[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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@289933 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineBasicBlock.h

@@ -806,6 +806,28 @@ public:
   MachineBasicBlock::iterator getInitial() { return I; }
 };
 
+/// Increment \p It until it points to a non-debug instruction or to \p End
+/// and return the resulting iterator. This function should only be used
+/// MachineBasicBlock::{iterator, const_iterator, instr_iterator,
+/// const_instr_iterator} and the respective reverse iterators.
+template<typename IterT>
+inline IterT skipDebugInstructionsForward(IterT It, IterT End) {
+  while (It != End && It->isDebugValue())
+    It++;
+  return It;
+}
+
+/// Decrement \p It until it points to a non-debug instruction or to \p Begin
+/// and return the resulting iterator. This function should only be used
+/// MachineBasicBlock::{iterator, const_iterator, instr_iterator,
+/// const_instr_iterator} and the respective reverse iterators.
+template<class IterT>
+inline IterT skipDebugInstructionsBackward(IterT It, IterT Begin) {
+  while (It != Begin && It->isDebugValue())
+    It--;
+  return It;
+}
+
 } // End llvm namespace
 
 #endif

lib/CodeGen/BranchFolding.cpp

@@ -1733,10 +1733,8 @@ MachineBasicBlock::iterator findHoistingInsertPosAndDeps(MachineBasicBlock *MBB,
 
   // The terminator is probably a conditional branch, try not to separate the
   // branch from condition setting instruction.
-  MachineBasicBlock::iterator PI = Loc;
-  --PI;
-  while (PI != MBB->begin() && PI->isDebugValue())
-    --PI;
+  MachineBasicBlock::iterator PI =
+    skipDebugInstructionsBackward(std::prev(Loc), MBB->begin());
 
   bool IsDef = false;
   for (const MachineOperand &MO : PI->operands()) {
@@ -1830,18 +1828,11 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
   MachineBasicBlock::iterator FIE = FBB->end();
   while (TIB != TIE && FIB != FIE) {
     // Skip dbg_value instructions. These do not count.
-    if (TIB->isDebugValue()) {
-      while (TIB != TIE && TIB->isDebugValue())
-        ++TIB;
-      if (TIB == TIE)
-        break;
-    }
-    if (FIB->isDebugValue()) {
-      while (FIB != FIE && FIB->isDebugValue())
-        ++FIB;
-      if (FIB == FIE)
-        break;
-    }
+    TIB = skipDebugInstructionsForward(TIB, TIE);
+    FIB = skipDebugInstructionsForward(FIB, FIE);
+    if (TIB == TIE || FIB == FIE)
+      break;
+
     if (!TIB->isIdenticalTo(*FIB, MachineInstr::CheckKillDead))
       break;
 

lib/CodeGen/IfConversion.cpp

@@ -588,18 +588,6 @@ bool IfConverter::ValidTriangle(BBInfo &TrueBBI, BBInfo &FalseBBI,
   return TExit && TExit == FalseBBI.BB;
 }
 
-/// Increment \p It until it points to a non-debug instruction or to \p End.
-/// @param It Iterator to increment
-/// @param End Iterator that points to end. Will be compared to It
-/// @returns true if It == End, false otherwise.
-static inline bool skipDebugInstructionsForward(
-    MachineBasicBlock::iterator &It,
-    MachineBasicBlock::iterator &End) {
-  while (It != End && It->isDebugValue())
-    It++;
-  return It == End;
-}
-
 /// Shrink the provided inclusive range by one instruction.
 /// If the range was one instruction (\p It == \p Begin), It is not modified,
 /// but \p Empty is set to true.
@@ -613,21 +601,6 @@ static inline void shrinkInclusiveRange(
     It--;
 }
 
-/// Decrement \p It until it points to a non-debug instruction or the range is
-/// empty.
-/// @param It Iterator to decrement.
-/// @param Begin Iterator that points to beginning. Will be compared to It
-/// @param Empty Set to true if the resulting range is Empty
-/// @returns the value of Empty as a convenience.
-static inline bool skipDebugInstructionsBackward(
-    MachineBasicBlock::iterator &Begin,
-    MachineBasicBlock::iterator &It,
-    bool &Empty) {
-  while (!Empty && It->isDebugValue())
-    shrinkInclusiveRange(Begin, It, Empty);
-  return Empty;
-}
-
 /// Count duplicated instructions and move the iterators to show where they
 /// are.
 /// @param TIB True Iterator Begin
@@ -659,9 +632,11 @@ bool IfConverter::CountDuplicatedInstructions(
 
   while (TIB != TIE && FIB != FIE) {
     // Skip dbg_value instructions. These do not count.
-    if(skipDebugInstructionsForward(TIB, TIE))
+    TIB = skipDebugInstructionsForward(TIB, TIE);
+    if(TIB == TIE)
       break;
-    if(skipDebugInstructionsForward(FIB, FIE))
+    FIB = skipDebugInstructionsForward(FIB, FIE);
+    if(FIB == FIE)
       break;
     if (!TIB->isIdenticalTo(*FIB))
       break;
@@ -718,9 +693,11 @@ bool IfConverter::CountDuplicatedInstructions(
   // Count duplicate instructions at the ends of the blocks.
   while (!TEmpty && !FEmpty) {
     // Skip dbg_value instructions. These do not count.
-    if (skipDebugInstructionsBackward(TIB, TIE, TEmpty))
-      break;
-    if (skipDebugInstructionsBackward(FIB, FIE, FEmpty))
+    TIE = skipDebugInstructionsBackward(TIE, TIB);
+    FIE = skipDebugInstructionsBackward(FIE, FIB);
+    TEmpty = TIE == TIB && TIE->isDebugValue();
+    FEmpty = FIE == FIB && FIE->isDebugValue();
+    if (TEmpty || FEmpty)
       break;
     if (!TIE->isIdenticalTo(*FIE))
       break;
@@ -770,8 +747,11 @@ static void verifySameBranchInstructions(
   MachineBasicBlock::iterator E2 = std::prev(MBB2->end());
   bool Empty1 = false, Empty2 = false;
   while (!Empty1 && !Empty2) {
-    skipDebugInstructionsBackward(B1, E1, Empty1);
-    skipDebugInstructionsBackward(B2, E2, Empty2);
+    E1 = skipDebugInstructionsBackward(E1, B1);
+    E2 = skipDebugInstructionsBackward(E2, B2);
+    Empty1 = E1 == B1 && E1->isDebugValue();
+    Empty2 = E2 == B2 && E2->isDebugValue();
+
     if (Empty1 && Empty2)
       break;
 

lib/CodeGen/MachineBasicBlock.cpp

@@ -191,10 +191,7 @@ MachineBasicBlock::instr_iterator MachineBasicBlock::getFirstInstrTerminator() {
 
 MachineBasicBlock::iterator MachineBasicBlock::getFirstNonDebugInstr() {
   // Skip over begin-of-block dbg_value instructions.
-  iterator I = begin(), E = end();
-  while (I != E && I->isDebugValue())
-    ++I;
-  return I;
+  return skipDebugInstructionsForward(begin(), end());
 }
 
 MachineBasicBlock::iterator MachineBasicBlock::getLastNonDebugInstr() {
@@ -1140,17 +1137,11 @@ bool MachineBasicBlock::CorrectExtraCFGEdges(MachineBasicBlock *DestA,
 /// instructions.  Return UnknownLoc if there is none.
 DebugLoc
 MachineBasicBlock::findDebugLoc(instr_iterator MBBI) {
-  DebugLoc DL;
-  instr_iterator E = instr_end();
-  if (MBBI == E)
-    return DL;
-
   // Skip debug declarations, we don't want a DebugLoc from them.
-  while (MBBI != E && MBBI->isDebugValue())
-    MBBI++;
-  if (MBBI != E)
-    DL = MBBI->getDebugLoc();
-  return DL;
+  MBBI = skipDebugInstructionsForward(MBBI, instr_end());
+  if (MBBI != instr_end())
+    return MBBI->getDebugLoc();
+  return {};
 }
 
 /// Return probability of the edge from this block to MBB.

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.

lib/CodeGen/RegisterPressure.cpp

@@ -266,9 +266,8 @@ bool RegPressureTracker::isBottomClosed() const {
 
 
 SlotIndex RegPressureTracker::getCurrSlot() const {
-  MachineBasicBlock::const_iterator IdxPos = CurrPos;
-  while (IdxPos != MBB->end() && IdxPos->isDebugValue())
-    ++IdxPos;
+  MachineBasicBlock::const_iterator IdxPos =
+    skipDebugInstructionsForward(CurrPos, MBB->end());
   if (IdxPos == MBB->end())
     return LIS->getMBBEndIdx(MBB);
   return LIS->getInstructionIndex(*IdxPos).getRegSlot();
@@ -817,9 +816,7 @@ void RegPressureTracker::recedeSkipDebugValues() {
     static_cast<RegionPressure&>(P).openTop(CurrPos);
 
   // Find the previous instruction.
-  do
-    --CurrPos;
-  while (CurrPos != MBB->begin() && CurrPos->isDebugValue());
+  CurrPos = skipDebugInstructionsBackward(std::prev(CurrPos), MBB->begin());
 
   SlotIndex SlotIdx;
   if (RequireIntervals)
@@ -895,9 +892,7 @@ void RegPressureTracker::advance(const RegisterOperands &RegOpers) {
   bumpDeadDefs(RegOpers.DeadDefs);
 
   // Find the next instruction.
-  do
-    ++CurrPos;
-  while (CurrPos != MBB->end() && CurrPos->isDebugValue());
+  CurrPos = skipDebugInstructionsForward(std::next(CurrPos), MBB->end());
 }
 
 void RegPressureTracker::advance() {