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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "jit/MoveResolver.h"
+
+#include "mozilla/ScopeExit.h"
+
+#include "jit/MacroAssembler.h"
+#include "jit/RegisterSets.h"
+
+using namespace js;
+using namespace js::jit;
+
+MoveOperand::MoveOperand(MacroAssembler& masm, const ABIArg& arg) : disp_(0) {
+ switch (arg.kind()) {
+ case ABIArg::GPR:
+ kind_ = Kind::Reg;
+ code_ = arg.gpr().code();
+ break;
+#ifdef JS_CODEGEN_REGISTER_PAIR
+ case ABIArg::GPR_PAIR:
+ kind_ = Kind::RegPair;
+ code_ = arg.evenGpr().code();
+ MOZ_ASSERT(code_ % 2 == 0);
+ MOZ_ASSERT(code_ + 1 == arg.oddGpr().code());
+ break;
+#endif
+ case ABIArg::FPU:
+ kind_ = Kind::FloatReg;
+ code_ = arg.fpu().code();
+ break;
+ case ABIArg::Stack:
+ kind_ = Kind::Memory;
+ if (IsHiddenSP(masm.getStackPointer())) {
+ MOZ_CRASH(
+ "Hidden SP cannot be represented as register code on this "
+ "platform");
+ } else {
+ code_ = AsRegister(masm.getStackPointer()).code();
+ }
+ disp_ = arg.offsetFromArgBase();
+ break;
+ case ABIArg::Uninitialized:
+ MOZ_CRASH("Uninitialized ABIArg kind");
+ }
+}
+
+MoveResolver::MoveResolver() : numCycles_(0), curCycles_(0) {}
+
+void MoveResolver::resetState() {
+ numCycles_ = 0;
+ curCycles_ = 0;
+}
+
+bool MoveResolver::addMove(const MoveOperand& from, const MoveOperand& to,
+ MoveOp::Type type) {
+ // Assert that we're not doing no-op moves.
+ MOZ_ASSERT(!(from == to));
+ PendingMove* pm = movePool_.allocate(from, to, type);
+ if (!pm) {
+ return false;
+ }
+ pending_.pushBack(pm);
+ return true;
+}
+
+// Given move (A -> B), this function attempts to find any move (B -> *) in the
+// pending move list, and returns the first one.
+MoveResolver::PendingMove* MoveResolver::findBlockingMove(
+ const PendingMove* last) {
+ for (PendingMoveIterator iter = pending_.begin(); iter != pending_.end();
+ iter++) {
+ PendingMove* other = *iter;
+
+ if (other->from().aliases(last->to())) {
+ // We now have pairs in the form (A -> X) (X -> y). The second pair
+ // blocks the move in the first pair, so return it.
+ return other;
+ }
+ }
+
+ // No blocking moves found.
+ return nullptr;
+}
+
+// Given move (A -> B), this function attempts to find any move (B -> *) in the
+// move list iterator, and returns the first one.
+// N.B. It is unclear if a single move can complete more than one cycle, so to
+// be conservative, this function operates on iterators, so the caller can
+// process all instructions that start a cycle.
+MoveResolver::PendingMove* MoveResolver::findCycledMove(
+ PendingMoveIterator* iter, PendingMoveIterator end,
+ const PendingMove* last) {
+ for (; *iter != end; (*iter)++) {
+ PendingMove* other = **iter;
+ if (other->from().aliases(last->to())) {
+ // We now have pairs in the form (A -> X) (X -> y). The second pair
+ // blocks the move in the first pair, so return it.
+ (*iter)++;
+ return other;
+ }
+ }
+ // No blocking moves found.
+ return nullptr;
+}
+
+#ifdef JS_CODEGEN_ARM
+static inline bool MoveIsDouble(const MoveOperand& move) {
+ if (!move.isFloatReg()) {
+ return false;
+ }
+ return move.floatReg().isDouble();
+}
+#endif
+
+#ifdef JS_CODEGEN_ARM
+static inline bool MoveIsSingle(const MoveOperand& move) {
+ if (!move.isFloatReg()) {
+ return false;
+ }
+ return move.floatReg().isSingle();
+}
+#endif
+
+#ifdef JS_CODEGEN_ARM
+bool MoveResolver::isDoubleAliasedAsSingle(const MoveOperand& move) {
+ if (!MoveIsDouble(move)) {
+ return false;
+ }
+
+ for (auto iter = pending_.begin(); iter != pending_.end(); ++iter) {
+ PendingMove* other = *iter;
+ if (other->from().aliases(move) && MoveIsSingle(other->from())) {
+ return true;
+ }
+ if (other->to().aliases(move) && MoveIsSingle(other->to())) {
+ return true;
+ }
+ }
+ return false;
+}
+#endif
+
+#ifdef JS_CODEGEN_ARM
+static MoveOperand SplitIntoLowerHalf(const MoveOperand& move) {
+ if (MoveIsDouble(move)) {
+ FloatRegister lowerSingle = move.floatReg().asSingle();
+ return MoveOperand(lowerSingle);
+ }
+
+ MOZ_ASSERT(move.isMemoryOrEffectiveAddress());
+ return move;
+}
+#endif
+
+#ifdef JS_CODEGEN_ARM
+static MoveOperand SplitIntoUpperHalf(const MoveOperand& move) {
+ if (MoveIsDouble(move)) {
+ FloatRegister lowerSingle = move.floatReg().asSingle();
+ FloatRegister upperSingle =
+ VFPRegister(lowerSingle.code() + 1, VFPRegister::Single);
+ return MoveOperand(upperSingle);
+ }
+
+ MOZ_ASSERT(move.isMemoryOrEffectiveAddress());
+ return MoveOperand(move.base(), move.disp() + sizeof(float));
+}
+#endif
+
+// Resolves the pending_ list to a list in orderedMoves_.
+bool MoveResolver::resolve() {
+ resetState();
+ orderedMoves_.clear();
+
+ // Upon return from this function, the pending_ list must be cleared.
+ auto clearPending = mozilla::MakeScopeExit([this]() { pending_.clear(); });
+
+#ifdef JS_CODEGEN_ARM
+ // Some of ARM's double registers alias two of its single registers,
+ // but the algorithm below assumes that every register can participate
+ // in at most one cycle. To satisfy the algorithm, any double registers
+ // that may conflict are split into their single-register halves.
+ //
+ // This logic is only applicable because ARM only uses registers d0-d15,
+ // all of which alias s0-s31. Double registers d16-d31 are unused.
+ // Therefore there is never a double move that cannot be split.
+ // If this changes in the future, the algorithm will have to be fixed.
+
+ bool splitDoubles = false;
+ for (auto iter = pending_.begin(); iter != pending_.end(); ++iter) {
+ PendingMove* pm = *iter;
+
+ if (isDoubleAliasedAsSingle(pm->from()) ||
+ isDoubleAliasedAsSingle(pm->to())) {
+ splitDoubles = true;
+ break;
+ }
+ }
+
+ if (splitDoubles) {
+ for (auto iter = pending_.begin(); iter != pending_.end(); ++iter) {
+ PendingMove* pm = *iter;
+
+ if (!MoveIsDouble(pm->from()) && !MoveIsDouble(pm->to())) {
+ continue;
+ }
+
+ MoveOperand fromLower = SplitIntoLowerHalf(pm->from());
+ MoveOperand toLower = SplitIntoLowerHalf(pm->to());
+
+ PendingMove* lower =
+ movePool_.allocate(fromLower, toLower, MoveOp::FLOAT32);
+ if (!lower) {
+ return false;
+ }
+
+ // Insert the new node before the current position to not affect
+ // iteration.
+ pending_.insertBefore(pm, lower);
+
+ // Overwrite pm in place for the upper move. Iteration proceeds as normal.
+ MoveOperand fromUpper = SplitIntoUpperHalf(pm->from());
+ MoveOperand toUpper = SplitIntoUpperHalf(pm->to());
+ pm->overwrite(fromUpper, toUpper, MoveOp::FLOAT32);
+ }
+ }
+#endif
+
+ InlineList<PendingMove> stack;
+
+ // This is a depth-first-search without recursion, which tries to find
+ // cycles in a list of moves.
+ //
+ // Algorithm.
+ //
+ // S = Traversal stack.
+ // P = Pending move list.
+ // O = Ordered list of moves.
+ //
+ // As long as there are pending moves in P:
+ // Let |root| be any pending move removed from P
+ // Add |root| to the traversal stack.
+ // As long as S is not empty:
+ // Let |L| be the most recent move added to S.
+ //
+ // Find any pending move M whose source is L's destination, thus
+ // preventing L's move until M has completed.
+ //
+ // If a move M was found,
+ // Remove M from the pending list.
+ // If M's destination is |root|,
+ // Annotate M and |root| as cycles.
+ // Add M to S.
+ // do not Add M to O, since M may have other conflictors in P
+ // that have not yet been processed.
+ // Otherwise,
+ // Add M to S.
+ // Otherwise,
+ // Remove L from S.
+ // Add L to O.
+ //
+ while (!pending_.empty()) {
+ PendingMove* pm = pending_.popBack();
+
+ // Add this pending move to the cycle detection stack.
+ stack.pushBack(pm);
+
+ while (!stack.empty()) {
+ PendingMove* blocking = findBlockingMove(stack.peekBack());
+
+ if (blocking) {
+ PendingMoveIterator stackiter = stack.begin();
+ PendingMove* cycled = findCycledMove(&stackiter, stack.end(), blocking);
+ if (cycled) {
+ // Find the cycle's start.
+ // We annotate cycles at each move in the cycle, and
+ // assert that we do not find two cycles in one move chain
+ // traversal (which would indicate two moves to the same
+ // destination).
+ // Since there can be more than one cycle, find them all.
+ do {
+ cycled->setCycleEnd(curCycles_);
+ cycled = findCycledMove(&stackiter, stack.end(), blocking);
+ } while (cycled);
+
+ blocking->setCycleBegin(pm->type(), curCycles_);
+ curCycles_++;
+ pending_.remove(blocking);
+ stack.pushBack(blocking);
+ } else {
+ // This is a new link in the move chain, so keep
+ // searching for a cycle.
+ pending_.remove(blocking);
+ stack.pushBack(blocking);
+ }
+ } else {
+ // Otherwise, pop the last move on the search stack because it's
+ // complete and not participating in a cycle. The resulting
+ // move can safely be added to the ordered move list.
+ PendingMove* done = stack.popBack();
+ if (!addOrderedMove(*done)) {
+ return false;
+ }
+ movePool_.free(done);
+ }
+ }
+ // If the current queue is empty, it is certain that there are
+ // all previous cycles cannot conflict with future cycles,
+ // so re-set the counter of pending cycles, while keeping a high-water mark.
+ if (numCycles_ < curCycles_) {
+ numCycles_ = curCycles_;
+ }
+ curCycles_ = 0;
+ }
+
+ return true;
+}
+
+bool MoveResolver::addOrderedMove(const MoveOp& move) {
+ // Sometimes the register allocator generates move groups where multiple
+ // moves have the same source. Try to optimize these cases when the source
+ // is in memory and the target of one of the moves is in a register.
+ MOZ_ASSERT(!move.from().aliases(move.to()));
+
+ if (!move.from().isMemory() || move.isCycleBegin() || move.isCycleEnd()) {
+ return orderedMoves_.append(move);
+ }
+
+ // Look for an earlier move with the same source, where no intervening move
+ // touches either the source or destination of the new move.
+ for (int i = orderedMoves_.length() - 1; i >= 0; i--) {
+ const MoveOp& existing = orderedMoves_[i];
+
+ if (existing.from() == move.from() && !existing.to().aliases(move.to()) &&
+ existing.type() == move.type() && !existing.isCycleBegin() &&
+ !existing.isCycleEnd()) {
+ MoveOp* after = orderedMoves_.begin() + i + 1;
+ if (existing.to().isGeneralReg() || existing.to().isFloatReg()) {
+ MoveOp nmove(existing.to(), move.to(), move.type());
+ return orderedMoves_.insert(after, nmove);
+ } else if (move.to().isGeneralReg() || move.to().isFloatReg()) {
+ MoveOp nmove(move.to(), existing.to(), move.type());
+ orderedMoves_[i] = move;
+ return orderedMoves_.insert(after, nmove);
+ }
+ }
+
+ if (existing.aliases(move)) {
+ break;
+ }
+ }
+
+ return orderedMoves_.append(move);
+}
+
+void MoveResolver::reorderMove(size_t from, size_t to) {
+ MOZ_ASSERT(from != to);
+
+ MoveOp op = orderedMoves_[from];
+ if (from < to) {
+ for (size_t i = from; i < to; i++) {
+ orderedMoves_[i] = orderedMoves_[i + 1];
+ }
+ } else {
+ for (size_t i = from; i > to; i--) {
+ orderedMoves_[i] = orderedMoves_[i - 1];
+ }
+ }
+ orderedMoves_[to] = op;
+}
+
+void MoveResolver::sortMemoryToMemoryMoves() {
+ // Try to reorder memory->memory moves so that they are executed right
+ // before a move that clobbers some register. This will allow the move
+ // emitter to use that clobbered register as a scratch register for the
+ // memory->memory move, if necessary.
+ for (size_t i = 0; i < orderedMoves_.length(); i++) {
+ const MoveOp& base = orderedMoves_[i];
+ if (!base.from().isMemory() || !base.to().isMemory()) {
+ continue;
+ }
+ if (base.type() != MoveOp::GENERAL && base.type() != MoveOp::INT32) {
+ continue;
+ }
+
+ // Look for an earlier move clobbering a register.
+ bool found = false;
+ for (int j = i - 1; j >= 0; j--) {
+ const MoveOp& previous = orderedMoves_[j];
+ if (previous.aliases(base) || previous.isCycleBegin() ||
+ previous.isCycleEnd()) {
+ break;
+ }
+
+ if (previous.to().isGeneralReg()) {
+ reorderMove(i, j);
+ found = true;
+ break;
+ }
+ }
+ if (found) {
+ continue;
+ }
+
+ // Look for a later move clobbering a register.
+ if (i + 1 < orderedMoves_.length()) {
+ bool found = false, skippedRegisterUse = false;
+ for (size_t j = i + 1; j < orderedMoves_.length(); j++) {
+ const MoveOp& later = orderedMoves_[j];
+ if (later.aliases(base) || later.isCycleBegin() || later.isCycleEnd()) {
+ break;
+ }
+
+ if (later.to().isGeneralReg()) {
+ if (skippedRegisterUse) {
+ reorderMove(i, j);
+ found = true;
+ } else {
+ // There is no move that uses a register between the
+ // original memory->memory move and this move that
+ // clobbers a register. The move should already be able
+ // to use a scratch register, so don't shift anything
+ // around.
+ }
+ break;
+ }
+
+ if (later.from().isGeneralReg()) {
+ skippedRegisterUse = true;
+ }
+ }
+
+ if (found) {
+ // Redo the search for memory->memory moves at the current
+ // index, so we don't skip the move just shifted back.
+ i--;
+ }
+ }
+ }
+}
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