[MachineBasicBlock] Add helpers for skipping debug instructions [1/14]

Summary:
These helpers are exercised by follow-up commits in this patch series,
which is all about removing CodeGen differences with vs. without debug
info in the AArch64 backend.

Reviewers: fhahn, aprantl, jpaquette, paquette

Subscribers: kristof.beyls, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78260

include/llvm/CodeGen/MachineBasicBlock.h

@@ -1061,6 +1061,35 @@ inline IterT skipDebugInstructionsBackward(IterT It, IterT Begin) {
   return It;
 }
 
+/// Increment \p It, then continue incrementing it while it points to a debug
+/// instruction. A replacement for std::next.
+template <typename IterT> inline IterT next_nodbg(IterT It, IterT End) {
+  return skipDebugInstructionsForward(std::next(It), End);
+}
+
+/// Decrement \p It, then continue decrementing it while it points to a debug
+/// instruction. A replacement for std::prev.
+template <typename IterT> inline IterT prev_nodbg(IterT It, IterT Begin) {
+  return skipDebugInstructionsBackward(std::prev(It), Begin);
+}
+
+/// Construct a range iterator which begins at \p It and moves forwards until
+/// \p End is reached, skipping any debug instructions.
+template <typename IterT>
+inline auto instructionsWithoutDebug(IterT It, IterT End) {
+  return make_filter_range(make_range(It, End), [](const MachineInstr &MI) {
+    return !MI.isDebugInstr();
+  });
+}
+
+/// Construct a range iterator which begins at \p It and moves backwards until
+/// \p Begin is reached, skipping any debug instructions.
+template <typename IterT>
+inline auto reversedInstructionsWithoutDebug(IterT It, IterT Begin) {
+  return instructionsWithoutDebug(make_reverse_iterator(It),
+                                  make_reverse_iterator(Begin));
+}
+
 } // end namespace llvm
 
 #endif // LLVM_CODEGEN_MACHINEBASICBLOCK_H

lib/CodeGen/BranchFolding.cpp

@@ -1840,8 +1840,7 @@ 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 =
-    skipDebugInstructionsBackward(std::prev(Loc), MBB->begin());
+  MachineBasicBlock::iterator PI = prev_nodbg(Loc, MBB->begin());
 
   bool IsDef = false;
   for (const MachineOperand &MO : PI->operands()) {

lib/CodeGen/MachineBasicBlock.cpp

@@ -1329,8 +1329,8 @@ MachineBasicBlock::findDebugLoc(instr_iterator MBBI) {
 /// instructions.  Return UnknownLoc if there is none.
 DebugLoc MachineBasicBlock::findPrevDebugLoc(instr_iterator MBBI) {
   if (MBBI == instr_begin()) return {};
-  // Skip debug declarations, we don't want a DebugLoc from them.
-  MBBI = skipDebugInstructionsBackward(std::prev(MBBI), instr_begin());
+  // Skip debug instructions, we don't want a DebugLoc from them.
+  MBBI = prev_nodbg(MBBI, instr_begin());
   if (!MBBI->isDebugInstr()) return MBBI->getDebugLoc();
   return {};
 }

lib/CodeGen/RegisterPressure.cpp

@@ -858,7 +858,7 @@ void RegPressureTracker::recedeSkipDebugValues() {
     static_cast<RegionPressure&>(P).openTop(CurrPos);
 
   // Find the previous instruction.
-  CurrPos = skipDebugInstructionsBackward(std::prev(CurrPos), MBB->begin());
+  CurrPos = prev_nodbg(CurrPos, MBB->begin());
 
   SlotIndex SlotIdx;
   if (RequireIntervals && !CurrPos->isDebugInstr())
@@ -940,7 +940,7 @@ void RegPressureTracker::advance(const RegisterOperands &RegOpers) {
   bumpDeadDefs(RegOpers.DeadDefs);
 
   // Find the next instruction.
-  CurrPos = skipDebugInstructionsForward(std::next(CurrPos), MBB->end());
+  CurrPos = next_nodbg(CurrPos, MBB->end());
 }
 
 void RegPressureTracker::advance() {

lib/Target/X86/X86AvoidStoreForwardingBlocks.cpp

@@ -411,9 +411,8 @@ void X86AvoidSFBPass::buildCopy(MachineInstr *LoadInst, unsigned NLoadOpcode,
   // If the load and store are consecutive, use the loadInst location to
   // reduce register pressure.
   MachineInstr *StInst = StoreInst;
-  auto PrevInstrIt = skipDebugInstructionsBackward(
-      std::prev(MachineBasicBlock::instr_iterator(StoreInst)),
-      MBB->instr_begin());
+  auto PrevInstrIt = prev_nodbg(MachineBasicBlock::instr_iterator(StoreInst),
+                                MBB->instr_begin());
   if (PrevInstrIt.getNodePtr() == LoadInst)
     StInst = LoadInst;
   MachineInstr *NewStore =
@@ -499,9 +498,10 @@ void X86AvoidSFBPass::buildCopies(int Size, MachineInstr *LoadInst,
 static void updateKillStatus(MachineInstr *LoadInst, MachineInstr *StoreInst) {
   MachineOperand &LoadBase = getBaseOperand(LoadInst);
   MachineOperand &StoreBase = getBaseOperand(StoreInst);
-  auto StorePrevNonDbgInstr = skipDebugInstructionsBackward(
-          std::prev(MachineBasicBlock::instr_iterator(StoreInst)),
-          LoadInst->getParent()->instr_begin()).getNodePtr();
+  auto StorePrevNonDbgInstr =
+      prev_nodbg(MachineBasicBlock::instr_iterator(StoreInst),
+                 LoadInst->getParent()->instr_begin())
+          .getNodePtr();
   if (LoadBase.isReg()) {
     MachineInstr *LastLoad = LoadInst->getPrevNode();
     // If the original load and store to xmm/ymm were consecutive

lib/Target/X86/X86ISelLowering.cpp

@@ -31494,8 +31494,7 @@ X86TargetLowering::EmitLoweredSelect(MachineInstr &MI,
            (NextMIIt->getOperand(3).getImm() == CC ||
             NextMIIt->getOperand(3).getImm() == OppCC)) {
       LastCMOV = &*NextMIIt;
-      ++NextMIIt;
-      NextMIIt = skipDebugInstructionsForward(NextMIIt, ThisMBB->end());
+      NextMIIt = next_nodbg(NextMIIt, ThisMBB->end());
     }
   }