[ARM] Remove unused declaration isSafeToDefineLR

The corresponding function definition was removed by:

  commit e82a0084d322948b94a5ca3213237d5eeab4920f
  Author: Sam Parker <sam.parker@arm.com>
  Date:   Fri Sep 25 09:36:40 2020 +0100

diff --git a/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp b/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
index 1e0a7d1..247730c 100644 (file)
--- a/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
+++ b/llvm/lib/Target/ARM/ARMLowOverheadLoops.cpp
@@ -427,11 +427,6 @@ namespace {
     // after tail predication conversion.
     bool ValidateLiveOuts();
 
-    // Is it safe to define LR with DLS/WLS?
-    // LR can be defined if it is the operand to start, because it's the same
-    // value, or if it's going to be equivalent to the operand to Start.
-    MachineInstr *isSafeToDefineLR();
-
     // Check the branch targets are within range and we satisfy our
     // restrictions.
     void Validate(ARMBasicBlockUtils *BBUtils);