From 8f6b99fba2d043265a84d599a967d52f66738ad6 Mon Sep 17 00:00:00 2001
From: Nicolas Geoffray <ngeoffray@google.com>
Date: Tue, 28 Sep 2021 17:51:17 +0000
Subject: Revert "ART: Removes SuspendCheck for plain loops with a low trip
 count."

This reverts commit 3de02fb67de386368c9fe39ab5a0133afcf1d785.

Reason for revert: b/201413752

Change-Id: I8a3a56cfb81fa88f49992615696260dfbc79bb67
---
 compiler/optimizing/loop_optimization.cc | 55 +++-----------------------------
 1 file changed, 4 insertions(+), 51 deletions(-)

(limited to 'compiler/optimizing/loop_optimization.cc')

diff --git a/compiler/optimizing/loop_optimization.cc b/compiler/optimizing/loop_optimization.cc
index cd054822cd..02ee4ec057 100644
--- a/compiler/optimizing/loop_optimization.cc
+++ b/compiler/optimizing/loop_optimization.cc
@@ -635,47 +635,6 @@ bool HLoopOptimization::TraverseLoopsInnerToOuter(LoopNode* node) {
   return changed;
 }
 
-//
-// This optimization applies to loops with plain simple operations
-// (I.e. no calls to java code or runtime) with a known small trip_count * instr_count
-// value.
-//
-bool HLoopOptimization::TryToRemoveSuspendCheckFromLoopHeader(LoopAnalysisInfo* analysis_info,
-                                                              bool generate_code) {
-  if (!graph_->SuspendChecksAreAllowedToBeRemoved()) {
-    return false;
-  }
-
-  int64_t trip_count = analysis_info->GetTripCount();
-
-  if (trip_count == LoopAnalysisInfo::kUnknownTripCount) {
-    return false;
-  }
-
-  int64_t instruction_count = analysis_info->GetNumberOfInstructions();
-  int64_t total_instruction_count = trip_count * instruction_count;
-
-  // The inclusion of the HasInstructionsPreventingScalarOpts() prevents this
-  // optimization from being applied to loops that have calls.
-  bool can_optimize =
-      total_instruction_count <= HLoopOptimization::kMaxTotalInstRemoveSuspendCheck &&
-      !analysis_info->HasInstructionsPreventingScalarOpts();
-
-  if (!can_optimize) {
-    return false;
-  }
-
-  if (generate_code) {
-    HLoopInformation* loop_info = analysis_info->GetLoopInfo();
-    HBasicBlock* header = loop_info->GetHeader();
-    HInstruction* instruction = header->GetLoopInformation()->GetSuspendCheck();
-    header->RemoveInstruction(instruction);
-    loop_info->SetSuspendCheck(nullptr);
-  }
-
-  return true;
-}
-
 //
 // Optimization.
 //
@@ -820,7 +779,7 @@ bool HLoopOptimization::TryOptimizeInnerLoopFinite(LoopNode* node) {
 }
 
 bool HLoopOptimization::OptimizeInnerLoop(LoopNode* node) {
-  return TryOptimizeInnerLoopFinite(node) || TryLoopScalarOpts(node);
+  return TryOptimizeInnerLoopFinite(node) || TryPeelingAndUnrolling(node);
 }
 
 
@@ -926,7 +885,7 @@ bool HLoopOptimization::TryFullUnrolling(LoopAnalysisInfo* analysis_info, bool g
   return true;
 }
 
-bool HLoopOptimization::TryLoopScalarOpts(LoopNode* node) {
+bool HLoopOptimization::TryPeelingAndUnrolling(LoopNode* node) {
   HLoopInformation* loop_info = node->loop_info;
   int64_t trip_count = LoopAnalysis::GetLoopTripCount(loop_info, &induction_range_);
   LoopAnalysisInfo analysis_info(loop_info);
@@ -939,16 +898,10 @@ bool HLoopOptimization::TryLoopScalarOpts(LoopNode* node) {
 
   if (!TryFullUnrolling(&analysis_info, /*generate_code*/ false) &&
       !TryPeelingForLoopInvariantExitsElimination(&analysis_info, /*generate_code*/ false) &&
-      !TryUnrollingForBranchPenaltyReduction(&analysis_info, /*generate_code*/ false) &&
-      !TryToRemoveSuspendCheckFromLoopHeader(&analysis_info, /*generate_code*/ false)) {
+      !TryUnrollingForBranchPenaltyReduction(&analysis_info, /*generate_code*/ false)) {
     return false;
   }
 
-  // Try the suspend check removal even for non-clonable loops. Also this
-  // optimization doesn't interfere with other scalar loop optimizations so it can
-  // be done prior to them.
-  bool removed_suspend_check = TryToRemoveSuspendCheckFromLoopHeader(&analysis_info);
-
   // Run 'IsLoopClonable' the last as it might be time-consuming.
   if (!LoopClonerHelper::IsLoopClonable(loop_info)) {
     return false;
@@ -956,7 +909,7 @@ bool HLoopOptimization::TryLoopScalarOpts(LoopNode* node) {
 
   return TryFullUnrolling(&analysis_info) ||
          TryPeelingForLoopInvariantExitsElimination(&analysis_info) ||
-         TryUnrollingForBranchPenaltyReduction(&analysis_info) || removed_suspend_check;
+         TryUnrollingForBranchPenaltyReduction(&analysis_info);
 }
 
 //
-- 
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