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getScavengingFrameIndex have been replaced by addScavengingFrameIndex /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.

llvm-svn: 177774

9 files changed, 47 insertions, 28 deletions

diff --git a/llvm/lib/CodeGen/PrologEpilogInserter.cpp b/llvm/lib/CodeGen/PrologEpilogInserter.cpp
index 855a8c5f926..413ce91ead2 100644
--- a/llvm/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/llvm/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/llvm/lib/CodeGen/RegisterScavenging.cpp b/llvm/lib/CodeGen/RegisterScavenging.cpp
index d0d30e8f946..be338540600 100644
--- a/llvm/lib/CodeGen/RegisterScavenging.cpp
+++ b/llvm/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/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp b/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
index 572617cc078..dc41f2f6052 100644
--- a/llvm/lib/Target/AArch64/AArch64FrameLowering.cpp
+++ b/llvm/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/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp b/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
index abdd2517433..b6b27f849a2 100644
--- a/llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp
+++ b/llvm/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/llvm/lib/Target/ARM/ARMFrameLowering.cpp b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
index 3b124087683..7a02adf2463 100644
--- a/llvm/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/llvm/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/llvm/lib/Target/ARM/Thumb1RegisterInfo.cpp b/llvm/lib/Target/ARM/Thumb1RegisterInfo.cpp
index 609d502aa50..7452fb776eb 100644
--- a/llvm/lib/Target/ARM/Thumb1RegisterInfo.cpp
+++ b/llvm/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/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp b/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
index 0dd671376f8..c67e1adef60 100644
--- a/llvm/lib/Target/Mips/MipsSEFrameLowering.cpp
+++ b/llvm/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/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp b/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
index 0108f7256e2..707c2a5d263 100644
--- a/llvm/lib/Target/PowerPC/PPCFrameLowering.cpp
+++ b/llvm/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/llvm/lib/Target/XCore/XCoreFrameLowering.cpp b/llvm/lib/Target/XCore/XCoreFrameLowering.cpp
index 019c4570d93..6b6480e4b46 100644
--- a/llvm/lib/Target/XCore/XCoreFrameLowering.cpp
+++ b/llvm/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));
   }