1 files changed, 434 insertions, 0 deletions
diff --git a/js/src/jit/StupidAllocator.cpp b/js/src/jit/StupidAllocator.cpp
new file mode 100644
index 000000000..8e3ea6286
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+++ b/js/src/jit/StupidAllocator.cpp
@@ -0,0 +1,434 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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/StupidAllocator.h"
+
+#include "jstypes.h"
+
+using namespace js;
+using namespace js::jit;
+
+static inline uint32_t
+DefaultStackSlot(uint32_t vreg)
+{
+    // On x86/x64, we have to keep the stack aligned on 16 bytes for spilling
+    // SIMD registers.  To avoid complexity in this stupid allocator, we just
+    // allocate 16 bytes stack slot for all vreg.
+    return vreg * 2 * sizeof(Value);
+}
+
+LAllocation*
+StupidAllocator::stackLocation(uint32_t vreg)
+{
+    LDefinition* def = virtualRegisters[vreg];
+    if (def->policy() == LDefinition::FIXED && def->output()->isArgument())
+        return def->output();
+
+    return new(alloc()) LStackSlot(DefaultStackSlot(vreg));
+}
+
+StupidAllocator::RegisterIndex
+StupidAllocator::registerIndex(AnyRegister reg)
+{
+    for (size_t i = 0; i < registerCount; i++) {
+        if (reg == registers[i].reg)
+            return i;
+    }
+    MOZ_CRASH("Bad register");
+}
+
+bool
+StupidAllocator::init()
+{
+    if (!RegisterAllocator::init())
+        return false;
+
+    if (!virtualRegisters.appendN((LDefinition*)nullptr, graph.numVirtualRegisters()))
+        return false;
+
+    for (size_t i = 0; i < graph.numBlocks(); i++) {
+        LBlock* block = graph.getBlock(i);
+        for (LInstructionIterator ins = block->begin(); ins != block->end(); ins++) {
+            for (size_t j = 0; j < ins->numDefs(); j++) {
+                LDefinition* def = ins->getDef(j);
+                virtualRegisters[def->virtualRegister()] = def;
+            }
+
+            for (size_t j = 0; j < ins->numTemps(); j++) {
+                LDefinition* def = ins->getTemp(j);
+                if (def->isBogusTemp())
+                    continue;
+                virtualRegisters[def->virtualRegister()] = def;
+            }
+        }
+        for (size_t j = 0; j < block->numPhis(); j++) {
+            LPhi* phi = block->getPhi(j);
+            LDefinition* def = phi->getDef(0);
+            uint32_t vreg = def->virtualRegister();
+
+            virtualRegisters[vreg] = def;
+        }
+    }
+
+    // Assign physical registers to the tracked allocation.
+    {
+        registerCount = 0;
+        LiveRegisterSet remainingRegisters(allRegisters_.asLiveSet());
+        while (!remainingRegisters.emptyGeneral())
+            registers[registerCount++].reg = AnyRegister(remainingRegisters.takeAnyGeneral());
+
+        while (!remainingRegisters.emptyFloat())
+            registers[registerCount++].reg = AnyRegister(remainingRegisters.takeAnyFloat());
+
+        MOZ_ASSERT(registerCount <= MAX_REGISTERS);
+    }
+
+    return true;
+}
+
+bool
+StupidAllocator::allocationRequiresRegister(const LAllocation* alloc, AnyRegister reg)
+{
+    if (alloc->isRegister() && alloc->toRegister() == reg)
+        return true;
+    if (alloc->isUse()) {
+        const LUse* use = alloc->toUse();
+        if (use->policy() == LUse::FIXED) {
+            AnyRegister usedReg = GetFixedRegister(virtualRegisters[use->virtualRegister()], use);
+            if (usedReg.aliases(reg))
+                return true;
+        }
+    }
+    return false;
+}
+
+bool
+StupidAllocator::registerIsReserved(LInstruction* ins, AnyRegister reg)
+{
+    // Whether reg is already reserved for an input or output of ins.
+    for (LInstruction::InputIterator alloc(*ins); alloc.more(); alloc.next()) {
+        if (allocationRequiresRegister(*alloc, reg))
+            return true;
+    }
+    for (size_t i = 0; i < ins->numTemps(); i++) {
+        if (allocationRequiresRegister(ins->getTemp(i)->output(), reg))
+            return true;
+    }
+    for (size_t i = 0; i < ins->numDefs(); i++) {
+        if (allocationRequiresRegister(ins->getDef(i)->output(), reg))
+            return true;
+    }
+    return false;
+}
+
+AnyRegister
+StupidAllocator::ensureHasRegister(LInstruction* ins, uint32_t vreg)
+{
+    // Ensure that vreg is held in a register before ins.
+
+    // Check if the virtual register is already held in a physical register.
+    RegisterIndex existing = findExistingRegister(vreg);
+    if (existing != UINT32_MAX) {
+        if (registerIsReserved(ins, registers[existing].reg)) {
+            evictAliasedRegister(ins, existing);
+        } else {
+            registers[existing].age = ins->id();
+            return registers[existing].reg;
+        }
+    }
+
+    RegisterIndex best = allocateRegister(ins, vreg);
+    loadRegister(ins, vreg, best, virtualRegisters[vreg]->type());
+
+    return registers[best].reg;
+}
+
+StupidAllocator::RegisterIndex
+StupidAllocator::allocateRegister(LInstruction* ins, uint32_t vreg)
+{
+    // Pick a register for vreg, evicting an existing register if necessary.
+    // Spill code will be placed before ins, and no existing allocated input
+    // for ins will be touched.
+    MOZ_ASSERT(ins);
+
+    LDefinition* def = virtualRegisters[vreg];
+    MOZ_ASSERT(def);
+
+    RegisterIndex best = UINT32_MAX;
+
+    for (size_t i = 0; i < registerCount; i++) {
+        AnyRegister reg = registers[i].reg;
+
+        if (!def->isCompatibleReg(reg))
+            continue;
+
+        // Skip the register if it is in use for an allocated input or output.
+        if (registerIsReserved(ins, reg))
+            continue;
+
+        if (registers[i].vreg == MISSING_ALLOCATION ||
+            best == UINT32_MAX ||
+            registers[best].age > registers[i].age)
+        {
+            best = i;
+        }
+    }
+
+    evictAliasedRegister(ins, best);
+    return best;
+}
+
+void
+StupidAllocator::syncRegister(LInstruction* ins, RegisterIndex index)
+{
+    if (registers[index].dirty) {
+        LMoveGroup* input = getInputMoveGroup(ins);
+        LAllocation source(registers[index].reg);
+
+        uint32_t existing = registers[index].vreg;
+        LAllocation* dest = stackLocation(existing);
+        input->addAfter(source, *dest, registers[index].type);
+
+        registers[index].dirty = false;
+    }
+}
+
+void
+StupidAllocator::evictRegister(LInstruction* ins, RegisterIndex index)
+{
+    syncRegister(ins, index);
+    registers[index].set(MISSING_ALLOCATION);
+}
+
+void
+StupidAllocator::evictAliasedRegister(LInstruction* ins, RegisterIndex index)
+{
+    for (size_t i = 0; i < registers[index].reg.numAliased(); i++) {
+        uint32_t aindex = registerIndex(registers[index].reg.aliased(i));
+        syncRegister(ins, aindex);
+        registers[aindex].set(MISSING_ALLOCATION);
+    }
+}
+
+void
+StupidAllocator::loadRegister(LInstruction* ins, uint32_t vreg, RegisterIndex index, LDefinition::Type type)
+{
+    // Load a vreg from its stack location to a register.
+    LMoveGroup* input = getInputMoveGroup(ins);
+    LAllocation* source = stackLocation(vreg);
+    LAllocation dest(registers[index].reg);
+    input->addAfter(*source, dest, type);
+    registers[index].set(vreg, ins);
+    registers[index].type = type;
+}
+
+StupidAllocator::RegisterIndex
+StupidAllocator::findExistingRegister(uint32_t vreg)
+{
+    for (size_t i = 0; i < registerCount; i++) {
+        if (registers[i].vreg == vreg)
+            return i;
+    }
+    return UINT32_MAX;
+}
+
+bool
+StupidAllocator::go()
+{
+    // This register allocator is intended to be as simple as possible, while
+    // still being complicated enough to share properties with more complicated
+    // allocators. Namely, physical registers may be used to carry virtual
+    // registers across LIR instructions, but not across basic blocks.
+    //
+    // This algorithm does not pay any attention to liveness. It is performed
+    // as a single forward pass through the basic blocks in the program. As
+    // virtual registers and temporaries are defined they are assigned physical
+    // registers, evicting existing allocations in an LRU fashion.
+
+    // For virtual registers not carried in a register, a canonical spill
+    // location is used. Each vreg has a different spill location; since we do
+    // not track liveness we cannot determine that two vregs have disjoint
+    // lifetimes. Thus, the maximum stack height is the number of vregs (scaled
+    // by two on 32 bit platforms to allow storing double values).
+    graph.setLocalSlotCount(DefaultStackSlot(graph.numVirtualRegisters()));
+
+    if (!init())
+        return false;
+
+    for (size_t blockIndex = 0; blockIndex < graph.numBlocks(); blockIndex++) {
+        LBlock* block = graph.getBlock(blockIndex);
+        MOZ_ASSERT(block->mir()->id() == blockIndex);
+
+        for (size_t i = 0; i < registerCount; i++)
+            registers[i].set(MISSING_ALLOCATION);
+
+        for (LInstructionIterator iter = block->begin(); iter != block->end(); iter++) {
+            LInstruction* ins = *iter;
+
+            if (ins == *block->rbegin())
+                syncForBlockEnd(block, ins);
+
+            allocateForInstruction(ins);
+        }
+    }
+
+    return true;
+}
+
+void
+StupidAllocator::syncForBlockEnd(LBlock* block, LInstruction* ins)
+{
+    // Sync any dirty registers, and update the synced state for phi nodes at
+    // each successor of a block. We cannot conflate the storage for phis with
+    // that of their inputs, as we cannot prove the live ranges of the phi and
+    // its input do not overlap. The values for the two may additionally be
+    // different, as the phi could be for the value of the input in a previous
+    // loop iteration.
+
+    for (size_t i = 0; i < registerCount; i++)
+        syncRegister(ins, i);
+
+    LMoveGroup* group = nullptr;
+
+    MBasicBlock* successor = block->mir()->successorWithPhis();
+    if (successor) {
+        uint32_t position = block->mir()->positionInPhiSuccessor();
+        LBlock* lirsuccessor = successor->lir();
+        for (size_t i = 0; i < lirsuccessor->numPhis(); i++) {
+            LPhi* phi = lirsuccessor->getPhi(i);
+
+            uint32_t sourcevreg = phi->getOperand(position)->toUse()->virtualRegister();
+            uint32_t destvreg = phi->getDef(0)->virtualRegister();
+
+            if (sourcevreg == destvreg)
+                continue;
+
+            LAllocation* source = stackLocation(sourcevreg);
+            LAllocation* dest = stackLocation(destvreg);
+
+            if (!group) {
+                // The moves we insert here need to happen simultaneously with
+                // each other, yet after any existing moves before the instruction.
+                LMoveGroup* input = getInputMoveGroup(ins);
+                if (input->numMoves() == 0) {
+                    group = input;
+                } else {
+                    group = LMoveGroup::New(alloc());
+                    block->insertAfter(input, group);
+                }
+            }
+
+            group->add(*source, *dest, phi->getDef(0)->type());
+        }
+    }
+}
+
+void
+StupidAllocator::allocateForInstruction(LInstruction* ins)
+{
+    // Sync all registers before making a call.
+    if (ins->isCall()) {
+        for (size_t i = 0; i < registerCount; i++)
+            syncRegister(ins, i);
+    }
+
+    // Allocate for inputs which are required to be in registers.
+    for (LInstruction::InputIterator alloc(*ins); alloc.more(); alloc.next()) {
+        if (!alloc->isUse())
+            continue;
+        LUse* use = alloc->toUse();
+        uint32_t vreg = use->virtualRegister();
+        if (use->policy() == LUse::REGISTER) {
+            AnyRegister reg = ensureHasRegister(ins, vreg);
+            alloc.replace(LAllocation(reg));
+        } else if (use->policy() == LUse::FIXED) {
+            AnyRegister reg = GetFixedRegister(virtualRegisters[vreg], use);
+            RegisterIndex index = registerIndex(reg);
+            if (registers[index].vreg != vreg) {
+                // Need to evict multiple registers
+                evictAliasedRegister(ins, registerIndex(reg));
+                // If this vreg is already assigned to an incorrect register
+                RegisterIndex existing = findExistingRegister(vreg);
+                if (existing != UINT32_MAX)
+                    evictRegister(ins, existing);
+                loadRegister(ins, vreg, index, virtualRegisters[vreg]->type());
+            }
+            alloc.replace(LAllocation(reg));
+        } else {
+            // Inputs which are not required to be in a register are not
+            // allocated until after temps/definitions, as the latter may need
+            // to evict registers which hold these inputs.
+        }
+    }
+
+    // Find registers to hold all temporaries and outputs of the instruction.
+    for (size_t i = 0; i < ins->numTemps(); i++) {
+        LDefinition* def = ins->getTemp(i);
+        if (!def->isBogusTemp())
+            allocateForDefinition(ins, def);
+    }
+    for (size_t i = 0; i < ins->numDefs(); i++) {
+        LDefinition* def = ins->getDef(i);
+        allocateForDefinition(ins, def);
+    }
+
+    // Allocate for remaining inputs which do not need to be in registers.
+    for (LInstruction::InputIterator alloc(*ins); alloc.more(); alloc.next()) {
+        if (!alloc->isUse())
+            continue;
+        LUse* use = alloc->toUse();
+        uint32_t vreg = use->virtualRegister();
+        MOZ_ASSERT(use->policy() != LUse::REGISTER && use->policy() != LUse::FIXED);
+
+        RegisterIndex index = findExistingRegister(vreg);
+        if (index == UINT32_MAX) {
+            LAllocation* stack = stackLocation(use->virtualRegister());
+            alloc.replace(*stack);
+        } else {
+            registers[index].age = ins->id();
+            alloc.replace(LAllocation(registers[index].reg));
+        }
+    }
+
+    // If this is a call, evict all registers except for those holding outputs.
+    if (ins->isCall()) {
+        for (size_t i = 0; i < registerCount; i++) {
+            if (!registers[i].dirty)
+                registers[i].set(MISSING_ALLOCATION);
+        }
+    }
+}
+
+void
+StupidAllocator::allocateForDefinition(LInstruction* ins, LDefinition* def)
+{
+    uint32_t vreg = def->virtualRegister();
+
+    CodePosition from;
+    if ((def->output()->isRegister() && def->policy() == LDefinition::FIXED) ||
+        def->policy() == LDefinition::MUST_REUSE_INPUT)
+    {
+        // Result will be in a specific register, spill any vreg held in
+        // that register before the instruction.
+        RegisterIndex index =
+            registerIndex(def->policy() == LDefinition::FIXED
+                          ? def->output()->toRegister()
+                          : ins->getOperand(def->getReusedInput())->toRegister());
+        evictRegister(ins, index);
+        registers[index].set(vreg, ins, true);
+        registers[index].type = virtualRegisters[vreg]->type();
+        def->setOutput(LAllocation(registers[index].reg));
+    } else if (def->policy() == LDefinition::FIXED) {
+        // The result must be a stack location.
+        def->setOutput(*stackLocation(vreg));
+    } else {
+        // Find a register to hold the result of the instruction.
+        RegisterIndex best = allocateRegister(ins, vreg);
+        registers[best].set(vreg, ins, true);
+        registers[best].type = virtualRegisters[vreg]->type();
+        def->setOutput(LAllocation(registers[best].reg));
+    }
+}