Give a length field to stack bitmaps.

runtime/vm/bitmap_test.cc

Index: runtime/vm/bitmap_test.cc
diff --git a/runtime/vm/bitmap_test.cc b/runtime/vm/bitmap_test.cc
index 4e9fc7cdc1c317a172d6126857fe7e4d4cd289a8..d4a39798f7a5260929aaf57a4151a92281755bf1 100644
--- a/runtime/vm/bitmap_test.cc
+++ b/runtime/vm/bitmap_test.cc
@@ -12,15 +12,14 @@ namespace dart {
 TEST_CASE(BitmapBuilder) {
   // Test basic bit map builder operations.
   BitmapBuilder* builder1 = new BitmapBuilder();
-
-  EXPECT_EQ(-1, builder1->Maximum());
-  EXPECT_EQ(-1, builder1->Minimum());
+  EXPECT_EQ(0, builder1->Length());
 
   bool value = true;
   for (int32_t i = 0; i < 128; i++) {
     builder1->Set(i, value);
     value = !value;
   }
+  EXPECT_EQ(128, builder1->Length());
   value = true;
   for (int32_t i = 0; i < 128; i++) {
     EXPECT_EQ(value, builder1->Get(i));
@@ -31,28 +30,29 @@ TEST_CASE(BitmapBuilder) {
     builder1->Set(i, value);
     value = !value;
   }
+  EXPECT_EQ(1024, builder1->Length());
   value = true;
   for (int32_t i = 0; i < 1024; i++) {
     EXPECT_EQ(value, builder1->Get(i));
     value = !value;
   }
   // Create a Stackmap object from the builder and verify its contents.
-  const Stackmap& stackmap1 =
-      Stackmap::Handle(Stackmap::New(0, 1024, builder1));
-  EXPECT_EQ(1022, builder1->Maximum());
-  EXPECT_EQ(0, builder1->Minimum());
+  const Stackmap& stackmap1 = Stackmap::Handle(Stackmap::New(0, builder1));
+  EXPECT_EQ(1024, stackmap1.Length());
   OS::Print("%s\n", stackmap1.ToCString());
   value = true;
   for (int32_t i = 0; i < 1024; i++) {
     EXPECT_EQ(value, stackmap1.IsObject(i));
     value = !value;
   }
-  EXPECT(!stackmap1.IsObject(2056));  // Out of range so returns false.
 
   // Test the SetRange function in the builder.
   builder1->SetRange(0, 256, false);
+  EXPECT_EQ(1024, builder1->Length());
   builder1->SetRange(257, 1024, true);
+  EXPECT_EQ(1025, builder1->Length());
   builder1->SetRange(1025, 2048, false);
+  EXPECT_EQ(2049, builder1->Length());
   for (int32_t i = 0; i <= 256; i++) {
     EXPECT(!builder1->Get(i));
   }
@@ -62,10 +62,8 @@ TEST_CASE(BitmapBuilder) {
   for (int32_t i = 1025; i <= 2048; i++) {
     EXPECT(!builder1->Get(i));
   }
-  const Stackmap& stackmap2 =
-      Stackmap::Handle(Stackmap::New(0, 2049, builder1));
-  EXPECT_EQ(1024, builder1->Maximum());
-  EXPECT_EQ(257, builder1->Minimum());
+  const Stackmap& stackmap2 = Stackmap::Handle(Stackmap::New(0, builder1));
+  EXPECT_EQ(2049, stackmap2.Length());
   for (int32_t i = 0; i <= 256; i++) {
     EXPECT(!stackmap2.IsObject(i));
   }
@@ -75,6 +73,32 @@ TEST_CASE(BitmapBuilder) {
   for (int32_t i = 1025; i <= 2048; i++) {
     EXPECT(!stackmap2.IsObject(i));
   }
+
+  // Test using SetLength to shorten the builder, followed by lengthening.
+  builder1->SetLength(747);
+  EXPECT_EQ(747, builder1->Length());
+  for (int32_t i = 257; i < 747; ++i) {
+    EXPECT(builder1->Get(i));
+  }
+
+  builder1->Set(800, false);
+  EXPECT_EQ(801, builder1->Length());
+  for (int32_t i = 257; i < 747; ++i) {
+    EXPECT(builder1->Get(i));
+  }
+  for (int32_t i = 747; i < 801; ++i) {
+    EXPECT(!builder1->Get(i));
+  }
+
+  builder1->Set(900, true);
+  EXPECT_EQ(901, builder1->Length());
+  for (int32_t i = 257; i < 747; ++i) {
+    EXPECT(builder1->Get(i));
+  }
+  for (int32_t i = 747; i < 900; ++i) {
+    EXPECT(!builder1->Get(i));
+  }
+  EXPECT(builder1->Get(900));
 }
 
 }  // namespace dart