handle zero case in enum comparison (#484)

decompiler/IR2/FormExpressionAnalysis.cpp

@@ -2371,6 +2371,40 @@ Matcher make_int_uint_cast_matcher(const Matcher& thing) {
 // ConditionElement
 ///////////////////
 
+namespace {
+/*!
+ * Try to make a pretty looking constant out of value for comparing to something of type.
+ * If we can't do anything nice, return nullptr.
+ */
+Form* try_make_constant_for_compare(Form* value,
+                                    const TypeSpec& type,
+                                    FormPool& pool,
+                                    const Env& env) {
+  if (get_goal_integer_constant(value, env) && env.dts->ts.try_enum_lookup(type)) {
+    return cast_form(value, type, pool, env);
+  }
+  return nullptr;
+}
+
+Form* try_make_constant_from_int_for_compare(s64 value,
+                                             const TypeSpec& type,
+                                             FormPool& pool,
+                                             const Env& env) {
+  auto enum_type_info = env.dts->ts.try_enum_lookup(type);
+  if (enum_type_info) {
+    if (enum_type_info->is_bitfield()) {
+      if (value != 0) {
+        // prefer (zero? x) for bitfield enums.
+        return cast_to_bitfield_enum(enum_type_info, pool, env, value);
+      }
+    } else {
+      return cast_to_int_enum(enum_type_info, pool, env, value);
+    }
+  }
+  return nullptr;
+}
+}  // namespace
+
 FormElement* ConditionElement::make_zero_check_generic(const Env& env,
                                                        FormPool& pool,
                                                        const std::vector<Form*>& source_forms,
@@ -2405,6 +2439,13 @@ FormElement* ConditionElement::make_zero_check_generic(const Env& env,
     }
   }
 
+  auto nice_constant = try_make_constant_from_int_for_compare(0, source_types.at(0), pool, env);
+  if (nice_constant) {
+    return pool.alloc_element<GenericElement>(
+        GenericOperator::make_fixed(FixedOperatorKind::EQ),
+        std::vector<Form*>{source_forms.at(0), nice_constant});
+  }
+
   return pool.alloc_element<GenericElement>(GenericOperator::make_compare(m_kind), source_forms);
 }
 
@@ -2442,12 +2483,11 @@ FormElement* ConditionElement::make_equal_check_generic(const Env& env,
     return pool.alloc_element<GenericElement>(GenericOperator::make_fixed(FixedOperatorKind::NULLP),
                                               source_forms.at(0));
   } else {
-    auto int_val = get_goal_integer_constant(source_forms.at(1), env);
-    auto src0_as_enum = env.dts->ts.try_enum_lookup(source_types.at(0));
-    if (src0_as_enum && int_val) {
-      // if comparing an enum against a constant integer, rewrite the enum.
+    auto nice_constant =
+        try_make_constant_for_compare(source_forms.at(1), source_types.at(0), pool, env);
+    if (nice_constant) {
       auto forms_with_cast = source_forms;
-      forms_with_cast.at(1) = cast_form(source_forms.at(1), source_types.at(0), pool, env);
+      forms_with_cast.at(1) = nice_constant;
       return pool.alloc_element<GenericElement>(GenericOperator::make_fixed(FixedOperatorKind::EQ),
                                                 forms_with_cast);
     } else {

decompiler/IR2/bitfields.cpp

@@ -563,15 +563,7 @@ Form* cast_to_bitfield_enum(const EnumType* type_info,
   assert(type_info->is_bitfield());
   auto integer = get_goal_integer_constant(strip_int_or_uint_cast(in), env);
   if (integer) {
-    auto elts =
-        decompile_bitfield_enum_from_int(TypeSpec(type_info->get_name()), env.dts->ts, *integer);
-    auto oper = GenericOperator::make_function(
-        pool.alloc_single_element_form<ConstantTokenElement>(nullptr, type_info->get_name()));
-    std::vector<Form*> form_elts;
-    for (auto& x : elts) {
-      form_elts.push_back(pool.alloc_single_element_form<ConstantTokenElement>(nullptr, x));
-    }
-    return pool.alloc_single_element_form<GenericElement>(nullptr, oper, form_elts);
+    return cast_to_bitfield_enum(type_info, pool, env, *integer);
   } else {
     // all failed, just return whatever.
     return pool.alloc_single_element_form<CastElement>(nullptr, typespec, in);
@@ -594,6 +586,7 @@ Form* cast_to_int_enum(const EnumType* type_info,
 }
 
 Form* cast_to_int_enum(const EnumType* type_info, FormPool& pool, const Env& env, s64 in) {
+  assert(!type_info->is_bitfield());
   auto entry = decompile_int_enum_from_int(TypeSpec(type_info->get_name()), env.dts->ts, in);
   auto oper = GenericOperator::make_function(
       pool.alloc_single_element_form<ConstantTokenElement>(nullptr, type_info->get_name()));
@@ -601,4 +594,16 @@ Form* cast_to_int_enum(const EnumType* type_info, FormPool& pool, const Env& env
       nullptr, oper, pool.alloc_single_element_form<ConstantTokenElement>(nullptr, entry));
 }
 
+Form* cast_to_bitfield_enum(const EnumType* type_info, FormPool& pool, const Env& env, s64 in) {
+  assert(type_info->is_bitfield());
+  auto elts = decompile_bitfield_enum_from_int(TypeSpec(type_info->get_name()), env.dts->ts, in);
+  auto oper = GenericOperator::make_function(
+      pool.alloc_single_element_form<ConstantTokenElement>(nullptr, type_info->get_name()));
+  std::vector<Form*> form_elts;
+  for (auto& x : elts) {
+    form_elts.push_back(pool.alloc_single_element_form<ConstantTokenElement>(nullptr, x));
+  }
+  return pool.alloc_single_element_form<GenericElement>(nullptr, oper, form_elts);
+}
+
 }  // namespace decompiler

decompiler/IR2/bitfields.h

@@ -178,6 +178,7 @@ Form* cast_to_int_enum(const EnumType* type_info,
                        Form* in);
 
 Form* cast_to_int_enum(const EnumType* type_info, FormPool& pool, const Env& env, s64 in);
+Form* cast_to_bitfield_enum(const EnumType* type_info, FormPool& pool, const Env& env, s64 in);
 
 std::optional<u64> get_goal_integer_constant(Form* in, const Env&);
 

test/decompiler/reference/engine/dma/dma-disasm_REF.gc

@@ -613,7 +613,7 @@
                     ((= v1-1 (dma-tag-id cnt))
                      "cnt"
                      )
-                    ((zero? v1-1)
+                    ((= v1-1 (dma-tag-id refe))
                      "refe"
                      )
                     (else
@@ -754,7 +754,7 @@
            data-2
            (the-as dma-packet (&-> (the-as (pointer uint64) data-2) 2))
            )
-          (if (zero? (-> current-tag id))
+          (if (= (-> current-tag id) (dma-tag-id refe))
            (set! end-condition #t)
            )
           )

test/decompiler/reference/engine/gfx/hw/gs_REF.gc

@@ -115,7 +115,7 @@
     ((= v1-0 (gs-psm ct24))
      "ct24"
      )
-    ((zero? v1-0)
+    ((= v1-0 (gs-psm ct32))
      "ct32"
      )
     (else

test/decompiler/reference/engine/load/file-io_REF.gc

@@ -105,7 +105,7 @@
    ((= kind (file-kind tpage))
     (format *file-temp-string* "texture-page~D/tpage-~S" 7 name)
     )
-   ((zero? kind)
+   ((= kind (file-kind level-bt))
     (format *file-temp-string* "level~D/~S-bt" 30 name)
     )
    ((= kind (file-kind tx))
@@ -138,7 +138,7 @@
 (defun make-vfile-name ((kind file-kind) (name string))
   (clear *file-temp-string*)
   (cond
-   ((zero? kind)
+   ((= kind (file-kind level-bt))
     (format *file-temp-string* "$LEVEL/~S" name)
     )
    ((= kind (file-kind art-group))
@@ -163,7 +163,7 @@
                                  )
                                 7
                                 )
-                               ((zero? v1-0)
+                               ((= v1-0 (file-kind level-bt))
                                 30
                                 )
                                ((= v1-0 (file-kind art-group))
@@ -182,7 +182,7 @@
                      ((= v1-1 (file-kind tpage))
                       "texture-page"
                       )
-                     ((zero? v1-1)
+                     ((= v1-1 (file-kind level-bt))
                       "bsp-header"
                       )
                      ((= v1-1 (file-kind art-group))