_be_null(strct, stt);
     auto idx0 = [&]() {
         return emit_bounds_check(ctx, strct, (jl_value_t*)stt, idx, ConstantInt::get(ctx.types().T_size, nfields), inbounds);
     };
@@ -2817,8 +2843,7 @@ static jl_cgval_t emit_getfield_knownidx(jl_codectx_t &ctx, const jl_cgval_t &st
         assert(strct.isboxed);
         needlock = boxed(ctx, strct);
     }
-    size_t nfields = jl_datatype_nfields(jt);
-    bool maybe_null = idx >= nfields - (unsigned)jt->name->n_uninitialized;
+    bool maybe_null = field_may_be_null(strct, jt, idx);
     size_t byte_offset = jl_field_offset(jt, idx);
     if (strct.ispointer()) {
         auto tbaa = best_field_tbaa(ctx, strct, jt, idx, byte_offset);
@@ -3873,8 +3898,7 @@ static jl_cgval_t emit_setfield(jl_codectx_t &ctx,
             modifyop, fname);
     }
     unsigned align = jl_field_align(sty, idx0);
-    size_t nfields = jl_datatype_nfields(sty);
-    bool maybe_null = idx0 >= nfields - (unsigned)sty->name->n_uninitialized;
+    bool maybe_null = field_may_be_null(strct, sty, idx0);
     return typed_store(ctx, addr, rhs, cmp, jfty, tbaa, nullptr,
         wb ? boxed(ctx, strct) : nullptr,
         isboxed, Order, FailOrder, align,

src/codegen.cpp

@@ -4843,7 +4843,7 @@ static bool emit_builtin_call(jl_codectx_t &ctx, jl_cgval_t *ret, jl_value_t *f,
             *ret = jl_cgval_t(); // unreachable
             return true;
         }
-        else if (fieldidx < nf - stt->name->n_uninitialized) {
+        else if (!field_may_be_null(obj, stt, fieldidx)) {
             *ret = mark_julia_const(ctx, jl_true);
         }
         else if (jl_field_isptr(stt, fieldidx) || jl_type_hasptr(jl_field_type(stt, fieldidx))) {