ARM: Use the shifter operand to merge in previous shift instructions.

src/arm/lithium-arm.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/lithium-allocator-inl.h"
 #include "src/arm/lithium-arm.h"
 #include "src/arm/lithium-codegen-arm.h"
 #include "src/hydrogen-osr.h"
@@ skipping 658 matching lines @@
   UNREACHABLE();
   return NULL;
 }
 
 
 LInstruction* LChunkBuilder::DoDeoptimize(HDeoptimize* instr) {
   return AssignEnvironment(new(zone()) LDeoptimize);
 }
 
 
+HBitwiseBinaryOperation* LChunkBuilder::CanTransformToShiftedOp(HValue* val,
+                                                                HValue** left) {
+  if (!val->representation().IsInteger32()) return NULL;
+  if (!(val->IsBitwise() || val->IsAdd() || val->IsSub())) return NULL;
+
+  HBinaryOperation* hinstr = HBinaryOperation::cast(val);
+  HValue* hleft = hinstr->left();
+  HValue* hright = hinstr->right();
+  ASSERT(hleft->representation().Equals(hinstr->representation()));
+  ASSERT(hright->representation().Equals(hinstr->representation()));
+
+  if ((hright->IsConstant() &&
+       LikelyFitsImmField(hinstr, HConstant::cast(hright)->Integer32Value())) ||
+      (hinstr->IsCommutative() && hleft->IsConstant() &&
+       LikelyFitsImmField(hinstr, HConstant::cast(hleft)->Integer32Value()))) {
+    // The constant operand will likely fit in the immediate field. We are
+    // better off with
+    //     mov r1, r2 LSL #imm
+    //     add r0, r1, #imm2
+    // than with
+    //     mov r5, #imm2
+    //     add r0, r5, r2 LSL #imm
+    return NULL;
+  }
+
+  HBitwiseBinaryOperation* shift = NULL;
+  // TODO(aleram): We will miss situations where a shift operation is used by
+  // different instructions both as a left and right operands.
+  if (hright->IsBitwiseBinaryShift() &&
+      HBitwiseBinaryOperation::cast(hright)->right()->IsConstant()) {
+    shift = HBitwiseBinaryOperation::cast(hright);
+    if (left != NULL) {
+      *left = hleft;
+    }
+  } else if (hinstr->IsCommutative() &&
+             hleft->IsBitwiseBinaryShift() &&
+             HBitwiseBinaryOperation::cast(hleft)->right()->IsConstant()) {
+    shift = HBitwiseBinaryOperation::cast(hleft);
+    if (left != NULL) {
+      *left = hright;
+    }
+  } else {
+    return NULL;
+  }
+
+  if ((JSShiftAmountFromHConstant(shift->right()) == 0) && shift->IsShr()) {
+    // Logical shifts right by zero can deoptimize.
+    return NULL;
+  }
+
+  return shift;
+}
+
+
+bool LChunkBuilder::ShiftCanBeOptimizedAway(HBitwiseBinaryOperation* shift) {
+  if (!shift->representation().IsInteger32()) {
+    return false;
+  }
+  for (HUseIterator it(shift->uses()); !it.Done(); it.Advance()) {
+    if (shift != CanTransformToShiftedOp(it.value())) {
+      return false;
+    }
+  }
+  return true;
+}
+
+
+LInstruction* LChunkBuilder::TryDoOpWithShiftedRightOperand(
+    HBinaryOperation* instr) {
+  HValue* left;
+  HBitwiseBinaryOperation* shift = CanTransformToShiftedOp(instr, &left);
+
+  if ((shift != NULL) && ShiftCanBeOptimizedAway(shift)) {
+    return DoShiftedBinaryOp(instr, left, shift);
+  }
+  return NULL;
+}
+
+
+LInstruction* LChunkBuilder::DoShiftedBinaryOp(
+    HBinaryOperation* hinstr, HValue* hleft, HBitwiseBinaryOperation* hshift) {
+  ASSERT(hshift->IsBitwiseBinaryShift());
+  ASSERT(!hshift->IsShr() || (JSShiftAmountFromHConstant(hshift->right()) > 0));
+
+  LTemplateResultInstruction<1>* res;
+  LOperand* left = UseRegisterAtStart(hleft);
+  LOperand* right = UseRegisterAtStart(hshift->left());
+  LOperand* shift_amount = UseConstant(hshift->right());
+  ShiftOp shift_op;
+  switch (hshift->opcode()) {
+    case HValue::kShl: shift_op = LSL; break;
+    case HValue::kShr: shift_op = LSR; break;
+    case HValue::kSar: shift_op = ASR; break;
+    default: UNREACHABLE(); shift_op = NO_SHIFT;
+  }
+
+  if (hinstr->IsBitwise()) {
+    res = new(zone()) LBitI(left, right, shift_op, shift_amount);
+  } else if (hinstr->IsAdd()) {
+    res = new(zone()) LAddI(left, right, shift_op, shift_amount);
+  } else {
+    ASSERT(hinstr->IsSub());
+    res = new(zone()) LSubI(left, right, shift_op, shift_amount);
+  }
+  if (hinstr->CheckFlag(HValue::kCanOverflow)) {
+    AssignEnvironment(res);
+  }
+  return DefineAsRegister(res);
+}
+
+
 LInstruction* LChunkBuilder::DoShift(Token::Value op,
                                      HBitwiseBinaryOperation* instr) {
   if (instr->representation().IsSmiOrInteger32()) {
     ASSERT(instr->left()->representation().Equals(instr->representation()));
     ASSERT(instr->right()->representation().Equals(instr->representation()));
+
+    if (ShiftCanBeOptimizedAway(instr)) {
+      return NULL;
+    }
+
     LOperand* left = UseRegisterAtStart(instr->left());
 
     HValue* right_value = instr->right();
     LOperand* right = NULL;
     int constant_value = 0;
     bool does_deopt = false;
     if (right_value->IsConstant()) {
       HConstant* constant = HConstant::cast(right_value);
       right = chunk_->DefineConstantOperand(constant);
       constant_value = constant->Integer32Value() & 0x1f;

[ulan, 2014/06/10 11:53:37]

Use JSShiftAmountFromHConstant?

[Alexandre Rames, 2014/06/11 10:19:40]

Done.

       // Left shifts can deoptimize if we shift by > 0 and the result cannot be
       // truncated to smi.
       if (instr->representation().IsSmi() && constant_value > 0) {
         does_deopt = !instr->CheckUsesForFlag(HValue::kTruncatingToSmi);
       }
     } else {
       right = UseRegisterAtStart(right_value);
     }
 
     // Shift operations can only deoptimize if we do a logical shift
@@ skipping 539 matching lines @@
   return DoShift(Token::SHL, instr);
 }
 
 
 LInstruction* LChunkBuilder::DoBitwise(HBitwise* instr) {
   if (instr->representation().IsSmiOrInteger32()) {
     ASSERT(instr->left()->representation().Equals(instr->representation()));
     ASSERT(instr->right()->representation().Equals(instr->representation()));
     ASSERT(instr->CheckFlag(HValue::kTruncatingToInt32));
 
+    LInstruction* shifted_operation = TryDoOpWithShiftedRightOperand(instr);
+    if (shifted_operation != NULL) {
+      return shifted_operation;
+    }
+
     LOperand* left = UseRegisterAtStart(instr->BetterLeftOperand());
     LOperand* right = UseOrConstantAtStart(instr->BetterRightOperand());
     return DefineAsRegister(new(zone()) LBitI(left, right));
   } else {
     return DoArithmeticT(instr->op(), instr);
   }
 }
 
 
 LInstruction* LChunkBuilder::DoDivByPowerOf2I(HDiv* instr) {
@@ skipping 263 matching lines @@
     return DoArithmeticT(Token::MUL, instr);
   }
 }
 
 
 LInstruction* LChunkBuilder::DoSub(HSub* instr) {
   if (instr->representation().IsSmiOrInteger32()) {
     ASSERT(instr->left()->representation().Equals(instr->representation()));
     ASSERT(instr->right()->representation().Equals(instr->representation()));
 
+    LInstruction* shifted_operation = TryDoOpWithShiftedRightOperand(instr);
+    if (shifted_operation != NULL) {
+      return shifted_operation;
+    }
+
     if (instr->left()->IsConstant()) {
       // If lhs is constant, do reverse subtraction instead.
       return DoRSub(instr);
     }
 
     LOperand* left = UseRegisterAtStart(instr->left());
     LOperand* right = UseOrConstantAtStart(instr->right());
     LSubI* sub = new(zone()) LSubI(left, right);
     LInstruction* result = DefineAsRegister(sub);
     if (instr->CheckFlag(HValue::kCanOverflow)) {
@@ skipping 47 matching lines @@
   return DefineSameAsFirst(new(zone()) LMultiplySubD(minuend_op,
                                                      multiplier_op,
                                                      multiplicand_op));
 }
 
 
 LInstruction* LChunkBuilder::DoAdd(HAdd* instr) {
   if (instr->representation().IsSmiOrInteger32()) {
     ASSERT(instr->left()->representation().Equals(instr->representation()));
     ASSERT(instr->right()->representation().Equals(instr->representation()));
+
+    LInstruction* shifted_operation = TryDoOpWithShiftedRightOperand(instr);
+    if (shifted_operation != NULL) {
+      return shifted_operation;
+    }
+
     LOperand* left = UseRegisterAtStart(instr->BetterLeftOperand());
     LOperand* right = UseOrConstantAtStart(instr->BetterRightOperand());
     LAddI* add = new(zone()) LAddI(left, right);
     LInstruction* result = DefineAsRegister(add);
     if (instr->CheckFlag(HValue::kCanOverflow)) {
       result = AssignEnvironment(result);
     }
     return result;
   } else if (instr->representation().IsExternal()) {
     ASSERT(instr->left()->representation().IsExternal());
@@ skipping 960 matching lines @@
 
 LInstruction* LChunkBuilder::DoLoadFieldByIndex(HLoadFieldByIndex* instr) {
   LOperand* object = UseRegister(instr->object());
   LOperand* index = UseTempRegister(instr->index());
   LLoadFieldByIndex* load = new(zone()) LLoadFieldByIndex(object, index);
   LInstruction* result = DefineSameAsFirst(load);
   return AssignPointerMap(result);
 }
 
 } }  // namespace v8::internal