[SystemZ] Clean up register scavenging code

SystemZ wants normal register scavenging slots, as close to the stack or
frame pointer as possible.  The only reason it was using custom code was
because PrologEpilogInserter assumed an x86-like layout, where the frame
pointer is at the opposite end of the frame from the stack pointer.
This meant that when frame pointer elimination was disabled,
the slots ended up being as close as possible to the incoming
stack pointer, which is the opposite of what we want on SystemZ.

This patch adds a new knob to say which layout is used and converts
SystemZ to use target-independent scavenging slots.  It's one of the pieces
needed to support frame-to-frame MVCs, where two slots might be required.

The ABI requires us to allocate 160 bytes for calls, so one approach
would be to use that area as temporary spill space instead.  It would need
some surgery to make sure that the slot isn't live across a call though.

I stuck to the "isFPCloseToIncomingSP - ..." style comment on the
"do what the surrounding code does" principle.  The FP case is already
covered by several Systemz/frame-* tests, which fail without the
PrologueEpilogueInserter change, so no new ones are needed.

No behavioural change intended.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185696 91177308-0d34-0410-b5e6-96231b3b80d8

6 files changed, 29 insertions, 62 deletions

diff --git a/include/llvm/Target/TargetFrameLowering.h b/include/llvm/Target/TargetFrameLowering.h
index d5f30f40ad..a60147f5c0 100644
--- a/include/llvm/Target/TargetFrameLowering.h
+++ b/include/llvm/Target/TargetFrameLowering.h
@@ -88,6 +88,11 @@ public:
   ///
   int getOffsetOfLocalArea() const { return LocalAreaOffset; }
 
+  /// isFPCloseToIncomingSP - Return true if the frame pointer is close to
+  /// the incoming stack pointer, false if it is close to the post-prologue
+  /// stack pointer.
+  virtual bool isFPCloseToIncomingSP() const { return true; }
+
   /// getCalleeSavedSpillSlots - This method returns a pointer to an array of
   /// pairs, that contains an entry for each callee saved register that must be
   /// spilled to a particular stack location if it is spilled.
diff --git a/lib/CodeGen/PrologEpilogInserter.cpp b/lib/CodeGen/PrologEpilogInserter.cpp
index 5fd671cf91..2b336d9ffa 100644
--- a/lib/CodeGen/PrologEpilogInserter.cpp
+++ b/lib/CodeGen/PrologEpilogInserter.cpp
@@ -558,10 +558,14 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
   unsigned MaxAlign = MFI->getMaxAlignment();
 
   // Make sure the special register scavenging spill slot is closest to the
-  // frame pointer if a frame pointer is required.
+  // incoming stack pointer if a frame pointer is required and is closer
+  // to the incoming rather than the final stack pointer.
   const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
-  if (RS && TFI.hasFP(Fn) && RegInfo->useFPForScavengingIndex(Fn) &&
-      !RegInfo->needsStackRealignment(Fn)) {
+  bool EarlyScavengingSlots = (TFI.hasFP(Fn) &&
+                               TFI.isFPCloseToIncomingSP() &&
+                               RegInfo->useFPForScavengingIndex(Fn) &&
+                               !RegInfo->needsStackRealignment(Fn));
+  if (RS && EarlyScavengingSlots) {
     SmallVector<int, 2> SFIs;
     RS->getScavengingFrameIndices(SFIs);
     for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
@@ -645,8 +649,7 @@ void PEI::calculateFrameObjectOffsets(MachineFunction &Fn) {
 
   // Make sure the special register scavenging spill slot is closest to the
   // stack pointer.
-  if (RS && (!TFI.hasFP(Fn) || RegInfo->needsStackRealignment(Fn) ||
-             !RegInfo->useFPForScavengingIndex(Fn))) {
+  if (RS && !EarlyScavengingSlots) {
     SmallVector<int, 2> SFIs;
     RS->getScavengingFrameIndices(SFIs);
     for (SmallVectorImpl<int>::iterator I = SFIs.begin(),
diff --git a/lib/Target/SystemZ/SystemZFrameLowering.cpp b/lib/Target/SystemZ/SystemZFrameLowering.cpp
index cd80d4e5ba..3ae59782f6 100644
--- a/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/lib/Target/SystemZ/SystemZFrameLowering.cpp
@@ -14,6 +14,7 @@
 #include "SystemZTargetMachine.h"
 #include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/RegisterScavenging.h"
 #include "llvm/IR/Function.h"
 
 using namespace llvm;
@@ -263,6 +264,18 @@ restoreCalleeSavedRegisters(MachineBasicBlock &MBB,
   return true;
 }
 
+void SystemZFrameLowering::
+processFunctionBeforeFrameFinalized(MachineFunction &MF,
+                                    RegScavenger *RS) const {
+  MachineFrameInfo *MFFrame = MF.getFrameInfo();
+  uint64_t MaxReach = (MFFrame->estimateStackSize(MF) +
+                       SystemZMC::CallFrameSize * 2);
+  if (!isUInt<12>(MaxReach))
+    // We may need a register scavenging slot if some parts of the frame
+    // are outside the reach of an unsigned 12-bit displacement.
+    RS->addScavengingFrameIndex(MFFrame->CreateStackObject(8, 8, false));
+}
+
 // Emit instructions before MBBI (in MBB) to add NumBytes to Reg.
 static void emitIncrement(MachineBasicBlock &MBB,
                           MachineBasicBlock::iterator &MBBI,
@@ -469,9 +482,6 @@ getAllocatedStackSize(const MachineFunction &MF) const {
   // Start with the size of the local variables and spill slots.
   uint64_t StackSize = MFFrame->getStackSize();
 
-  // Include space for an emergency spill slot, if one might be needed.
-  StackSize += getEmergencySpillSlotSize(MF);
-
   // We need to allocate the ABI-defined 160-byte base area whenever
   // we allocate stack space for our own use and whenever we call another
   // function.
@@ -481,19 +491,6 @@ getAllocatedStackSize(const MachineFunction &MF) const {
   return StackSize;
 }
 
-unsigned SystemZFrameLowering::
-getEmergencySpillSlotSize(const MachineFunction &MF) const {
-  const MachineFrameInfo *MFFrame = MF.getFrameInfo();
-  uint64_t MaxReach = MFFrame->getStackSize() + SystemZMC::CallFrameSize * 2;
-  return isUInt<12>(MaxReach) ? 0 : 8;
-}
-
-unsigned SystemZFrameLowering::
-getEmergencySpillSlotOffset(const MachineFunction &MF) const {
-  assert(getEmergencySpillSlotSize(MF) && "No emergency spill slot");
-  return SystemZMC::CallFrameSize;
-}
-
 bool
 SystemZFrameLowering::hasReservedCallFrame(const MachineFunction &MF) const {
   // The ABI requires us to allocate 160 bytes of stack space for the callee,
diff --git a/lib/Target/SystemZ/SystemZFrameLowering.h b/lib/Target/SystemZ/SystemZFrameLowering.h
index 08321e05a3..9b0a1d5f22 100644
--- a/lib/Target/SystemZ/SystemZFrameLowering.h
+++ b/lib/Target/SystemZ/SystemZFrameLowering.h
@@ -30,6 +30,7 @@ public:
                        const SystemZSubtarget &sti);
 
   // Override TargetFrameLowering.
+  virtual bool isFPCloseToIncomingSP() const LLVM_OVERRIDE { return false; }
   virtual const SpillSlot *getCalleeSavedSpillSlots(unsigned &NumEntries) const
     LLVM_OVERRIDE;
   virtual void
@@ -47,6 +48,8 @@ public:
                                 const std::vector<CalleeSavedInfo> &CSI,
                                 const TargetRegisterInfo *TRI) const
     LLVM_OVERRIDE;
+  virtual void processFunctionBeforeFrameFinalized(MachineFunction &MF,
+                                                   RegScavenger *RS) const;
   virtual void emitPrologue(MachineFunction &MF) const LLVM_OVERRIDE;
   virtual void emitEpilogue(MachineFunction &MF,
                             MachineBasicBlock &MBB) const LLVM_OVERRIDE;
@@ -64,16 +67,6 @@ public:
   // Return the number of bytes in the callee-allocated part of the frame.
   uint64_t getAllocatedStackSize(const MachineFunction &MF) const;
 
-  // Return the number of frame bytes that should be reserved for
-  // an emergency spill slot, for use by the register scaveneger.
-  // Return 0 if register scaveging won't be needed.
-  unsigned getEmergencySpillSlotSize(const MachineFunction &MF) const;
-
-  // Return the offset from the frame pointer of the emergency spill slot,
-  // which always fits within a 12-bit unsigned displacement field.
-  // Only valid if getEmergencySpillSlotSize(MF) returns nonzero.
-  unsigned getEmergencySpillSlotOffset(const MachineFunction &MF) const;
-
   // Return the byte offset from the incoming stack pointer of Reg's
   // ABI-defined save slot.  Return 0 if no slot is defined for Reg.
   unsigned getRegSpillOffset(unsigned Reg) const {
diff --git a/lib/Target/SystemZ/SystemZRegisterInfo.cpp b/lib/Target/SystemZ/SystemZRegisterInfo.cpp
index c695bb3dad..8ce6d6ab44 100644
--- a/lib/Target/SystemZ/SystemZRegisterInfo.cpp
+++ b/lib/Target/SystemZ/SystemZRegisterInfo.cpp
@@ -53,32 +53,6 @@ SystemZRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
   return Reserved;
 }
 
-bool
-SystemZRegisterInfo::saveScavengerRegister(MachineBasicBlock &MBB,
-					   MachineBasicBlock::iterator SaveMBBI,
-					   MachineBasicBlock::iterator &UseMBBI,
-					   const TargetRegisterClass *RC,
-					   unsigned Reg) const {
-  MachineFunction &MF = *MBB.getParent();
-  const SystemZInstrInfo &TII =
-    *static_cast<const SystemZInstrInfo*>(TM.getInstrInfo());
-  const SystemZFrameLowering *TFI =
-    static_cast<const SystemZFrameLowering *>(TM.getFrameLowering());
-  unsigned Base = getFrameRegister(MF);
-  uint64_t Offset = TFI->getEmergencySpillSlotOffset(MF);
-  DebugLoc DL;
-
-  unsigned LoadOpcode, StoreOpcode;
-  TII.getLoadStoreOpcodes(RC, LoadOpcode, StoreOpcode);
-
-  // The offset must always be in range of a 12-bit unsigned displacement.
-  BuildMI(MBB, SaveMBBI, DL, TII.get(StoreOpcode))
-    .addReg(Reg, RegState::Kill).addReg(Base).addImm(Offset).addReg(0);
-  BuildMI(MBB, UseMBBI, DL, TII.get(LoadOpcode), Reg)
-    .addReg(Base).addImm(Offset).addReg(0);
-  return true;
-}
-
 void
 SystemZRegisterInfo::eliminateFrameIndex(MachineBasicBlock::iterator MI,
                                          int SPAdj, unsigned FIOperandNum,
diff --git a/lib/Target/SystemZ/SystemZRegisterInfo.h b/lib/Target/SystemZ/SystemZRegisterInfo.h
index 047cb4a632..c447e4d5b8 100644
--- a/lib/Target/SystemZ/SystemZRegisterInfo.h
+++ b/lib/Target/SystemZ/SystemZRegisterInfo.h
@@ -52,11 +52,6 @@ public:
     const LLVM_OVERRIDE;
   virtual BitVector getReservedRegs(const MachineFunction &MF)
     const LLVM_OVERRIDE;
-  virtual bool saveScavengerRegister(MachineBasicBlock &MBB,
-                                     MachineBasicBlock::iterator SaveMBBI,
-                                     MachineBasicBlock::iterator &UseMBBI,
-                                     const TargetRegisterClass *RC,
-                                     unsigned Reg) const LLVM_OVERRIDE;
   virtual void eliminateFrameIndex(MachineBasicBlock::iterator MI,
                                    int SPAdj, unsigned FIOperandNum,
                                    RegScavenger *RS) const LLVM_OVERRIDE;