V4 JIT: calculate used registers and only save those.

Instead of saving all possibly used ones. Note that floating point
registers are not saved yet, as we don't support callee-saved FP
registers yet.

Change-Id: I1db2ba2513f7b466c64ec103eda0c464269247b0
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>

3 files changed, 37 insertions, 2 deletions

diff --git a/src/qml/jit/qv4isel_masm.cpp b/src/qml/jit/qv4isel_masm.cpp
index 5547190303..39e7c0fbc2 100644
--- a/src/qml/jit/qv4isel_masm.cpp
+++ b/src/qml/jit/qv4isel_masm.cpp
@@ -225,8 +225,9 @@ void InstructionSelection::run(int functionIndex)
 
     static const bool withRegisterAllocator = qgetenv("QV4_NO_REGALLOC").isEmpty();
     if (Assembler::RegAllocIsSupported && opt.isInSSA() && withRegisterAllocator) {
-        RegisterAllocator(Assembler::getRegisterInfo()).run(_function, opt);
-        calculateRegistersToSave(Assembler::getRegisterInfo());
+        RegisterAllocator regalloc(Assembler::getRegisterInfo());
+        regalloc.run(_function, opt);
+        calculateRegistersToSave(regalloc.usedRegisters());
     } else {
         if (opt.isInSSA())
             // No register allocator available for this platform, or env. var was set, so:
diff --git a/src/qml/jit/qv4regalloc.cpp b/src/qml/jit/qv4regalloc.cpp
index 0639c5361f..15a92770ca 100644
--- a/src/qml/jit/qv4regalloc.cpp
+++ b/src/qml/jit/qv4regalloc.cpp
@@ -1241,6 +1241,9 @@ RegisterAllocator::RegisterAllocator(const QV4::JIT::RegisterInformation &regist
     Q_ASSERT(_fpRegisters.size() >= 2);
     _active.reserve((_normalRegisters.size() + _fpRegisters.size()) * 2);
     _inactive.reserve(_active.size());
+
+    _regularRegsInUse.resize(_normalRegisters.size());
+    _fpRegsInUse.resize(_fpRegisters.size());
 }
 
 RegisterAllocator::~RegisterAllocator()
@@ -1303,6 +1306,31 @@ void RegisterAllocator::run(IR::Function *function, const Optimizer &opt)
     }
 }
 
+RegisterInformation RegisterAllocator::usedRegisters() const
+{
+    RegisterInformation regInfo;
+
+    for (int i = 0, ei = _normalRegisters.size(); i != ei; ++i) {
+        if (_regularRegsInUse.testBit(i))
+            regInfo.append(*_normalRegisters.at(i));
+    }
+
+    for (int i = 0, ei = _fpRegisters.size(); i != ei; ++i) {
+        if (_fpRegsInUse.testBit(i))
+            regInfo.append(*_fpRegisters.at(i));
+    }
+
+    return regInfo;
+}
+
+void RegisterAllocator::markInUse(int reg, bool isFPReg)
+{
+    if (isFPReg)
+        _fpRegsInUse.setBit(reg);
+    else
+        _regularRegsInUse.setBit(reg);
+}
+
 static inline LifeTimeInterval createFixedInterval(int rangeCount)
 {
     LifeTimeInterval i(rangeCount);
@@ -1565,6 +1593,7 @@ void RegisterAllocator::tryAllocateFreeReg(LifeTimeInterval &current)
             qDebug() << "*** allocating register" << reg << "for the whole interval of %" << current.temp().index;
         current.setReg(reg);
         _lastAssignedRegister[current.temp().index] = reg;
+        markInUse(reg, needsFPReg);
     } else {
         // register available for the first part of the interval
 
@@ -1580,6 +1609,7 @@ void RegisterAllocator::tryAllocateFreeReg(LifeTimeInterval &current)
         if (DebugRegAlloc)
             qDebug() << "*** allocating register" << reg << "for the first part of interval of %" << current.temp().index;
         split(current, freeUntilPos_reg, true);
+        markInUse(reg, needsFPReg);
     }
 }
 
diff --git a/src/qml/jit/qv4regalloc_p.h b/src/qml/jit/qv4regalloc_p.h
index 34ae19dfec..e1f075cb07 100644
--- a/src/qml/jit/qv4regalloc_p.h
+++ b/src/qml/jit/qv4regalloc_p.h
@@ -93,6 +93,8 @@ class RegisterAllocator
     std::vector<int> _assignedSpillSlots;
     QVector<int> _activeSpillSlots;
 
+    QBitArray _regularRegsInUse, _fpRegsInUse;
+
     Q_DISABLE_COPY(RegisterAllocator)
 
 public:
@@ -102,8 +104,10 @@ public:
     ~RegisterAllocator();
 
     void run(IR::Function *function, const IR::Optimizer &opt);
+    RegisterInformation usedRegisters() const;
 
 private:
+    void markInUse(int reg, bool isFPReg);
     LifeTimeInterval *cloneFixedInterval(int reg, bool isFP, const LifeTimeInterval &original);
     void prepareRanges();
     void linearScan();