From 97585ab8b5b7bec0031dc7a8191a3d1f02d27430 Mon Sep 17 00:00:00 2001
From: "alexandre.rames@arm.com"
 <alexandre.rames@arm.com@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Mon, 14 Apr 2014 11:08:14 +0000
Subject: [PATCH] ARM64: Avoid iterating through all unresolved branch infos
 when many are pending.

Instead, inspect the label chain and delete pending information for every branch
in the chain.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/227043010

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20715 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 src/arm64/assembler-arm64.cc   | 47 ++++++++++++++++++++++++++--------
 src/arm64/assembler-arm64.h    |  9 +++++++
 src/arm64/instructions-arm64.h |  4 +++
 3 files changed, 50 insertions(+), 10 deletions(-)

diff --git a/src/arm64/assembler-arm64.cc b/src/arm64/assembler-arm64.cc
index 5695623afd..b399277543 100644
--- a/src/arm64/assembler-arm64.cc
+++ b/src/arm64/assembler-arm64.cc
@@ -545,6 +545,40 @@ int Assembler::LinkAndGetByteOffsetTo(Label* label) {
 }
 
 
+void Assembler::DeleteUnresolvedBranchInfoForLabelTraverse(Label* label) {
+  ASSERT(label->is_linked());
+  CheckLabelLinkChain(label);
+
+  int link_offset = label->pos();
+  int link_pcoffset;
+  bool end_of_chain = false;
+
+  while (!end_of_chain) {
+    Instruction * link = InstructionAt(link_offset);
+    link_pcoffset = link->ImmPCOffset();
+
+    // ADR instructions are not handled by veneers.
+    if (link->IsImmBranch()) {
+      int max_reachable_pc = InstructionOffset(link) +
+          Instruction::ImmBranchRange(link->BranchType());
+      typedef std::multimap<int, FarBranchInfo>::iterator unresolved_info_it;
+      std::pair<unresolved_info_it, unresolved_info_it> range;
+      range = unresolved_branches_.equal_range(max_reachable_pc);
+      unresolved_info_it it;
+      for (it = range.first; it != range.second; ++it) {
+        if (it->second.pc_offset_ == link_offset) {
+          unresolved_branches_.erase(it);
+          break;
+        }
+      }
+    }
+
+    end_of_chain = (link_pcoffset == 0);
+    link_offset = link_offset + link_pcoffset;
+  }
+}
+
+
 void Assembler::DeleteUnresolvedBranchInfoForLabel(Label* label) {
   if (unresolved_branches_.empty()) {
     ASSERT(next_veneer_pool_check_ == kMaxInt);
@@ -552,16 +586,9 @@ void Assembler::DeleteUnresolvedBranchInfoForLabel(Label* label) {
   }
 
   if (label->is_linked()) {
-    // Branches to this label will be resolved when the label is bound below.
-    std::multimap<int, FarBranchInfo>::iterator it_tmp, it;
-    it = unresolved_branches_.begin();
-    while (it != unresolved_branches_.end()) {
-      it_tmp = it++;
-      if (it_tmp->second.label_ == label) {
-        CHECK(it_tmp->first >= pc_offset());
-        unresolved_branches_.erase(it_tmp);
-      }
-    }
+    // Branches to this label will be resolved when the label is bound, normally
+    // just after all the associated info has been deleted.
+    DeleteUnresolvedBranchInfoForLabelTraverse(label);
   }
   if (unresolved_branches_.empty()) {
     next_veneer_pool_check_ = kMaxInt;
diff --git a/src/arm64/assembler-arm64.h b/src/arm64/assembler-arm64.h
index 391a900763..794f87c01e 100644
--- a/src/arm64/assembler-arm64.h
+++ b/src/arm64/assembler-arm64.h
@@ -1694,6 +1694,10 @@ class Assembler : public AssemblerBase {
     return reinterpret_cast<Instruction*>(buffer_ + offset);
   }
 
+  ptrdiff_t InstructionOffset(Instruction* instr) const {
+    return reinterpret_cast<byte*>(instr) - buffer_;
+  }
+
   // Register encoding.
   static Instr Rd(CPURegister rd) {
     ASSERT(rd.code() != kSPRegInternalCode);
@@ -2183,6 +2187,11 @@ class Assembler : public AssemblerBase {
   // not later attempt (likely unsuccessfully) to patch it to branch directly to
   // the label.
   void DeleteUnresolvedBranchInfoForLabel(Label* label);
+  // This function deletes the information related to the label by traversing
+  // the label chain, and for each PC-relative instruction in the chain checking
+  // if pending unresolved information exists. Its complexity is proportional to
+  // the length of the label chain.
+  void DeleteUnresolvedBranchInfoForLabelTraverse(Label* label);
 
  private:
   PositionsRecorder positions_recorder_;
diff --git a/src/arm64/instructions-arm64.h b/src/arm64/instructions-arm64.h
index de76b69b6b..cfa63a345c 100644
--- a/src/arm64/instructions-arm64.h
+++ b/src/arm64/instructions-arm64.h
@@ -192,6 +192,10 @@ class Instruction {
     return Mask(TestBranchFMask) == TestBranchFixed;
   }
 
+  bool IsImmBranch() const {
+    return BranchType() != UnknownBranchType;
+  }
+
   bool IsLdrLiteral() const {
     return Mask(LoadLiteralFMask) == LoadLiteralFixed;
   }