Avoid re-tagging of the index register in optimized byte array access.

runtime/vm/intermediate_language_x64.cc

 // Copyright (c) 2013, 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_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "lib/error.h"
@@ skipping 1002 matching lines @@
   }
 }
 
 
 LocationSummary* LoadIndexedInstr::MakeLocationSummary() const {
   const intptr_t kNumInputs = 2;
   const intptr_t kNumTemps = 0;
   LocationSummary* locs =
       new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
   locs->set_in(0, Location::RequiresRegister());
-  // The smi index is either untagged and tagged again at the end of the
-  // operation (element size == 1), or it is left smi tagged (for all element
-  // sizes > 1).
-  locs->set_in(1, CanBeImmediateIndex(index(), class_id())
-                    ? Location::RegisterOrSmiConstant(index())
-                    : Location::RequiresRegister());
+  // The smi index is either untagged (element size == 1), or it is left smi
+  // tagged (for all element sizes > 1).
+  if (index_scale() == 1) {
+    locs->set_in(1, CanBeImmediateIndex(index(), class_id())
+                      ? Location::Constant(
+                          index()->definition()->AsConstant()->value())
+                      : Location::WritableRegister());
+  } else {
+    locs->set_in(1, CanBeImmediateIndex(index(), class_id())
+                      ? Location::Constant(
+                          index()->definition()->AsConstant()->value())
+                      : Location::RequiresRegister());
+  }
   if (representation() == kUnboxedDouble) {
     locs->set_out(Location::RequiresFpuRegister());
   } else {
     locs->set_out(Location::RequiresRegister());
   }
   return locs;
 }
 
 
 void LoadIndexedInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
@@ skipping 10 matching lines @@
             class_id(), index_scale(), result,
             Smi::Cast(index.constant()).Value());
     ASSERT(index_scale() == 1);
     if (index.IsRegister()) {
       __ SmiUntag(index.reg());
     }
     __ movq(result,
             FieldAddress(array, ExternalUint8Array::data_offset()));
     __ movzxb(result, element_address);
     __ SmiTag(result);
-    if (index.IsRegister()) {
-      __ SmiTag(index.reg());  // Re-tag.
-    }
     return;
   }
 
   FieldAddress element_address = index.IsRegister()
       ? FlowGraphCompiler::ElementAddressForRegIndex(
           class_id(), index_scale(), array, index.reg())
       : FlowGraphCompiler::ElementAddressForIntIndex(
           class_id(), index_scale(), array,
           Smi::Cast(index.constant()).Value());
 
   if (representation() == kUnboxedDouble) {
     if ((index_scale() == 1) && index.IsRegister()) {
       __ SmiUntag(index.reg());
     }
 
     XmmRegister result = locs()->out().fpu_reg();
     if (class_id() == kFloat32ArrayCid) {
       // Load single precision float.
       __ movss(result, element_address);
       // Promote to double.
       __ cvtss2sd(result, locs()->out().fpu_reg());
     } else {
       ASSERT(class_id() == kFloat64ArrayCid);
       __ movsd(result, element_address);
     }
-
-    if ((index_scale() == 1) && index.IsRegister()) {
-        __ SmiTag(index.reg());  // Re-tag.
-    }
     return;
   }
 
   if ((index_scale() == 1) && index.IsRegister()) {
     __ SmiUntag(index.reg());
   }
   Register result = locs()->out().reg();
   switch (class_id()) {
     case kInt8ArrayCid:
     case kUint8ArrayCid:
@@ skipping 21 matching lines @@
       break;
     case kUint32ArrayCid:
       __ movl(result, element_address);
       __ SmiTag(result);
       break;
     default:
       ASSERT((class_id() == kArrayCid) || (class_id() == kImmutableArrayCid));
       __ movq(result, element_address);
       break;
   }
-  if ((index_scale() == 1) && index.IsRegister()) {
-      __ SmiTag(index.reg());  // Re-tag.
-  }
 }
 
 
 Representation StoreIndexedInstr::RequiredInputRepresentation(
     intptr_t idx) const {
   if ((idx == 0) || (idx == 1)) return kTagged;
   ASSERT(idx == 2);
   switch (class_id_) {
     case kArrayCid:
     case kInt8ArrayCid:
@@ skipping 12 matching lines @@
       return kTagged;
   }
 }
 
 
 LocationSummary* StoreIndexedInstr::MakeLocationSummary() const {
   const intptr_t kNumInputs = 3;
   const intptr_t kNumTemps = 0;
   LocationSummary* locs =
       new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
-  // The smi index is either untagged and tagged again at the end of the
-  // operation (element size == 1), or it is left smi tagged (for all element
-  // sizes > 1).
   locs->set_in(0, Location::RequiresRegister());
-  locs->set_in(1, CanBeImmediateIndex(index(), class_id())
-                    ? Location::RegisterOrSmiConstant(index())
-                    : Location::RequiresRegister());
+  // The smi index is either untagged (element size == 1), or it is left smi
+  // tagged (for all element sizes > 1).
+  intptr_t index_scale = FlowGraphCompiler::ElementSizeFor(class_id());
+  if (index_scale == 1) {
+    locs->set_in(1, CanBeImmediateIndex(index(), class_id())
+                      ? Location::Constant(
+                          index()->definition()->AsConstant()->value())
+                      : Location::WritableRegister());
+  } else {
+    locs->set_in(1, CanBeImmediateIndex(index(), class_id())
+                      ? Location::Constant(
+                          index()->definition()->AsConstant()->value())
+                      : Location::RequiresRegister());
+  }
   switch (class_id()) {
     case kArrayCid:
       locs->set_in(2, ShouldEmitStoreBarrier()
                         ? Location::WritableRegister()
                         : Location::RegisterOrConstant(value()));
       break;
     case kInt8ArrayCid:
     case kUint8ArrayCid:
     case kUint8ClampedArrayCid:
       // TODO(fschneider): Add location constraint for byte registers (RAX,
@@ skipping 56 matching lines @@
       }
       if (locs()->in(2).IsConstant()) {
         const Smi& constant = Smi::Cast(locs()->in(2).constant());
         __ movb(element_address,
                 Immediate(static_cast<int8_t>(constant.Value())));
       } else {
         ASSERT(locs()->in(2).reg() == RAX);
         __ SmiUntag(RAX);
         __ movb(element_address, RAX);
       }
-      if (index.IsRegister()) {
-        __ SmiTag(index.reg());  // Re-tag.
-      }
       break;
     case kUint8ClampedArrayCid: {
       if (index.IsRegister()) {
         __ SmiUntag(index.reg());
       }
       if (locs()->in(2).IsConstant()) {
         const Smi& constant = Smi::Cast(locs()->in(2).constant());
         intptr_t value = constant.Value();
         // Clamp to 0x0 or 0xFF respectively.
         if (value > 0xFF) {
@@ skipping 11 matching lines @@
         __ j(BELOW_EQUAL, &store_value, Assembler::kNearJump);
         // Clamp to 0x0 or 0xFF respectively.
         __ j(GREATER, &store_0xff);
         __ xorq(RAX, RAX);
         __ jmp(&store_value, Assembler::kNearJump);
         __ Bind(&store_0xff);
         __ movq(RAX, Immediate(0xFF));
         __ Bind(&store_value);
         __ movb(element_address, RAX);
       }
-      if (index.IsRegister()) {
-        __ SmiTag(index.reg());  // Re-tag.
-      }
       break;
     }
     case kInt16ArrayCid:
     case kUint16ArrayCid: {
       Register value = locs()->in(2).reg();
       __ SmiUntag(value);
       __ movw(element_address, value);
       break;
     }
     case kInt32ArrayCid:
@@ skipping 910 matching lines @@
                                slow_path->entry_label(),
                                Assembler::kFarJump,
                                out_reg);
   __ Bind(slow_path->exit_label());
   __ movsd(FieldAddress(out_reg, Double::value_offset()), value);
 }
 
 
 LocationSummary* UnboxDoubleInstr::MakeLocationSummary() const {
   const intptr_t kNumInputs = 1;
-  const intptr_t kNumTemps = CanDeoptimize() ? 1 : 0;
+  const intptr_t kNumTemps = 0;
   LocationSummary* summary =
       new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
-  summary->set_in(0, Location::RequiresRegister());
-  if (CanDeoptimize()) summary->set_temp(0, Location::RequiresRegister());
+  const bool needs_writable_input = (value()->ResultCid() != kDoubleCid);
+  summary->set_in(0, needs_writable_input
+                     ? Location::WritableRegister()
+                     : Location::RequiresRegister());
   summary->set_out(Location::RequiresFpuRegister());
   return summary;
 }
 
 
 void UnboxDoubleInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   const intptr_t value_cid = value()->ResultCid();
   const Register value = locs()->in(0).reg();
   const XmmRegister result = locs()->out().fpu_reg();
 
   if (value_cid == kDoubleCid) {
     __ movsd(result, FieldAddress(value, Double::value_offset()));
   } else if (value_cid == kSmiCid) {
     __ SmiUntag(value);  // Untag input before conversion.
     __ cvtsi2sd(result, value);
-    __ SmiTag(value);  // Restore input register.
   } else {
     Label* deopt = compiler->AddDeoptStub(deopt_id_, kDeoptBinaryDoubleOp);
-    compiler->LoadDoubleOrSmiToFpu(result,
-                                   value,
-                                   locs()->temp(0).reg(),
-                                   deopt);
+    Label is_smi, done;
+    __ testq(value, Immediate(kSmiTagMask));
+    __ j(ZERO, &is_smi);
+    __ CompareClassId(value, kDoubleCid);
+    __ j(NOT_EQUAL, deopt);
+    __ movsd(result, FieldAddress(value, Double::value_offset()));
+    __ jmp(&done);
+    __ Bind(&is_smi);
+    __ SmiUntag(value);
+    __ cvtsi2sd(result, value);
+    __ Bind(&done);
   }
 }
 
 
 LocationSummary* BinaryDoubleOpInstr::MakeLocationSummary() const {
   const intptr_t kNumInputs = 2;
   const intptr_t kNumTemps = 0;
   LocationSummary* summary =
       new LocationSummary(kNumInputs, kNumTemps, LocationSummary::kNoCall);
   summary->set_in(0, Location::RequiresFpuRegister());
@@ skipping 792 matching lines @@
                          PcDescriptors::kOther,
                          locs());
   __ Drop(2);  // Discard type arguments and receiver.
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64