[vm/compiler] Changes in Cid range computation

Rationale:
An incorrect edit slipped into the JIT version, which
had some performance regression. Also we now make
the null optional when not excluded explicitly, since
this results in no ranges for a few cases.

flutter/flutter#28260

Change-Id: I799683d938287661321033d6839fcf2f471b2bc4
Reviewed-on: https://dart-review.googlesource.com/c/94349
Commit-Queue: Aart Bik <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>
Reviewed-by: Alexander Markov <[email protected]>

Author: aartbik

runtime/vm/compiler/backend/il.cc

@@ -131,12 +131,11 @@ const CidRangeVector& HierarchyInfo::SubtypeRangesForClass(
   CidRangeVector& ranges = (*cid_ranges)[klass.id()];
   if (ranges.length() == 0) {
     if (!FLAG_precompiled_mode) {
-      BuildRangesForJIT(table, &ranges, klass,
-                        /*use_subtype_test=*/true,
-                        /*include_abstract*/ false);
+      BuildRangesForJIT(table, &ranges, klass, /*use_subtype_test=*/true,
+                        include_abstract, exclude_null);
     } else {
-      BuildRangesFor(table, &ranges, klass,
-                     /*use_subtype_test=*/true, include_abstract, exclude_null);
+      BuildRangesFor(table, &ranges, klass, /*use_subtype_test=*/true,
+                     include_abstract, exclude_null);
     }
   }
   return ranges;
@@ -155,7 +154,8 @@ const CidRangeVector& HierarchyInfo::SubclassRangesForClass(
     if (!FLAG_precompiled_mode) {
       BuildRangesForJIT(table, &ranges, klass,
                         /*use_subtype_test=*/true,
-                        /*include_abstract=*/false);
+                        /*include_abstract=*/false,
+                        /*exclude_null=*/false);
     } else {
       BuildRangesFor(table, &ranges, klass,
                      /*use_subtype_test=*/false,
@@ -201,6 +201,7 @@ void HierarchyInfo::BuildRangesFor(ClassTable* table,
     if (cid == kTypeArgumentsCid) continue;
     if (cid == kVoidCid) continue;
     if (cid == kDynamicCid) continue;
+    if (cid == kNullCid && !exclude_null) continue;
     cls = table->At(cid);
     if (!include_abstract && cls.is_abstract()) continue;
     if (cls.is_patch()) continue;
@@ -209,7 +210,8 @@ void HierarchyInfo::BuildRangesFor(ClassTable* table,
     // We are either interested in [CidRange]es of subclasses or subtypes.
     bool test_succeeded = false;
     if (cid == kNullCid) {
-      test_succeeded = !exclude_null;
+      ASSERT(exclude_null);
+      test_succeeded = false;
     } else if (use_subtype_test) {
       cls_type = cls.RareType();
       test_succeeded = cls_type.IsSubtypeOf(dst_type, Heap::kNew);
@@ -256,12 +258,14 @@ void HierarchyInfo::BuildRangesForJIT(ClassTable* table,
                                       CidRangeVector* ranges,
                                       const Class& dst_klass,
                                       bool use_subtype_test,
-                                      bool include_abstract) {
+                                      bool include_abstract,
+                                      bool exclude_null) {
   if (dst_klass.InVMHeap()) {
     BuildRangesFor(table, ranges, dst_klass, use_subtype_test, include_abstract,
-                   /*exclude_null=*/false);
+                   exclude_null);
     return;
   }
+  ASSERT(!exclude_null);
 
   Zone* zone = thread()->zone();
   GrowableArray<intptr_t> cids;

runtime/vm/compiler/backend/il.h

@@ -242,7 +242,10 @@ class HierarchyInfo : public ThreadStackResource {
 
  private:
   // Does not use any hierarchy information available in the system but computes
-  // it via O(n) class table traversal.
+  // it via O(n) class table traversal. The boolean parameters denote:
+  //   use_subtype_test : if set, IsSubtypeOf() is used to compute inclusion
+  //   include_abstract : if set, include abstract types (don't care otherwise)
+  //   exclude_null     : if set, exclude null types (don't care otherwise)
   void BuildRangesFor(ClassTable* table,
                       CidRangeVector* ranges,
                       const Class& klass,
@@ -256,7 +259,8 @@ class HierarchyInfo : public ThreadStackResource {
                          CidRangeVector* ranges,
                          const Class& klass,
                          bool use_subtype_test,
-                         bool include_abstract);
+                         bool include_abstract,
+                         bool exclude_null);
 
   CidRangeVector* cid_subtype_ranges_nullable_;
   CidRangeVector* cid_subtype_ranges_abstract_nullable_;