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

src/compiler/instruction.cc

Index: src/compiler/instruction.cc
diff --git a/src/compiler/instruction.cc b/src/compiler/instruction.cc
index 39ea47689c963e1989c5ba7f92269e08c4c64c3c..42527c1636092d01df8f2ec296052f8d6fb5f502 100644
--- a/src/compiler/instruction.cc
+++ b/src/compiler/instruction.cc
@@ -64,8 +64,36 @@ FlagsCondition CommuteFlagsCondition(FlagsCondition condition) {
   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 {
@@ -232,28 +260,31 @@ bool ParallelMove::IsRedundant() const {
   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) {