Allow the register scavenger to spill multiple registers

This patch lets the register scavenger make use of multiple spill slots in
order to guarantee that it will be able to provide multiple registers
simultaneously.

To support this, the RS's API has changed slightly: setScavengingFrameIndex /
getScavengingFrameIndex have been replaced by addScavengingFrameIndex /
isScavengingFrameIndex / getScavengingFrameIndices.

In forthcoming commits, the PowerPC backend will use this capability in order
to implement the spilling of condition registers, and some special-purpose
registers, without relying on r0 being reserved. In some cases, spilling these
registers requires two GPRs: one for addressing and one to hold the value being
transferred.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177774 91177308-0d34-0410-b5e6-96231b3b80d8

10 files changed, 84 insertions, 43 deletions

diff --git a/include/llvm/CodeGen/RegisterScavenging.h b/include/llvm/CodeGen/RegisterScavenging.h
index a2b1533e5d..babb96b962 100644
--- a/include/llvm/CodeGen/RegisterScavenging.h
+++ b/include/llvm/CodeGen/RegisterScavenging.h
@@ -40,17 +40,23 @@ class RegScavenger {
   /// registers.
   bool Tracking;
 
-  /// ScavengingFrameIndex - Special spill slot used for scavenging a register
-  /// post register allocation.
-  int ScavengingFrameIndex;
+  /// Information on scavenged registers (held in a spill slot).
+  struct ScavengedInfo {
+    ScavengedInfo(int FI) : FrameIndex(FI), Reg(0), Restore(NULL) {}
 
-  /// ScavengedReg - If none zero, the specific register is currently being
-  /// scavenged. That is, it is spilled to the special scavenging stack slot.
-  unsigned ScavengedReg;
+    /// A spill slot used for scavenging a register post register allocation.
+    int FrameIndex;
 
-  /// ScavengeRestore - Instruction that restores the scavenged register from
-  /// stack.
-  const MachineInstr *ScavengeRestore;
+    /// If non-zero, the specific register is currently being
+    /// scavenged. That is, it is spilled to this scavenging stack slot.
+    unsigned Reg;
+
+    /// The instruction that restores the scavenged register from stack.
+    const MachineInstr *Restore;
+  };
+
+  /// A vector of information on scavenged registers.
+  SmallVector<ScavengedInfo, 2> Scavenged;
 
   /// CalleeSavedrRegs - A bitvector of callee saved registers for the target.
   ///
@@ -67,8 +73,7 @@ class RegScavenger {
 
 public:
   RegScavenger()
-    : MBB(NULL), NumPhysRegs(0), Tracking(false),
-      ScavengingFrameIndex(-1), ScavengedReg(0) {}
+    : MBB(NULL), NumPhysRegs(0), Tracking(false) {}
 
   /// enterBasicBlock - Start tracking liveness from the begin of the specific
   /// basic block.
@@ -103,10 +108,27 @@ public:
   /// Return 0 if none is found.
   unsigned FindUnusedReg(const TargetRegisterClass *RegClass) const;
 
-  /// setScavengingFrameIndex / getScavengingFrameIndex - accessor and setter of
-  /// ScavengingFrameIndex.
-  void setScavengingFrameIndex(int FI) { ScavengingFrameIndex = FI; }
-  int getScavengingFrameIndex() const { return ScavengingFrameIndex; }
+  /// Add a scavenging frame index.
+  void addScavengingFrameIndex(int FI) {
+    Scavenged.push_back(ScavengedInfo(FI));
+  }
+
+  /// Query whether a frame index is a scavenging frame index.
+  bool isScavengingFrameIndex(int FI) const {
+    for (SmallVector<ScavengedInfo, 2>::const_iterator I = Scavenged.begin(),
+         IE = Scavenged.end(); I != IE; ++I)
+      if (I->FrameIndex == FI)
+        return true;
+
+    return false;
+  }
+
+  /// Get an array of scavenging frame indices.
+  void getScavengingFrameIndices(SmallVectorImpl<int> &A) const {
+    for (SmallVector<ScavengedInfo, 2>::const_iterator I = Scavenged.begin(),
+         IE = Scavenged.end(); I != IE; ++I)
+      A.push_back(I->FrameIndex);
+  }
 
   /// scavengeRegister - Make a register of the specific register class
   /// available and do the appropriate bookkeeping. SPAdj is the stack
diff --git a/lib/CodeGen/PrologEpilogInserter.cpp b/lib/CodeGen/PrologEpilogInserter.cpp
index 855a8c5f92..413ce91ead 100644
--- a/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/lib/CodeGen/PrologEpilogInserter.cpp
@@ -548,9 +548,11 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
   const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
   if (RS && TFI.hasFP(Fn) && RegInfo->useFPForScavengingIndex(Fn) &&
       !RegInfo->needsStackRealignment(Fn)) {
-    int SFI = RS->getScavengingFrameIndex();
-    if (SFI >= 0)
-      AdjustStackOffset(MFI, SFI, StackGrowsDown, Offset, MaxAlign);
+    SmallVector<int, 2> SFIs;
+    RS->getScavengingFrameIndices(SFIs);
+    for (SmallVector<int, 2>::iterator I = SFIs.begin(),
+         IE = SFIs.end(); I != IE; ++I)
+      AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign);
   }
 
   // FIXME: Once this is working, then enable flag will change to a target
@@ -593,7 +595,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
         continue;
       if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
         continue;
-      if (RS && (int)i == RS->getScavengingFrameIndex())
+      if (RS && RS->isScavengingFrameIndex((int)i))
         continue;
       if (MFI->isDeadObjectIndex(i))
         continue;
@@ -615,7 +617,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
       continue;
     if (i >= MinCSFrameIndex && i <= MaxCSFrameIndex)
       continue;
-    if (RS && (int)i == RS->getScavengingFrameIndex())
+    if (RS && RS->isScavengingFrameIndex((int)i))
       continue;
     if (MFI->isDeadObjectIndex(i))
       continue;
@@ -631,9 +633,11 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
   // stack pointer.
   if (RS && (!TFI.hasFP(Fn) || RegInfo->needsStackRealignment(Fn) ||
              !RegInfo->useFPForScavengingIndex(Fn))) {
-    int SFI = RS->getScavengingFrameIndex();
-    if (SFI >= 0)
-      AdjustStackOffset(MFI, SFI, StackGrowsDown, Offset, MaxAlign);
+    SmallVector<int, 2> SFIs;
+    RS->getScavengingFrameIndices(SFIs);
+    for (SmallVector<int, 2>::iterator I = SFIs.begin(),
+         IE = SFIs.end(); I != IE; ++I)
+      AdjustStackOffset(MFI, *I, StackGrowsDown, Offset, MaxAlign);
   }
 
   if (!TFI.targetHandlesStackFrameRounding()) {
diff --git a/lib/CodeGen/RegisterScavenging.cpp b/lib/CodeGen/RegisterScavenging.cpp
index d0d30e8f94..be33854060 100644
--- a/lib/CodeGen/RegisterScavenging.cpp
+++ b/lib/CodeGen/RegisterScavenging.cpp
@@ -45,8 +45,11 @@ bool RegScavenger::isAliasUsed(unsigned Reg) const {
 }
 
 void RegScavenger::initRegState() {
-  ScavengedReg = 0;
-  ScavengeRestore = NULL;
+  for (SmallVector<ScavengedInfo, 2>::iterator I = Scavenged.begin(),
+       IE = Scavenged.end(); I != IE; ++I) {
+    I->Reg = 0;
+    I->Restore = NULL;
+  }
 
   // All registers started out unused.
   RegsAvailable.set();
@@ -120,9 +123,13 @@ void RegScavenger::forward() {
 
   MachineInstr *MI = MBBI;
 
-  if (MI == ScavengeRestore) {
-    ScavengedReg = 0;
-    ScavengeRestore = NULL;
+  for (SmallVector<ScavengedInfo, 2>::iterator I = Scavenged.begin(),
+       IE = Scavenged.end(); I != IE; ++I) {
+    if (I->Restore != MI)
+      continue;
+
+    I->Reg = 0;
+    I->Restore = NULL;
   }
 
   if (MI->isDebugValue())
@@ -358,36 +365,44 @@ unsigned RegScavenger::scavengeRegister(const TargetRegisterClass *RC,
     return SReg;
   }
 
-  assert(ScavengedReg == 0 &&
-         "Scavenger slot is live, unable to scavenge another register!");
+  // Find an available scavenging slot.
+  int SI;
+  for (SI = 0; SI < Scavenged.size(); ++SI)
+    if (Scavenged[SI].Reg == 0)
+      break;
+
+  assert(SI < Scavenged.size() &&
+         "Scavenger slots are live, unable to scavenge another register!");
 
   // Avoid infinite regress
-  ScavengedReg = SReg;
+  Scavenged[SI].Reg = SReg;
 
   // If the target knows how to save/restore the register, let it do so;
   // otherwise, use the emergency stack spill slot.
   if (!TRI->saveScavengerRegister(*MBB, I, UseMI, RC, SReg)) {
     // Spill the scavenged register before I.
-    assert(ScavengingFrameIndex >= 0 &&
+    assert(Scavenged[SI].FrameIndex >= 0 &&
            "Cannot scavenge register without an emergency spill slot!");
-    TII->storeRegToStackSlot(*MBB, I, SReg, true, ScavengingFrameIndex, RC,TRI);
+    TII->storeRegToStackSlot(*MBB, I, SReg, true, Scavenged[SI].FrameIndex,
+                             RC, TRI);
     MachineBasicBlock::iterator II = prior(I);
 
     unsigned FIOperandNum = getFrameIndexOperandNum(II);
     TRI->eliminateFrameIndex(II, SPAdj, FIOperandNum, this);
 
     // Restore the scavenged register before its use (or first terminator).
-    TII->loadRegFromStackSlot(*MBB, UseMI, SReg, ScavengingFrameIndex, RC, TRI);
+    TII->loadRegFromStackSlot(*MBB, UseMI, SReg, Scavenged[SI].FrameIndex,
+                              RC, TRI);
     II = prior(UseMI);
 
     FIOperandNum = getFrameIndexOperandNum(II);
     TRI->eliminateFrameIndex(II, SPAdj, FIOperandNum, this);
   }
 
-  ScavengeRestore = prior(UseMI);
+  Scavenged[SI].Restore = prior(UseMI);
 
   // Doing this here leads to infinite regress.
-  // ScavengedReg = SReg;
+  // Scavenged[SI].Reg = SReg;
 
   DEBUG(dbgs() << "Scavenged register (with spill): " << TRI->getName(SReg) <<
         "\n");
diff --git a/lib/Target/AArch64/AArch64FrameLowering.cpp b/lib/Target/AArch64/AArch64FrameLowering.cpp
index 572617cc07..dc41f2f605 100644
--- a/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/lib/Target/AArch64/AArch64FrameLowering.cpp
@@ -396,7 +396,7 @@ AArch64FrameLowering::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
     // helpfully places it near either SP or FP for us to avoid
     // infinitely-regression during scavenging.
     const TargetRegisterClass *RC = &AArch64::GPR64RegClass;
-    RS->setScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
+    RS->addScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
                                                        RC->getAlignment(),
                                                        false));
   }
diff --git a/lib/Target/ARM/ARMBaseRegisterInfo.cpp b/lib/Target/ARM/ARMBaseRegisterInfo.cpp
index abdd251743..b6b27f849a 100644
--- a/lib/Target/ARM/ARMBaseRegisterInfo.cpp
+++ b/lib/Target/ARM/ARMBaseRegisterInfo.cpp
@@ -680,7 +680,7 @@ ARMBaseRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   // means the stack pointer cannot be used to access the emergency spill slot
   // when !hasReservedCallFrame().
 #ifndef NDEBUG
-  if (RS && FrameReg == ARM::SP && FrameIndex == RS->getScavengingFrameIndex()){
+  if (RS && FrameReg == ARM::SP && RS->isScavengingFrameIndex(FrameIndex)){
     assert(TFI->hasReservedCallFrame(MF) &&
            "Cannot use SP to access the emergency spill slot in "
            "functions without a reserved call frame");
diff --git a/lib/Target/ARM/ARMFrameLowering.cpp b/lib/Target/ARM/ARMFrameLowering.cpp
index 3b12408768..7a02adf246 100644
--- a/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/lib/Target/ARM/ARMFrameLowering.cpp
@@ -1368,7 +1368,7 @@ ARMFrameLowering::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
         // note: Thumb1 functions spill to R12, not the stack.  Reserve a slot
         // closest to SP or frame pointer.
         const TargetRegisterClass *RC = &ARM::GPRRegClass;
-        RS->setScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
+        RS->addScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
                                                            RC->getAlignment(),
                                                            false));
       }
diff --git a/lib/Target/ARM/Thumb1RegisterInfo.cpp b/lib/Target/ARM/Thumb1RegisterInfo.cpp
index 609d502aa5..7452fb776e 100644
--- a/lib/Target/ARM/Thumb1RegisterInfo.cpp
+++ b/lib/Target/ARM/Thumb1RegisterInfo.cpp
@@ -588,7 +588,7 @@ Thumb1RegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator II,
   // means the stack pointer cannot be used to access the emergency spill slot
   // when !hasReservedCallFrame().
 #ifndef NDEBUG
-  if (RS && FrameReg == ARM::SP && FrameIndex == RS->getScavengingFrameIndex()){
+  if (RS && FrameReg == ARM::SP && RS->isScavengingFrameIndex(FrameIndex)){
     assert(MF.getTarget().getFrameLowering()->hasReservedCallFrame(MF) &&
            "Cannot use SP to access the emergency spill slot in "
            "functions without a reserved call frame");
diff --git a/lib/Target/Mips/MipsSEFrameLowering.cpp b/lib/Target/Mips/MipsSEFrameLowering.cpp
index 0dd671376f..c67e1adef6 100644
--- a/lib/Target/Mips/MipsSEFrameLowering.cpp
+++ b/lib/Target/Mips/MipsSEFrameLowering.cpp
@@ -295,7 +295,7 @@ processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
     &Mips::CPU64RegsRegClass : &Mips::CPURegsRegClass;
   int FI = MF.getFrameInfo()->CreateStackObject(RC->getSize(),
                                                 RC->getAlignment(), false);
-  RS->setScavengingFrameIndex(FI);
+  RS->addScavengingFrameIndex(FI);
 }
 
 const MipsFrameLowering *
diff --git a/lib/Target/PowerPC/PPCFrameLowering.cpp b/lib/Target/PowerPC/PPCFrameLowering.cpp
index 0108f7256e..707c2a5d26 100644
--- a/lib/Target/PowerPC/PPCFrameLowering.cpp
+++ b/lib/Target/PowerPC/PPCFrameLowering.cpp
@@ -1086,7 +1086,7 @@ PPCFrameLowering::addScavengingSpillSlot(MachineFunction &MF,
     const TargetRegisterClass *GPRC = &PPC::GPRCRegClass;
     const TargetRegisterClass *G8RC = &PPC::G8RCRegClass;
     const TargetRegisterClass *RC = Subtarget.isPPC64() ? G8RC : GPRC;
-    RS->setScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
+    RS->addScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
                                                        RC->getAlignment(),
                                                        false));
   }
diff --git a/lib/Target/XCore/XCoreFrameLowering.cpp b/lib/Target/XCore/XCoreFrameLowering.cpp
index 019c4570d9..6b6480e4b4 100644
--- a/lib/Target/XCore/XCoreFrameLowering.cpp
+++ b/lib/Target/XCore/XCoreFrameLowering.cpp
@@ -409,7 +409,7 @@ XCoreFrameLowering::processFunctionBeforeCalleeSavedScan(MachineFunction &MF,
   }
   if (RegInfo->requiresRegisterScavenging(MF)) {
     // Reserve a slot close to SP or frame pointer.
-    RS->setScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
+    RS->addScavengingFrameIndex(MFI->CreateStackObject(RC->getSize(),
                                                        RC->getAlignment(),
                                                        false));
   }