Eliminate redundant array bound checks (checks already performed earlier in the DT).

As a special case, for checks on index expressions with the form (expr + constant) if a smaller constant is checked later in the DT also eliminate the check.
Finally, if a larger constant is checked later in the same BB do the more general check (larger constant) earlier instead of the less general one.
This will not cause useless deoptimizations because, since we are in the same BB, all the checks would have been executed anyway.
BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10032029

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11437 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -195,6 +195,8 @@ DEFINE_bool(trap_on_deopt, false, "put a break point before deoptimizing")
 DEFINE_bool(deoptimize_uncommon_cases, true, "deoptimize uncommon cases")
 DEFINE_bool(polymorphic_inlining, true, "polymorphic inlining")
 DEFINE_bool(use_osr, true, "use on-stack replacement")
+DEFINE_bool(array_bounds_checks_elimination, true,
+            "perform array bounds checks elimination")
 
 DEFINE_bool(trace_osr, false, "trace on-stack replacement")
 DEFINE_int(stress_runs, 0, "number of stress runs")

src/hydrogen-instructions.cc

@@ -416,6 +416,7 @@ void HValue::Kill() {
   SetFlag(kIsDead);
   for (int i = 0; i < OperandCount(); ++i) {
     HValue* operand = OperandAt(i);
+    if (operand == NULL) continue;
     HUseListNode* first = operand->use_list_;
     if (first != NULL && first->value() == this && first->index() == i) {
       operand->use_list_ = first->tail();
@@ -612,6 +613,7 @@ void HInstruction::Verify() {
   HBasicBlock* cur_block = block();
   for (int i = 0; i < OperandCount(); ++i) {
     HValue* other_operand = OperandAt(i);
+    if (other_operand == NULL) continue;
     HBasicBlock* other_block = other_operand->block();
     if (cur_block == other_block) {
       if (!other_operand->IsPhi()) {

src/hydrogen.h

@@ -241,7 +241,7 @@ class HLoopInformation: public ZoneObject {
   HStackCheck* stack_check_;
 };
 
-
+class BoundsCheckTable;
 class HGraph: public ZoneObject {
  public:
   explicit HGraph(CompilationInfo* info);
@@ -266,6 +266,7 @@ class HGraph: public ZoneObject {
   void OrderBlocks();
   void AssignDominators();
   void ReplaceCheckedValues();
+  void EliminateRedundantBoundsChecks();
   void PropagateDeoptimizingMark();
 
   // Returns false if there are phi-uses of the arguments-object
@@ -358,6 +359,7 @@ class HGraph: public ZoneObject {
   void InferTypes(ZoneList<HValue*>* worklist);
   void InitializeInferredTypes(int from_inclusive, int to_inclusive);
   void CheckForBackEdge(HBasicBlock* block, HBasicBlock* successor);
+  void EliminateRedundantBoundsChecks(HBasicBlock* bb, BoundsCheckTable* table);
 
   Isolate* isolate_;
   int next_block_id_;

src/v8-counters.h

@@ -236,6 +236,8 @@ namespace internal {
   SC(math_sin, V8.MathSin)                                            \
   SC(math_sqrt, V8.MathSqrt)                                          \
   SC(math_tan, V8.MathTan)                                            \
+  SC(array_bounds_checks_seen, V8.ArrayBoundsChecksSeen)              \
+  SC(array_bounds_checks_removed, V8.ArrayBoundsChecksRemoved)        \
   SC(transcendental_cache_hit, V8.TranscendentalCacheHit)             \
   SC(transcendental_cache_miss, V8.TranscendentalCacheMiss)           \
   SC(stack_interrupts, V8.StackInterrupts)                            \

test/mjsunit/array-bounds-check-removal.js

+// Copyright 2011 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Flags: --allow-natives-syntax --expose-gc
+
+var a = new Int32Array(1024);
+
+function test_base(base,cond) {
+  a[base + 1] = 1;
+  a[base + 4] = 2;
+  a[base + 3] = 3;
+  a[base + 2] = 4;
+  a[base + 4] = base + 4;
+  if (cond) {
+    a[base + 1] = 1;
+    a[base + 2] = 2;
+    a[base + 2] = 3;
+    a[base + 2] = 4;
+    a[base + 4] = base + 4;
+  } else {
+    a[base + 6] = 1;
+    a[base + 4] = 2;
+    a[base + 3] = 3;
+    a[base + 2] = 4;
+    a[base + 4] = base - 4;
+  }
+}
+
+function check_test_base(base,cond) {
+  if (cond) {
+    assertEquals(1, a[base + 1]);
+    assertEquals(4, a[base + 2]);
+    assertEquals(base + 4, a[base + 4]);
+  } else {
+    assertEquals(1, a[base + 6]);
+    assertEquals(3, a[base + 3]);
+    assertEquals(4, a[base + 2]);
+    assertEquals(base - 4, a[base + 4]);
+  }
+}
+
+
+function test_minus(base,cond) {
+  a[base - 1] = 1;
+  a[base - 2] = 2;
+  a[base + 4] = 3;
+  a[base] = 4;
+  a[base + 4] = base + 4;
+  if (cond) {
+    a[base - 4] = 1;
+    a[base + 5] = 2;
+    a[base + 3] = 3;
+    a[base + 2] = 4;
+    a[base + 4] = base + 4;
+  } else {
+    a[base + 6] = 1;
+    a[base + 4] = 2;
+    a[base + 3] = 3;
+    a[base + 2] = 4;
+    a[base + 4] = base - 4;
+  }
+}
+
+function check_test_minus(base,cond) {
+  if (cond) {
+    assertEquals(2, a[base + 5]);
+    assertEquals(3, a[base + 3]);
+    assertEquals(4, a[base + 2]);
+    assertEquals(base + 4, a[base + 4]);
+  } else {
+    assertEquals(1, a[base + 6]);
+    assertEquals(3, a[base + 3]);
+    assertEquals(4, a[base + 2]);
+    assertEquals(base - 4, a[base + 4]);
+  }
+}
+
+test_base(1,true);
+test_base(2,true);
+test_base(1,false);
+test_base(2,false);
+%OptimizeFunctionOnNextCall(test_base);
+test_base(3,true);
+check_test_base(3,true);
+test_base(3,false);
+check_test_base(3,false);
+
+test_minus(5,true);
+test_minus(6,true);
+%OptimizeFunctionOnNextCall(test_minus);
+test_minus(7,true);
+check_test_minus(7,true);
+test_minus(7,false);
+check_test_minus(7,false);
+
+// Optimization status:
+// YES: 1
+// NO: 2
+// ALWAYS: 3
+// NEVER: 4
+
+if (false) {
+test_base(5,true);
+test_base(6,true);
+test_base(5,false);
+test_base(6,false);
+%OptimizeFunctionOnNextCall(test_base);
+test_base(-2,true);
+assertTrue(%GetOptimizationStatus(test_base) != 1);
+
+test_base(5,true);
+test_base(6,true);
+test_base(5,false);
+test_base(6,false);
+%OptimizeFunctionOnNextCall(test_base);
+test_base(2048,true);
+assertTrue(%GetOptimizationStatus(test_base) != 1);
+}
+
+gc();
+