commit 6de8833fb64e59301eada4005ed04da995796170
author David Srbecky <dsrbecky@google.com> Sun Jun 03 12:00:11 2018 +0100
committer David Srbecky <dsrbecky@google.com> Thu Jun 07 12:00:18 2018 +0100
tree 9f5b731ae1c0428cf5dcae4105936a7a165a43c9
parent d97e0828958fd14a962e37af2865bc2e628547ce

Delta-compress register maps in stack maps.

The register maps tend to be similar from stack map to stack map,
so instead of encoding them again, store only the modified ones.

The dex register bitmap stores the delta now - if register has
been modified since the previous stack map, the bit will be set.

The decoding logic scans backwards through stack maps until it
eventfully finds the most recent value of each register.

This CL saves ~2.5% of .oat file size (~10% of stackmap size).

Due to the scan, this makes dex register decoding slower by factor
of 2.5, but that still beats the old algorithm before refactoring.

Test: test-art-host-gtest-stack_map_test
Change-Id: Id5217a329eb757954e0c9447f38b05ec34118f84

compiler/optimizing/stack_map_test.cc

diff --git a/compiler/optimizing/stack_map_test.cc b/compiler/optimizing/stack_map_test.cc
index 77aa3ef..0be276c 100644
--- a/compiler/optimizing/stack_map_test.cc
+++ b/compiler/optimizing/stack_map_test.cc
@@ -358,13 +358,6 @@
     ASSERT_EQ(Kind::kConstant, location1.GetKind());
     ASSERT_EQ(0, location0.GetValue());
     ASSERT_EQ(-2, location1.GetValue());
-
-    // Test that the inline info dex register map deduplicated to the same offset as the stack map
-    // one.
-    ASSERT_TRUE(stack_map.HasInlineInfo());
-    InlineInfo inline_info = code_info.GetInlineInfoAtDepth(stack_map, 0);
-    EXPECT_EQ(inline_info.GetDexRegisterMapIndex(),
-              stack_map.GetDexRegisterMapIndex());
   }
 }
 
@@ -466,13 +459,9 @@
   ASSERT_EQ(2, dex_registers2.GetMachineRegister(0));
   ASSERT_EQ(-2, dex_registers2.GetConstant(1));
 
-  // Verify dex register map offsets.
-  ASSERT_EQ(sm0.GetDexRegisterMapIndex(),
-            sm1.GetDexRegisterMapIndex());
-  ASSERT_NE(sm0.GetDexRegisterMapIndex(),
-            sm2.GetDexRegisterMapIndex());
-  ASSERT_NE(sm1.GetDexRegisterMapIndex(),
-            sm2.GetDexRegisterMapIndex());
+  // Verify dex register mask offsets.
+  ASSERT_FALSE(sm1.HasDexRegisterMaskIndex());  // No delta.
+  ASSERT_TRUE(sm2.HasDexRegisterMaskIndex());  // Has delta.
 }
 
 TEST(StackMapTest, TestNoDexRegisterMap) {
@@ -649,8 +638,6 @@
     ASSERT_EQ(80, dex_registers2.GetStackOffsetInBytes(0));
     ASSERT_EQ(10, dex_registers2.GetConstant(1));
     ASSERT_EQ(5, dex_registers2.GetMachineRegister(2));
-
-    ASSERT_FALSE(if1_2.HasDexRegisterMap());
   }
 
   {
@@ -682,8 +669,6 @@
     ASSERT_EQ(10u, if2_2.GetDexPc());
     ASSERT_TRUE(if2_2.EncodesArtMethod());
 
-    ASSERT_FALSE(if2_0.HasDexRegisterMap());
-
     DexRegisterMap dex_registers1 = ci.GetDexRegisterMapAtDepth(1, sm3, 1);
     ASSERT_EQ(2, dex_registers1.GetMachineRegister(0));