[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, 5 insertions, 0 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.