Revert "[DebugInfo] MachineSink: find more DBG_VALUEs to sink"

This reverts commit f5e1b718a675a4449b71423f04d38e1e93045105.

PR43855 reports a performance regression with commit ee50590e. This commit
depends on the faulty one, so has to come out too.

1 files changed, 15 insertions, 86 deletions

diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index 81fd30c..4c55158a 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -105,9 +105,6 @@ namespace {
     using AllSuccsCache =
         std::map<MachineBasicBlock *, SmallVector<MachineBasicBlock *, 4>>;
 
-    // Remember debug uses of vregs seen, so we know what to sink out of blocks.
-    DenseMap<unsigned, TinyPtrVector<MachineInstr *>> SeenDbgUsers;
-
   public:
     static char ID; // Pass identification
 
@@ -135,7 +132,6 @@ namespace {
 
   private:
     bool ProcessBlock(MachineBasicBlock &MBB);
-    void ProcessDbgInst(MachineInstr &MI);
     bool isWorthBreakingCriticalEdge(MachineInstr &MI,
                                      MachineBasicBlock *From,
                                      MachineBasicBlock *To);
@@ -157,14 +153,8 @@ namespace {
                                    MachineBasicBlock *To,
                                    bool BreakPHIEdge);
     bool SinkInstruction(MachineInstr &MI, bool &SawStore,
-                         AllSuccsCache &AllSuccessors);
 
-    /// If we sink a COPY inst, some debug users of it's destination may no
-    /// longer be dominated by the COPY, and will eventually be dropped.
-    /// This is easily rectified by forwarding the non-dominated debug uses
-    /// to the copy source.
-    void SalvageUnsunkDebugUsersOfCopy(MachineInstr &,
-                                       MachineBasicBlock *TargetBlock);
+                         AllSuccsCache &AllSuccessors);
     bool AllUsesDominatedByBlock(unsigned Reg, MachineBasicBlock *MBB,
                                  MachineBasicBlock *DefMBB,
                                  bool &BreakPHIEdge, bool &LocalUse) const;
@@ -377,11 +367,8 @@ bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) {
     if (!ProcessedBegin)
       --I;
 
-    if (MI.isDebugInstr()) {
-      if (MI.isDebugValue())
-        ProcessDbgInst(MI);
+    if (MI.isDebugInstr())
       continue;
-    }
 
     bool Joined = PerformTrivialForwardCoalescing(MI, &MBB);
     if (Joined) {
@@ -397,23 +384,9 @@ bool MachineSinking::ProcessBlock(MachineBasicBlock &MBB) {
     // If we just processed the first instruction in the block, we're done.
   } while (!ProcessedBegin);
 
-  SeenDbgUsers.clear();
-
   return MadeChange;
 }
 
-void MachineSinking::ProcessDbgInst(MachineInstr &MI) {
-  // When we see DBG_VALUEs for registers, record any vreg it reads, so that
-  // we know what to sink if the vreg def sinks.
-  assert(MI.isDebugValue() && "Expected DBG_VALUE for processing");
-
-  MachineOperand &MO = MI.getOperand(0);
-  if (!MO.isReg() || !MO.getReg().isVirtual())
-    return;
-
-  SeenDbgUsers[MO.getReg()].push_back(&MI);
-}
-
 bool MachineSinking::isWorthBreakingCriticalEdge(MachineInstr &MI,
                                                  MachineBasicBlock *From,
                                                  MachineBasicBlock *To) {
@@ -758,13 +731,22 @@ static bool SinkingPreventsImplicitNullCheck(MachineInstr &MI,
          MBP.LHS.getReg() == BaseOp->getReg();
 }
 
-/// Sink an instruction and its associated debug instructions.
+/// Sink an instruction and its associated debug instructions. If the debug
+/// instructions to be sunk are already known, they can be provided in DbgVals.
 static void performSink(MachineInstr &MI, MachineBasicBlock &SuccToSinkTo,
                         MachineBasicBlock::iterator InsertPos,
-                        SmallVectorImpl<MachineInstr *> &DbgValuesToSink) {
+                        SmallVectorImpl<MachineInstr *> *DbgVals = nullptr) {
   const MachineRegisterInfo &MRI = MI.getMF()->getRegInfo();
   const TargetInstrInfo &TII = *MI.getMF()->getSubtarget().getInstrInfo();
 
+  // If debug values are provided use those, otherwise call collectDebugValues.
+  SmallVector<MachineInstr *, 2> DbgValuesToSink;
+  if (DbgVals)
+    DbgValuesToSink.insert(DbgValuesToSink.begin(),
+                           DbgVals->begin(), DbgVals->end());
+  else
+    MI.collectDebugValues(DbgValuesToSink);
+
   // If we cannot find a location to use (merge with), then we erase the debug
   // location to prevent debug-info driven tools from potentially reporting
   // wrong location information.
@@ -947,25 +929,7 @@ bool MachineSinking::SinkInstruction(MachineInstr &MI, bool &SawStore,
   while (InsertPos != SuccToSinkTo->end() && InsertPos->isPHI())
     ++InsertPos;
 
-  // Collect debug users of any vreg that this inst defines.
-  SmallVector<MachineInstr *, 4> DbgUsersToSink;
-  for (auto &MO : MI.operands()) {
-    if (!MO.isReg() || !MO.isDef() || !MO.getReg().isVirtual())
-      continue;
-    if (!SeenDbgUsers.count(MO.getReg()))
-      continue;
-
-    auto &Users = SeenDbgUsers[MO.getReg()];
-    DbgUsersToSink.insert(DbgUsersToSink.end(), Users.begin(), Users.end());
-  }
-
-  // After sinking, some debug users may not be dominated any more. If possible,
-  // copy-propagate their operands. As it's expensive, don't do this if there's
-  // no debuginfo in the program.
-  if (MI.getMF()->getFunction().getSubprogram() && MI.isCopy())
-    SalvageUnsunkDebugUsersOfCopy(MI, SuccToSinkTo);
-
-  performSink(MI, *SuccToSinkTo, InsertPos, DbgUsersToSink);
+  performSink(MI, *SuccToSinkTo, InsertPos);
 
   // Conservatively, clear any kill flags, since it's possible that they are no
   // longer correct.
@@ -980,41 +944,6 @@ bool MachineSinking::SinkInstruction(MachineInstr &MI, bool &SawStore,
   return true;
 }
 
-void MachineSinking::SalvageUnsunkDebugUsersOfCopy(
-    MachineInstr &MI, MachineBasicBlock *TargetBlock) {
-  assert(MI.isCopy());
-  assert(MI.getOperand(1).isReg());
-
-  // Enumerate all users of vreg operands that are def'd. Skip those that will
-  // be sunk. For the rest, if they are not dominated by the block we will sink
-  // MI into, propagate the copy source to them.
-  SmallVector<MachineInstr *, 4> DbgDefUsers;
-  const MachineRegisterInfo &MRI = MI.getMF()->getRegInfo();
-  for (auto &MO : MI.operands()) {
-    if (!MO.isReg() || !MO.isDef() || !MO.getReg().isVirtual())
-      continue;
-    for (auto &User : MRI.use_instructions(MO.getReg())) {
-      if (!User.isDebugValue() || DT->dominates(TargetBlock, User.getParent()))
-        continue;
-
-      // If is in same block, will either sink or be use-before-def.
-      if (User.getParent() == MI.getParent())
-        continue;
-
-      assert(User.getOperand(0).isReg() &&
-             "DBG_VALUE user of vreg, but non reg operand?");
-      DbgDefUsers.push_back(&User);
-    }
-  }
-
-  // Point the users of this copy that are no longer dominated, at the source
-  // of the copy.
-  for (auto *User : DbgDefUsers) {
-    User->getOperand(0).setReg(MI.getOperand(1).getReg());
-    User->getOperand(0).setSubReg(MI.getOperand(1).getSubReg());
-  }
-}
-
 //===----------------------------------------------------------------------===//
 // This pass is not intended to be a replacement or a complete alternative
 // for the pre-ra machine sink pass. It is only designed to sink COPY
@@ -1324,7 +1253,7 @@ bool PostRAMachineSinking::tryToSinkCopy(MachineBasicBlock &CurBB,
     // block.
     clearKillFlags(MI, CurBB, UsedOpsInCopy, UsedRegUnits, TRI);
     MachineBasicBlock::iterator InsertPos = SuccBB->getFirstNonPHI();
-    performSink(*MI, *SuccBB, InsertPos, DbgValsToSink);
+    performSink(*MI, *SuccBB, InsertPos, &DbgValsToSink);
     updateLiveIn(MI, SuccBB, UsedOpsInCopy, DefedRegsInCopy);
 
     Changed = true;