[debugging] print ranges for consecutive values with %DebugPrint

With this CL repeated values in elements are combined into a single printout with a range.

BEFORE:
- elements = {
  0: <undefined>
  1: <undefined>
  2: <the_hole>
}

AFTER:
 - elements = {
       0-1: <undefined>
         2: <the_hole>
}

BUG=

Review-Url: https://codereview.chromium.org/2169143003
Cr-Commit-Position: refs/heads/master@{#38069}

src/objects-printer.cc

@@ -4,6 +4,7 @@
 
 #include "src/objects.h"
 
+#include <iomanip>
 #include <memory>
 
 #include "src/disasm.h"
@@ -317,12 +318,35 @@ void JSObject::PrintProperties(std::ostream& os) {  // NOLINT
   }
 }
 
-
-template <class T>
+template <class T, bool print_the_hole>
 static void DoPrintElements(std::ostream& os, Object* object) {  // NOLINT
-  T* p = T::cast(object);
-  for (int i = 0; i < p->length(); i++) {
-    os << "\n   " << i << ": " << p->get_scalar(i);
+  T* array = T::cast(object);
+  if (array->length() == 0) return;
+  int previous_index = 0;
+  double previous_value = array->get_scalar(0);
+  double value;
+  int i;
+  for (i = 1; i <= array->length(); i++) {
+    if (i < array->length()) value = array->get_scalar(i);
+    bool values_are_nan = std::isnan(previous_value) && std::isnan(value);
+    if ((previous_value == value || values_are_nan) && i != array->length()) {
+      continue;
+    }
+    os << "\n";
+    std::stringstream ss;
+    ss << previous_index;
+    if (previous_index != i - 1) {
+      ss << '-' << (i - 1);
+    }
+    os << std::setw(12) << ss.str() << ": ";
+    if (print_the_hole &&
+        FixedDoubleArray::cast(object)->is_the_hole(previous_index)) {
+      os << "<the_hole>";
+    } else {
+      os << previous_value;
+    }
+    previous_index = i;
+    previous_value = value;
   }
 }
 
@@ -330,6 +354,7 @@ static void DoPrintElements(std::ostream& os, Object* object) {  // NOLINT
 void JSObject::PrintElements(std::ostream& os) {  // NOLINT
   // Don't call GetElementsKind, its validation code can cause the printer to
   // fail when debugging.
+  if (elements()->length() == 0) return;
   switch (map()->elements_kind()) {
     case FAST_HOLEY_SMI_ELEMENTS:
     case FAST_SMI_ELEMENTS:
@@ -337,45 +362,49 @@ void JSObject::PrintElements(std::ostream& os) {  // NOLINT
     case FAST_ELEMENTS:
     case FAST_STRING_WRAPPER_ELEMENTS: {
       // Print in array notation for non-sparse arrays.
-      FixedArray* p = FixedArray::cast(elements());
-      for (int i = 0; i < p->length(); i++) {
-        os << "\n   " << i << ": " << Brief(p->get(i));
+      FixedArray* array = FixedArray::cast(elements());
+      Object* previous_value = array->get(0);
+      Object* value;
+      int previous_index = 0;
+      int i;
+      for (i = 1; i <= array->length(); i++) {
+        if (i < array->length()) value = array->get(i);
+        if (previous_value == value && i != array->length()) {
+          continue;
+        }
+        os << "\n";
+        std::stringstream ss;
+        ss << previous_index;
+        if (previous_index != i - 1) {
+          ss << '-' << (i - 1);
+        }
+        os << std::setw(12) << ss.str() << ": " << Brief(previous_value);
+        previous_index = i;
+        previous_value = value;
       }
       break;
     }
     case FAST_HOLEY_DOUBLE_ELEMENTS:
     case FAST_DOUBLE_ELEMENTS: {
-      // Print in array notation for non-sparse arrays.
-      if (elements()->length() > 0) {
-        FixedDoubleArray* p = FixedDoubleArray::cast(elements());
-        for (int i = 0; i < p->length(); i++) {
-          os << "\n   " << i << ": ";
-          if (p->is_the_hole(i)) {
-            os << "<the hole>";
-          } else {
-            os << p->get_scalar(i);
-          }
-        }
-      }
+      DoPrintElements<FixedDoubleArray, true>(os, elements());
       break;
     }
 
-
-#define PRINT_ELEMENTS(Kind, Type)         \
-  case Kind: {                             \
-    DoPrintElements<Type>(os, elements()); \
-    break;                                 \
+#define PRINT_ELEMENTS(Kind, Type)                \
+  case Kind: {                                    \
+    DoPrintElements<Type, false>(os, elements()); \
+    break;                                        \
   }
 
-    PRINT_ELEMENTS(UINT8_ELEMENTS, FixedUint8Array)
-    PRINT_ELEMENTS(UINT8_CLAMPED_ELEMENTS, FixedUint8ClampedArray)
-    PRINT_ELEMENTS(INT8_ELEMENTS, FixedInt8Array)
-    PRINT_ELEMENTS(UINT16_ELEMENTS, FixedUint16Array)
-    PRINT_ELEMENTS(INT16_ELEMENTS, FixedInt16Array)
-    PRINT_ELEMENTS(UINT32_ELEMENTS, FixedUint32Array)
-    PRINT_ELEMENTS(INT32_ELEMENTS, FixedInt32Array)
-    PRINT_ELEMENTS(FLOAT32_ELEMENTS, FixedFloat32Array)
-    PRINT_ELEMENTS(FLOAT64_ELEMENTS, FixedFloat64Array)
+      PRINT_ELEMENTS(UINT8_ELEMENTS, FixedUint8Array)
+      PRINT_ELEMENTS(UINT8_CLAMPED_ELEMENTS, FixedUint8ClampedArray)
+      PRINT_ELEMENTS(INT8_ELEMENTS, FixedInt8Array)
+      PRINT_ELEMENTS(UINT16_ELEMENTS, FixedUint16Array)
+      PRINT_ELEMENTS(INT16_ELEMENTS, FixedInt16Array)
+      PRINT_ELEMENTS(UINT32_ELEMENTS, FixedUint32Array)
+      PRINT_ELEMENTS(INT32_ELEMENTS, FixedInt32Array)
+      PRINT_ELEMENTS(FLOAT32_ELEMENTS, FixedFloat32Array)
+      PRINT_ELEMENTS(FLOAT64_ELEMENTS, FixedFloat64Array)
 
 #undef PRINT_ELEMENTS