[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

1 files changed, 3 insertions, 10 deletions

diff --git a/lib/Target/SystemZ/SystemZFrameLowering.h b/lib/Target/SystemZ/SystemZFrameLowering.h
index 08321e0..9b0a1d5 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 {