Generate better ARM64 code for indexed loads and stores.

runtime/vm/intermediate_language_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_ARM64.
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/dart_entry.h"
@@ skipping 966 matching lines @@
       return kUnboxedFloat32x4;
     case kTypedDataFloat64x2ArrayCid:
       return kUnboxedFloat64x2;
     default:
       UNIMPLEMENTED();
       return kTagged;
   }
 }
 
 
+static bool CanBeImmediateIndex(Value* value, intptr_t cid, bool is_external) {
+  ConstantInstr* constant = value->definition()->AsConstant();
+  if ((constant == NULL) || !constant->value().IsSmi()) {
+    return false;
+  }
+  const int64_t index = Smi::Cast(constant->value()).AsInt64Value();
+  const intptr_t scale = Instance::ElementSizeFor(cid);
+  const int64_t offset = index * scale +
+      (is_external ? 0 : (Instance::DataOffsetFor(cid) - kHeapObjectTag));
+  if (!Utils::IsInt(32, offset)) {
+    return false;
+  }
+  return Address::CanHoldOffset(static_cast<int32_t>(offset),
+                                Address::Offset,
+                                Address::OperandSizeFor(cid));
+}
+
+
 LocationSummary* LoadIndexedInstr::MakeLocationSummary(Isolate* isolate,
                                                        bool opt) const {
   const intptr_t kNumInputs = 2;
   const intptr_t kNumTemps = 0;
   LocationSummary* locs = new(isolate) LocationSummary(
       isolate, kNumInputs, kNumTemps, LocationSummary::kNoCall);
   locs->set_in(0, Location::RequiresRegister());
-  // The smi index is either untagged (element size == 1), or it is left smi
-  // tagged (for all element sizes > 1).
-  // TODO(regis): Revisit and see if the index can be immediate.
-  locs->set_in(1, Location::WritableRegister());
+  if (CanBeImmediateIndex(index(), class_id(), IsExternal())) {
+    locs->set_in(1, Location::Constant(index()->BoundConstant()));
+  } else {
+    locs->set_in(1, Location::RequiresRegister());
+  }
   if ((representation() == kUnboxedDouble)    ||
       (representation() == kUnboxedFloat32x4) ||
       (representation() == kUnboxedInt32x4)   ||
       (representation() == kUnboxedFloat64x2)) {
     locs->set_out(0, Location::RequiresFpuRegister());
   } else {
     locs->set_out(0, Location::RequiresRegister());
   }
   return locs;
 }
 
 
+static Address ElementAddressForIntIndex(bool is_external,
+                                         intptr_t cid,
+                                         intptr_t index_scale,
+                                         Register array,
+                                         intptr_t index) {
+  const int64_t offset = index * index_scale +
+      (is_external ? 0 : (Instance::DataOffsetFor(cid) - kHeapObjectTag));
+  ASSERT(Utils::IsInt(32, offset));
+  const OperandSize size = Address::OperandSizeFor(cid);
+  ASSERT(Address::CanHoldOffset(offset, Address::Offset, size));
+  return Address(array, static_cast<int32_t>(offset), Address::Offset, size);
+}
+
+
+static Address ElementAddressForRegIndex(Assembler* assembler,
+                                         bool is_load,
+                                         bool is_external,
+                                         intptr_t cid,
+                                         intptr_t index_scale,
+                                         Register array,
+                                         Register index) {
+  // Note that index is expected smi-tagged, (i.e, LSL 1) for all arrays.
+  const intptr_t shift = Utils::ShiftForPowerOfTwo(index_scale) - kSmiTagShift;
+  const int32_t offset =
+      is_external ? 0 : (Instance::DataOffsetFor(cid) - kHeapObjectTag);
+  ASSERT(array != TMP);
+  ASSERT(index != TMP);
+  const Register base = is_load ? TMP : index;
+  if ((offset == 0) && (shift == 0)) {
+    return Address(array, index, UXTX, Address::Unscaled);
+  } else if (shift < 0) {
+    ASSERT(shift == -1);
+    assembler->add(base, array, Operand(index, ASR, 1));
+  } else {
+    assembler->add(base, array, Operand(index, LSL, shift));
+  }
+  const OperandSize size = Address::OperandSizeFor(cid);
+  ASSERT(Address::CanHoldOffset(offset, Address::Offset, size));
+  return Address(base, offset, Address::Offset, size);
+}
+
+
 void LoadIndexedInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  // The array register points to the backing store for external arrays.
   const Register array = locs()->in(0).reg();
-  ASSERT(locs()->in(1).IsRegister());  // TODO(regis): Revisit.
-  const Register index = locs()->in(1).reg();
+  const Location index = locs()->in(1);
 
-  Address element_address(kNoRegister, 0);
-
-  // The array register points to the backing store for external arrays.
-  intptr_t offset = 0;
-  if (!IsExternal()) {
-    ASSERT(this->array()->definition()->representation() == kTagged);
-    offset = Instance::DataOffsetFor(class_id()) - kHeapObjectTag;
-  }
-
-  // Note that index is expected smi-tagged, (i.e, times 2) for all arrays
-  // with index scale factor > 1. E.g., for Uint8Array and OneByteString the
-  // index is expected to be untagged before accessing.
-  ASSERT(kSmiTagShift == 1);
-  switch (index_scale()) {
-    case 1:
-      __ add(index, array, Operand(index, ASR, kSmiTagSize));
-      element_address = Address(index, offset);
-      break;
-    case 2:
-      if (offset != 0) {
-        __ add(index, array, Operand(index));
-        element_address = Address(index, offset);
-      } else {
-        element_address = Address(array, index, UXTX, Address::Unscaled);
-      }
-      break;
-    case 4:
-      __ add(index, array, Operand(index, LSL, 1));
-      element_address = Address(index, offset);
-      break;
-    case 8:
-      __ add(index, array, Operand(index, LSL, 2));
-      element_address = Address(index, offset);
-      break;
-    case 16:
-      __ add(index, array, Operand(index, LSL, 3));
-      element_address = Address(index, offset);
-      break;
-    default:
-      UNREACHABLE();
-  }
+  Address element_address = index.IsRegister()
+      ? ElementAddressForRegIndex(compiler->assembler(),
+                                  true,  // Load.
+                                  IsExternal(), class_id(), index_scale(),
+                                  array, index.reg())
+      : ElementAddressForIntIndex(IsExternal(), class_id(), index_scale(),
+                                  array, Smi::Cast(index.constant()).Value());
+  // Warning: element_address may use register TMP as base.
 
   if ((representation() == kUnboxedDouble)    ||
       (representation() == kUnboxedFloat32x4) ||
       (representation() == kUnboxedInt32x4)   ||
       (representation() == kUnboxedFloat64x2)) {
     const VRegister result = locs()->out(0).fpu_reg();
     switch (class_id()) {
       case kTypedDataFloat32ArrayCid:
         // Load single precision float.
         __ fldrs(result, element_address);
         break;
       case kTypedDataFloat64ArrayCid:
         // Load double precision float.
         __ fldrd(result, element_address);
         break;
       case kTypedDataFloat64x2ArrayCid:
       case kTypedDataInt32x4ArrayCid:
       case kTypedDataFloat32x4ArrayCid:
         __ fldrq(result, element_address);
         break;
+      default:
+        UNREACHABLE();
     }
     return;
   }
 
   const Register result = locs()->out(0).reg();
   switch (class_id()) {
     case kTypedDataInt8ArrayCid:
       ASSERT(index_scale() == 1);
       __ ldr(result, element_address, kByte);
       __ SmiTag(result);
@@ skipping 67 matching lines @@
 }
 
 
 LocationSummary* StoreIndexedInstr::MakeLocationSummary(Isolate* isolate,
                                                         bool opt) const {
   const intptr_t kNumInputs = 3;
   const intptr_t kNumTemps = 0;
   LocationSummary* locs = new(isolate) LocationSummary(
       isolate, kNumInputs, kNumTemps, LocationSummary::kNoCall);
   locs->set_in(0, Location::RequiresRegister());
-  // The smi index is either untagged (element size == 1), or it is left smi
-  // tagged (for all element sizes > 1).
-  // TODO(regis): Revisit and see if the index can be immediate.
-  locs->set_in(1, Location::WritableRegister());
+  if (CanBeImmediateIndex(index(), class_id(), IsExternal())) {
+    locs->set_in(1, Location::Constant(index()->BoundConstant()));
+  } else {
+    locs->set_in(1, Location::WritableRegister());
+  }
   switch (class_id()) {
     case kArrayCid:
       locs->set_in(2, ShouldEmitStoreBarrier()
                         ? Location::WritableRegister()
                         : Location::RegisterOrConstant(value()));
       break;
     case kExternalTypedDataUint8ArrayCid:
     case kExternalTypedDataUint8ClampedArrayCid:
     case kTypedDataInt8ArrayCid:
     case kTypedDataUint8ArrayCid:
@@ skipping 18 matching lines @@
       break;
     default:
       UNREACHABLE();
       return NULL;
   }
   return locs;
 }
 
 
 void StoreIndexedInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
+  // The array register points to the backing store for external arrays.
   const Register array = locs()->in(0).reg();
-  ASSERT(locs()->in(1).IsRegister());  // TODO(regis): Revisit.
-  const Register index = locs()->in(1).reg();
+  const Location index = locs()->in(1);
 
-  Address element_address(kNoRegister, 0);
-
-  // The array register points to the backing store for external arrays.
-  intptr_t offset = 0;
-  if (!IsExternal()) {
-    ASSERT(this->array()->definition()->representation() == kTagged);
-    offset = Instance::DataOffsetFor(class_id()) - kHeapObjectTag;
-  }
-
-  // Note that index is expected smi-tagged, (i.e, times 2) for all arrays
-  // with index scale factor > 1. E.g., for Uint8Array and OneByteString the
-  // index is expected to be untagged before accessing.
-  ASSERT(kSmiTagShift == 1);
-  switch (index_scale()) {
-    case 1: {
-      __ add(index, array, Operand(index, ASR, kSmiTagSize));
-      element_address = Address(index, offset);
-      break;
-    }
-    case 2: {
-      if (offset != 0) {
-        __ add(index, array, Operand(index));
-        element_address = Address(index, offset);
-      } else {
-        element_address = Address(array, index, UXTX, Address::Unscaled);
-      }
-      break;
-    }
-    case 4: {
-      __ add(index, array, Operand(index, LSL, 1));
-      element_address = Address(index, offset);
-      break;
-    }
-    case 8: {
-      __ add(index, array, Operand(index, LSL, 2));
-      element_address = Address(index, offset);
-      break;
-    }
-    case 16: {
-      __ add(index, array, Operand(index, LSL, 3));
-      element_address = Address(index, offset);
-      break;
-    }
-    default:
-      UNREACHABLE();
-  }
+  Address element_address = index.IsRegister()
+      ? ElementAddressForRegIndex(compiler->assembler(),
+                                  false,  // Store.
+                                  IsExternal(), class_id(), index_scale(),
+                                  array, index.reg())
+      : ElementAddressForIntIndex(IsExternal(), class_id(), index_scale(),
+                                  array, Smi::Cast(index.constant()).Value());
 
   switch (class_id()) {
     case kArrayCid:
       if (ShouldEmitStoreBarrier()) {
         const Register value = locs()->in(2).reg();
         __ StoreIntoObject(array, element_address, value);
       } else if (locs()->in(2).IsConstant()) {
         const Object& constant = locs()->in(2).constant();
         __ StoreIntoObjectNoBarrier(array, element_address, constant);
       } else {
@@ skipping 4144 matching lines @@
   compiler->GenerateCall(token_pos(),
                          &label,
                          PcDescriptors::kOther,
                          locs());
   __ Drop(ArgumentCount());  // Discard arguments.
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64