From 9b1583e7d799a3bb3c0036abb8a0b9fcbfad360a Mon Sep 17 00:00:00 2001
From: Nicolas Geoffray <ngeoffray@google.com>
Date: Tue, 13 Dec 2016 13:43:31 +0000
Subject: [PATCH] Support GVN for HLoadClass::LoadKind::kJitTableAddress.

Fixes performance regressions seen in eg Dhrystone.

Also add comment on why a class may not be found when sharpening.

Test: manual Dhrystone run, performance recovers
Test: ART_TEST_JIT=true test-art-host-run-test-jit
Change-Id: I8e879f1c390f83e8bc930f343beb7b4a41c2f190
---
 compiler/optimizing/nodes.cc      | 29 +++++++++++++++++++----------
 compiler/optimizing/sharpening.cc |  4 +++-
 2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 925d4f1fd..1e946d67b 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -2440,6 +2440,17 @@ std::ostream& operator<<(std::ostream& os, HInvokeStaticOrDirect::ClinitCheckReq
   }
 }
 
+// Helper for InstructionDataEquals to fetch the mirror Class out
+// from a kJitTableAddress LoadClass kind.
+// NO_THREAD_SAFETY_ANALYSIS because even though we're accessing
+// mirrors, they are stored in a variable size handle scope which is always
+// visited during a pause. Also, the only caller of this helper
+// only uses the mirror for pointer comparison.
+static inline mirror::Class* AsMirrorInternal(uint64_t address)
+    NO_THREAD_SAFETY_ANALYSIS {
+  return reinterpret_cast<StackReference<mirror::Class>*>(address)->AsMirrorPtr();
+}
+
 bool HLoadClass::InstructionDataEquals(const HInstruction* other) const {
   const HLoadClass* other_load_class = other->AsLoadClass();
   // TODO: To allow GVN for HLoadClass from different dex files, we should compare the type
@@ -2448,16 +2459,14 @@ bool HLoadClass::InstructionDataEquals(const HInstruction* other) const {
       GetPackedFields() != other_load_class->GetPackedFields()) {
     return false;
   }
-  LoadKind load_kind = GetLoadKind();
-  if (HasAddress(load_kind)) {
-    return GetAddress() == other_load_class->GetAddress();
-  } else if (HasTypeReference(load_kind)) {
-    return IsSameDexFile(GetDexFile(), other_load_class->GetDexFile());
-  } else {
-    DCHECK(HasDexCacheReference(load_kind)) << load_kind;
-    // If the type indexes and dex files are the same, dex cache element offsets
-    // must also be the same, so we don't need to compare them.
-    return IsSameDexFile(GetDexFile(), other_load_class->GetDexFile());
+  switch (GetLoadKind()) {
+    case LoadKind::kBootImageAddress:
+      return GetAddress() == other_load_class->GetAddress();
+    case LoadKind::kJitTableAddress:
+      return AsMirrorInternal(GetAddress()) == AsMirrorInternal(other_load_class->GetAddress());
+    default:
+      DCHECK(HasTypeReference(GetLoadKind()) || HasDexCacheReference(GetLoadKind()));
+      return IsSameDexFile(GetDexFile(), other_load_class->GetDexFile());
   }
 }
 
diff --git a/compiler/optimizing/sharpening.cc b/compiler/optimizing/sharpening.cc
index bbbb1a18c..91efb8001 100644
--- a/compiler/optimizing/sharpening.cc
+++ b/compiler/optimizing/sharpening.cc
@@ -197,7 +197,9 @@ void HSharpening::ProcessLoadClass(HLoadClass* load_class) {
           // out which class loader to use.
           address = reinterpret_cast<uint64_t>(handles_->NewHandle(klass).GetReference());
         } else {
-          // Class not loaded yet. Fallback to the dex cache.
+          // Class not loaded yet. This happens when the dex code requesting
+          // this `HLoadClass` hasn't been executed in the interpreter.
+          // Fallback to the dex cache.
           // TODO(ngeoffray): Generate HDeoptimize instead.
           desired_load_kind = HLoadClass::LoadKind::kDexCacheViaMethod;
         }
-- 
2.11.0