[ARM] Make the frame lowering code ready for shrink-wrapping.

Shrink-wrapping can now be tested on ARM with -enable-shrink-wrap.

Related to <rdar://problem/20821730>

llvm-svn: 242908

1 files changed, 36 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/Thumb1FrameLowering.h b/llvm/lib/Target/ARM/Thumb1FrameLowering.h
index 31d57325ebd..812f9830824 100644
--- a/llvm/lib/Target/ARM/Thumb1FrameLowering.h
+++ b/llvm/lib/Target/ARM/Thumb1FrameLowering.h
@@ -45,6 +45,42 @@ public:
   eliminateCallFramePseudoInstr(MachineFunction &MF,
                                 MachineBasicBlock &MBB,
                                 MachineBasicBlock::iterator MI) const override;
+
+  /// Check whether or not the given \p MBB can be used as a epilogue
+  /// for the target.
+  /// The epilogue will be inserted before the first terminator of that block.
+  /// This method is used by the shrink-wrapping pass to decide if
+  /// \p MBB will be correctly handled by the target.
+  bool canUseAsEpilogue(const MachineBasicBlock &MBB) const override;
+
+private:
+  /// Check if the frame lowering of \p MF needs a special fixup
+  /// code sequence for the epilogue.
+  /// Unlike T2 and ARM mode, the T1 pop instruction cannot restore
+  /// to LR, and we can't pop the value directly to the PC when
+  /// we need to update the SP after popping the value. So instead
+  /// we have to emit:
+  ///   POP {r3}
+  ///   ADD sp, #offset
+  ///   BX r3
+  /// If this would clobber a return value, then generate this sequence instead:
+  ///   MOV ip, r3
+  ///   POP {r3}
+  ///   ADD sp, #offset
+  ///   MOV lr, r3
+  ///   MOV r3, ip
+  ///   BX lr
+  bool needPopSpecialFixUp(const MachineFunction &MF) const;
+
+  /// Emit the special fixup code sequence for the epilogue.
+  /// \see needPopSpecialFixUp for more details.
+  /// \p DoIt, tells this method whether or not to actually insert
+  /// the code sequence in \p MBB. I.e., when \p DoIt is false,
+  /// \p MBB is left untouched.
+  /// \returns For \p DoIt == true: True when the emission succeeded
+  /// false otherwise. For \p DoIt == false: True when the emission
+  /// would have been possible, false otherwise.
+  bool emitPopSpecialFixUp(MachineBasicBlock &MBB, bool DoIt) const;
 };
 
 } // End llvm namespace