[Turbofan] Add concept of FP register aliasing on ARM 32.

src/compiler/instruction.cc

 // Copyright 2014 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/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/instruction.h"
 #include "src/compiler/schedule.h"
 #include "src/compiler/state-values-utils.h"
 
@@ skipping 46 matching lines @@
     case kOverflow:
     case kNotOverflow:
     case kUnorderedEqual:
     case kUnorderedNotEqual:
       return condition;
   }
   UNREACHABLE();
   return condition;
 }
 
-bool InstructionOperand::InterferesWith(const InstructionOperand& that) const {
-  return EqualsCanonicalized(that);
+bool InstructionOperand::InterferesWith(const InstructionOperand& other) const {
+  if (kSimpleFPAliasing || !this->IsFPLocationOperand() ||
+      !other.IsFPLocationOperand())
+    return EqualsCanonicalized(other);
+  // Aliasing is complex and both operands are fp locations.
+  const LocationOperand& loc = *LocationOperand::cast(this);
+  const LocationOperand& other_loc = LocationOperand::cast(other);
+  LocationOperand::LocationKind kind = loc.location_kind();
+  LocationOperand::LocationKind other_kind = other_loc.location_kind();
+  if (kind != other_kind) return false;
+  MachineRepresentation rep = loc.representation();
+  MachineRepresentation other_rep = other_loc.representation();
+  if (rep == other_rep) return EqualsCanonicalized(other);
+  if (kind == LocationOperand::REGISTER) {
+    // FP register-register interference.
+    return GetRegConfig()->AreAliases(rep, loc.register_code(), other_rep,
+                                      other_loc.register_code());
+  } else {
+    // FP slot-slot interference. Slots of different FP reps can alias because
+    // the gap resolver may break a move into 2 or 4 equivalent smaller moves.
+    DCHECK_EQ(LocationOperand::STACK_SLOT, kind);
+    int index_hi = loc.index();
+    const int kBaseRep = static_cast<int>(MachineRepresentation::kFloat32);
+    int index_lo = index_hi - (1 << (static_cast<int>(rep) - kBaseRep)) + 1;

[Jarin, 2016/10/18 11:44:28]

Could we express this in terms of ElementSizeLog2Of, please?

E.g., 

int index_lo = index_hi - (1 << (ElementSizeLog2Of(rep) - kPointerSizeLog2)) + 1

or 

int index_lo = index_hi - (1 << ElementSizeLog2Of(rep)) / kPointerSize + 1

[bbudge, 2016/10/19 00:32:21]

Done. (both places)

+    int other_index_hi = other_loc.index();
+    int other_index_lo =
+        other_index_hi - (1 << (static_cast<int>(other_rep) - kBaseRep)) + 1;
+    return !(other_index_hi < index_lo || index_hi < other_index_lo);

[bbudge, 2016/10/19 00:32:21]

I also De-morgan'ed this boolean expression.

+  }
+  return false;
 }
 
 void InstructionOperand::Print(const RegisterConfiguration* config) const {
   OFStream os(stdout);
   PrintableInstructionOperand wrapper;
   wrapper.register_configuration_ = config;
   wrapper.op_ = *this;
   os << wrapper << std::endl;
 }
 
@@ skipping 146 matching lines @@
 }
 
 
 bool ParallelMove::IsRedundant() const {
   for (MoveOperands* move : *this) {
     if (!move->IsRedundant()) return false;
   }
   return true;
 }
 
-
-MoveOperands* ParallelMove::PrepareInsertAfter(MoveOperands* move) const {
+void ParallelMove::PrepareInsertAfter(
+    MoveOperands* move, ZoneVector<MoveOperands*>* to_eliminate) const {
+  bool no_aliasing =
+      kSimpleFPAliasing || !move->destination().IsFPLocationOperand();
   MoveOperands* replacement = nullptr;
-  MoveOperands* to_eliminate = nullptr;
+  MoveOperands* eliminated = nullptr;
   for (MoveOperands* curr : *this) {
     if (curr->IsEliminated()) continue;
     if (curr->destination().EqualsCanonicalized(move->source())) {
+      // We must replace move's source with curr's destination in order to
+      // insert it into this ParallelMove.
       DCHECK(!replacement);
       replacement = curr;
-      if (to_eliminate != nullptr) break;
-    } else if (curr->destination().EqualsCanonicalized(move->destination())) {
-      DCHECK(!to_eliminate);
-      to_eliminate = curr;
-      if (replacement != nullptr) break;
+      if (no_aliasing && eliminated != nullptr) break;
+    } else if (curr->destination().InterferesWith(move->destination())) {
+      // We can eliminate curr, since move overwrites at least a part of its
+      // destination, implying its value is no longer live.
+      eliminated = curr;
+      to_eliminate->push_back(curr);
+      if (no_aliasing && replacement != nullptr) break;
     }
   }
-  DCHECK_IMPLIES(replacement == to_eliminate, replacement == nullptr);
   if (replacement != nullptr) move->set_source(replacement->source());
-  return to_eliminate;
 }
 
-
 ExplicitOperand::ExplicitOperand(LocationKind kind, MachineRepresentation rep,
                                  int index)
     : LocationOperand(EXPLICIT, kind, rep, index) {
   DCHECK_IMPLIES(kind == REGISTER && !IsFloatingPoint(rep),
                  GetRegConfig()->IsAllocatableGeneralCode(index));
   DCHECK_IMPLIES(kind == REGISTER && rep == MachineRepresentation::kFloat32,
                  GetRegConfig()->IsAllocatableFloatCode(index));
   DCHECK_IMPLIES(kind == REGISTER && (rep == MachineRepresentation::kFloat64),
                  GetRegConfig()->IsAllocatableDoubleCode(index));
 }
@@ skipping 769 matching lines @@
   for (int i = 0; i < code.InstructionBlockCount(); i++) {
     printable_block.block_ = code.InstructionBlockAt(RpoNumber::FromInt(i));
     os << printable_block;
   }
   return os;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8