6 files changed, 49 insertions, 1 deletions
diff --git a/docs/ReleaseNotes.html b/docs/ReleaseNotes.html
index 7dd0b8d550..011cbbd344 100644
--- a/docs/ReleaseNotes.html
+++ b/docs/ReleaseNotes.html
@@ -351,6 +351,10 @@ Release Notes</a>.</h1>
   represent combinations of constraints from instructions and sub-registers.
   The synthetic register classes inherit most of their properties form their
   closest user-defined super-class.</li>
+  <li><code>MachineRegisterInfo</code> now allows the reserved registers to be
+  frozen when register allocation starts.  Target hooks should use the
+  <code>MRI->canReserveReg(FramePtr)</code> method to avoid accidentally
+  disabling frame pointer elimination during register allocation.</li>
 </ul>
 </div>
 
diff --git a/include/llvm/CodeGen/MachineRegisterInfo.h b/include/llvm/CodeGen/MachineRegisterInfo.h
index 773683a748..34d454ebc9 100644
--- a/include/llvm/CodeGen/MachineRegisterInfo.h
+++ b/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -57,7 +57,13 @@ class MachineRegisterInfo {
   /// so that the code generator knows which callee save registers to save and
   /// for other target specific uses.
   BitVector UsedPhysRegs;
-  
+
+  /// ReservedRegs - This is a bit vector of reserved registers.  The target
+  /// may change its mind about which registers should be reserved.  This
+  /// vector is the frozen set of reserved registers when register allocation
+  /// started.
+  BitVector ReservedRegs;
+
   /// LiveIns/LiveOuts - Keep track of the physical registers that are
   /// livein/liveout of the function.  Live in values are typically arguments in
   /// registers, live out values are typically return values in registers.
@@ -309,6 +315,37 @@ public:
   /// subregisters. That means that if R is used, so are all subregisters.
   void closePhysRegsUsed(const TargetRegisterInfo&);
 
+
+  //===--------------------------------------------------------------------===//
+  // Reserved Register Info
+  //===--------------------------------------------------------------------===//
+  //
+  // The set of reserved registers must be invariant during register
+  // allocation.  For example, the target cannot suddenly decide it needs a
+  // frame pointer when the register allocator has already used the frame
+  // pointer register for something else.
+  //
+  // These methods can be used by target hooks like hasFP() to avoid changing
+  // the reserved register set during register allocation.
+
+  /// freezeReservedRegs - Called by the register allocator to freeze the set
+  /// of reserved registers before allocation begins.
+  void freezeReservedRegs(const MachineFunction&);
+
+  /// reservedRegsFrozen - Returns true after freezeReservedRegs() was called
+  /// to ensure the set of reserved registers stays constant.
+  bool reservedRegsFrozen() const {
+    return !ReservedRegs.empty();
+  }
+
+  /// canReserveReg - Returns true if PhysReg can be used as a reserved
+  /// register.  Any register can be reserved before freezeReservedRegs() is
+  /// called.
+  bool canReserveReg(unsigned PhysReg) const {
+    return !reservedRegsFrozen() || ReservedRegs.test(PhysReg);
+  }
+
+
   //===--------------------------------------------------------------------===//
   // LiveIn/LiveOut Management
   //===--------------------------------------------------------------------===//
diff --git a/lib/CodeGen/MachineRegisterInfo.cpp b/lib/CodeGen/MachineRegisterInfo.cpp
index c35b154aa1..67291a0eb8 100644
--- a/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/lib/CodeGen/MachineRegisterInfo.cpp
@@ -259,3 +259,7 @@ void MachineRegisterInfo::dumpUses(unsigned Reg) const {
     I.getOperand().getParent()->dump();
 }
 #endif
+
+void MachineRegisterInfo::freezeReservedRegs(const MachineFunction &MF) {
+  ReservedRegs = TRI->getReservedRegs(MF);
+}
diff --git a/lib/CodeGen/RegAllocBasic.cpp b/lib/CodeGen/RegAllocBasic.cpp
index 5496d69fd3..8019cf227b 100644
--- a/lib/CodeGen/RegAllocBasic.cpp
+++ b/lib/CodeGen/RegAllocBasic.cpp
@@ -233,6 +233,7 @@ void RegAllocBase::init(VirtRegMap &vrm, LiveIntervals &lis) {
   MRI = &vrm.getRegInfo();
   VRM = &vrm;
   LIS = &lis;
+  MRI->freezeReservedRegs(vrm.getMachineFunction());
   RegClassInfo.runOnMachineFunction(vrm.getMachineFunction());
 
   const unsigned NumRegs = TRI->getNumRegs();
diff --git a/lib/CodeGen/RegAllocFast.cpp b/lib/CodeGen/RegAllocFast.cpp
index c2656c5e5c..93f39b6c66 100644
--- a/lib/CodeGen/RegAllocFast.cpp
+++ b/lib/CodeGen/RegAllocFast.cpp
@@ -1047,6 +1047,7 @@ bool RAFast::runOnMachineFunction(MachineFunction &Fn) {
   TM = &Fn.getTarget();
   TRI = TM->getRegisterInfo();
   TII = TM->getInstrInfo();
+  MRI->freezeReservedRegs(Fn);
   RegClassInfo.runOnMachineFunction(Fn);
   UsedInInstr.resize(TRI->getNumRegs());
 
diff --git a/lib/CodeGen/RegAllocPBQP.cpp b/lib/CodeGen/RegAllocPBQP.cpp
index a053cccc9e..f8b0b9fa6e 100644
--- a/lib/CodeGen/RegAllocPBQP.cpp
+++ b/lib/CodeGen/RegAllocPBQP.cpp
@@ -619,6 +619,7 @@ bool RegAllocPBQP::runOnMachineFunction(MachineFunction &MF) {
   vrm = &getAnalysis<VirtRegMap>();
   spiller.reset(createInlineSpiller(*this, MF, *vrm));
 
+  mri->freezeReservedRegs(MF);
 
   DEBUG(dbgs() << "PBQP Register Allocating for " << mf->getFunction()->getName() << "\n");