[codegen] Add generic functions to skip debug values.

Summary:
This commits moves skipDebugInstructionsForward and
skipDebugInstructionsBackward from lib/CodeGen/IfConversion.cpp
to include/llvm/CodeGen/MachineBasicBlock.h and updates
some codgen files to use them.

This refactoring was suggested in https://reviews.llvm.org/D27688
and I thought it's best to do the refactoring in a separate
review, but I could also put both changes in a single review
if that's preferred.

Also, the names for the functions aren't the snappiest and
I would be happy to rename them if anybody has suggestions. 

Reviewers: eli.friedman, iteratee, aprantl, MatzeB

Subscribers: MatzeB, llvm-commits

Differential Revision: https://reviews.llvm.org/D27782

llvm-svn: 289933

1 files changed, 1 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/MachineCSE.cpp b/llvm/lib/CodeGen/MachineCSE.cpp
index 3299a575114..0766f465456 100644
--- a/llvm/lib/CodeGen/MachineCSE.cpp
+++ b/llvm/lib/CodeGen/MachineCSE.cpp
@@ -177,8 +177,7 @@ MachineCSE::isPhysDefTriviallyDead(unsigned Reg,
   unsigned LookAheadLeft = LookAheadLimit;
   while (LookAheadLeft) {
     // Skip over dbg_value's.
-    while (I != E && I->isDebugValue())
-      ++I;
+    I = skipDebugInstructionsForward(I, E);
 
     if (I == E)
       // Reached end of block, register is obviously dead.