commit 2e589aa58a1372909f95e731fd6b8895f6359c3a
author Vladimir Marko <vmarko@google.com> Tue Feb 25 17:53:53 2014 +0000
committer Vladimir Marko <vmarko@google.com> Tue Feb 25 19:03:17 2014 +0000
tree 6337f7e4765a6c6c1ba5d21e9f3f7c4ebe4971ee
parent 661425e1f90d4f4ed44c66f5e74f48b92a3798df

Encode VmapTable entries offset by 2 to reduce size.

We're using special values 0xffff and 0xfffe for an
fp register marker and for method pointer, respectively.
These values were being encoded as 3 bytes each and
this changes their encoding to 1 byte.

Bug: 9437697
Change-Id: Ic1720e898b131a5d3f6ca87d8e1ecdf76fb4160a

runtime/exception_test.cc

diff --git a/runtime/exception_test.cc b/runtime/exception_test.cc
index c7f537a..910a817 100644
--- a/runtime/exception_test.cc
+++ b/runtime/exception_test.cc
@@ -28,6 +28,7 @@
 #include "sirt_ref.h"
 #include "thread.h"
 #include "UniquePtr.h"
+#include "vmap_table.h"
 
 namespace art {
 
@@ -66,7 +67,7 @@
     fake_mapping_data_.PushBackUnsigned(3 - 0);  // offset 3
     fake_mapping_data_.PushBackSigned(3 - 0);    // maps to dex offset 3
 
-    fake_vmap_table_data_.PushBackUnsigned(0);
+    fake_vmap_table_data_.PushBackUnsigned(0 + VmapTable::kEntryAdjustment);
 
     fake_gc_map_.push_back(0);  // 0 bytes to encode references and native pc offsets.
     fake_gc_map_.push_back(0);

runtime/oat.cc

diff --git a/runtime/oat.cc b/runtime/oat.cc
index 81d4540..945cd77 100644
--- a/runtime/oat.cc
+++ b/runtime/oat.cc
@@ -22,7 +22,7 @@
 namespace art {
 
 const uint8_t OatHeader::kOatMagic[] = { 'o', 'a', 't', '\n' };
-const uint8_t OatHeader::kOatVersion[] = { '0', '1', '4', '\0' };
+const uint8_t OatHeader::kOatVersion[] = { '0', '1', '5', '\0' };
 
 OatHeader::OatHeader() {
   memset(this, 0, sizeof(*this));

runtime/vmap_table.h

diff --git a/runtime/vmap_table.h b/runtime/vmap_table.h
index abc50b9..2fbaebe 100644
--- a/runtime/vmap_table.h
+++ b/runtime/vmap_table.h
@@ -25,6 +25,10 @@
 
 class VmapTable {
  public:
+  // For efficient encoding of special values, entries are adjusted by 2.
+  static constexpr uint16_t kEntryAdjustment = 2u;
+  static constexpr uint16_t kAdjustedFpMarker = static_cast<uint16_t>(0xffffu + kEntryAdjustment);
+
   explicit VmapTable(const uint8_t* table) : table_(table) {
   }
 
@@ -33,11 +37,11 @@
     const uint8_t* table = table_;
     size_t size = DecodeUnsignedLeb128(&table);
     CHECK_LT(n, size);
-    uint16_t entry = DecodeUnsignedLeb128(&table);
+    uint16_t adjusted_entry = DecodeUnsignedLeb128(&table);
     for (size_t i = 0; i < n; ++i) {
-      entry = DecodeUnsignedLeb128(&table);
+      adjusted_entry = DecodeUnsignedLeb128(&table);
     }
-    return entry;
+    return adjusted_entry - kEntryAdjustment;
   }
 
   size_t Size() const {
@@ -58,16 +62,17 @@
     bool is_float = (kind == kFloatVReg) || (kind == kDoubleLoVReg) || (kind == kDoubleHiVReg);
     bool in_floats = false;
     const uint8_t* table = table_;
+    uint16_t adjusted_vreg = vreg + kEntryAdjustment;
     size_t end = DecodeUnsignedLeb128(&table);
     for (size_t i = 0; i < end; ++i) {
       // Stop if we find what we are are looking for.
-      uint16_t entry = DecodeUnsignedLeb128(&table);
-      if ((entry == vreg) && (in_floats == is_float)) {
+      uint16_t adjusted_entry = DecodeUnsignedLeb128(&table);
+      if ((adjusted_entry == adjusted_vreg) && (in_floats == is_float)) {
         *vmap_offset = i;
         return true;
       }
       // 0xffff is the marker for LR (return PC on x86), following it are spilled float registers.
-      if (entry == 0xffff) {
+      if (adjusted_entry == kAdjustedFpMarker) {
         in_floats = true;
       }
     }
@@ -89,7 +94,7 @@
     if (UNLIKELY(is_float)) {
       const uint8_t* table = table_;
       DecodeUnsignedLeb128(&table);  // Skip size.
-      while (DecodeUnsignedLeb128(&table) != 0xffff) {
+      while (DecodeUnsignedLeb128(&table) != kAdjustedFpMarker) {
         matches++;
       }
       matches++;