[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.

llvm-svn: 185696

1 files changed, 13 insertions, 16 deletions

diff --git a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp b/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
index cd80d4e5ba2..3ae59782f60 100644
--- a/llvm/lib/Target/SystemZ/SystemZFrameLowering.cpp
+++ b/llvm/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,