[MachineOutliner][AArch64] Add support for saving LR to a register

This teaches the outliner to save LR to a register rather than the stack when
possible. This allows us to avoid bumping the stack in outlined functions in
some cases. By doing this, in a later patch, we can teach the outliner to do
something like this:

f1:
  ...
  bl OUTLINED_FUNCTION
  ...

f2:
  ...
  move LR's contents to a register
  bl OUTLINED_FUNCTION
  move the register's contents back

instead of falling back to saving LR in both cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@338278 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 14 insertions, 0 deletions

diff --git a/include/llvm/CodeGen/MachineOutliner.h b/include/llvm/CodeGen/MachineOutliner.h
index 4249a99a891..95bfc24b57f 100644
--- a/include/llvm/CodeGen/MachineOutliner.h
+++ b/include/llvm/CodeGen/MachineOutliner.h
@@ -19,6 +19,7 @@
 #include "llvm/CodeGen/LiveRegUnits.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/TargetRegisterInfo.h"
+#include "llvm/CodeGen/LivePhysRegs.h"
 
 namespace llvm {
 namespace outliner {
@@ -74,6 +75,13 @@ public:
   /// cost model information.
   LiveRegUnits LRU;
 
+  /// Contains the accumulated register liveness information for the
+  /// instructions in this \p Candidate.
+  ///
+  /// This is optionally used by the target to determine which registers have
+  /// been used across the sequence.
+  LiveRegUnits UsedInSequence;
+
   /// Return the number of instructions in this Candidate.
   unsigned getLength() const { return Len; }
 
@@ -137,6 +145,12 @@ public:
     // outlining candidate.
     std::for_each(MBB->rbegin(), (MachineBasicBlock::reverse_iterator)front(),
                   [this](MachineInstr &MI) { LRU.stepBackward(MI); });
+
+    // Walk over the sequence itself and figure out which registers were used
+    // in the sequence.
+    UsedInSequence.init(TRI);
+    std::for_each(front(), std::next(back()),
+                  [this](MachineInstr &MI) { UsedInSequence.accumulate(MI); });
   }
 };