1 files changed, 17 insertions, 37 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugValues.cpp b/llvm/lib/CodeGen/LiveDebugValues.cpp
index 1ddcceabe20..cd39950e392 100644
--- a/llvm/lib/CodeGen/LiveDebugValues.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues.cpp
@@ -385,7 +385,7 @@ private:
   void process(MachineInstr &MI, OpenRangesSet &OpenRanges,
                VarLocInMBB &OutLocs, VarLocMap &VarLocIDs,
                TransferMap &Transfers, DebugParamMap &DebugEntryVals,
-               bool transferChanges, OverlapMap &OverlapFragments,
+               OverlapMap &OverlapFragments,
                VarToFragments &SeenFragments);
 
   void accumulateFragmentMap(MachineInstr &MI, VarToFragments &SeenFragments,
@@ -1015,21 +1015,15 @@ void LiveDebugValues::accumulateFragmentMap(MachineInstr &MI,
 /// This routine creates OpenRanges and OutLocs.
 void LiveDebugValues::process(MachineInstr &MI, OpenRangesSet &OpenRanges,
                               VarLocInMBB &OutLocs, VarLocMap &VarLocIDs,
-                              TransferMap &Transfers, DebugParamMap &DebugEntryVals,
-                              bool transferChanges,
+                              TransferMap &Transfers,
+                              DebugParamMap &DebugEntryVals,
                               OverlapMap &OverlapFragments,
                               VarToFragments &SeenFragments) {
   transferDebugValue(MI, OpenRanges, VarLocIDs);
   transferRegisterDef(MI, OpenRanges, VarLocIDs, Transfers,
                       DebugEntryVals);
-  if (transferChanges) {
-    transferRegisterCopy(MI, OpenRanges, VarLocIDs, Transfers);
-    transferSpillOrRestoreInst(MI, OpenRanges, VarLocIDs, Transfers);
-  } else {
-    // Build up a map of overlapping fragments on the first run through.
-    if (MI.isDebugValue())
-      accumulateFragmentMap(MI, SeenFragments, OverlapFragments);
-  }
+  transferRegisterCopy(MI, OpenRanges, VarLocIDs, Transfers);
+  transferSpillOrRestoreInst(MI, OpenRanges, VarLocIDs, Transfers);
 }
 
 /// This routine joins the analysis results of all incoming edges in @MBB by
@@ -1050,9 +1044,11 @@ bool LiveDebugValues::join(
   // can be joined.
   int NumVisited = 0;
   for (auto p : MBB.predecessors()) {
-    // Ignore unvisited predecessor blocks.  As we are processing
-    // the blocks in reverse post-order any unvisited block can
-    // be considered to not remove any incoming values.
+    // Ignore backedges if we have not visited the predecessor yet. As the
+    // predecessor hasn't yet had locations propagated into it, most locations
+    // will not yet be valid, so treat them as all being uninitialized and
+    // potentially valid. If a location guessed to be correct here is
+    // invalidated later, we will remove it when we revisit this block.
     if (!Visited.count(p)) {
       LLVM_DEBUG(dbgs() << "  ignoring unvisited pred MBB: " << p->getNumber()
                         << "\n");
@@ -1215,8 +1211,6 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
                       std::greater<unsigned int>>
       Pending;
 
-  enum : bool { dontTransferChanges = false, transferChanges = true };
-
   // Besides parameter's modification, check whether a DBG_VALUE is inlined
   // in order to deduce whether the variable that it tracks comes from
   // a different function. If that is the case we can't track its entry value.
@@ -1254,27 +1248,14 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
         !MI.getDebugExpression()->isFragment())
       DebugEntryVals[MI.getDebugVariable()] = &MI;
 
-  // Initialize every mbb with OutLocs.
-  // We are not looking at any spill instructions during the initial pass
-  // over the BBs. The LiveDebugVariables pass has already created DBG_VALUE
-  // instructions for spills of registers that are known to be user variables
-  // within the BB in which the spill occurs.
+  // Initialize per-block structures and scan for fragment overlaps.
   for (auto &MBB : MF) {
+    PendingInLocs[&MBB] = VarLocSet();
+
     for (auto &MI : MBB) {
-      process(MI, OpenRanges, OutLocs, VarLocIDs, Transfers, DebugEntryVals,
-              dontTransferChanges, OverlapFragments, SeenFragments);
-    }
-    transferTerminator(&MBB, OpenRanges, OutLocs, VarLocIDs);
-    // Add any entry DBG_VALUE instructions necessitated by parameter
-    // clobbering.
-    for (auto &TR : Transfers) {
-      MBB.insertAfter(MachineBasicBlock::iterator(*TR.TransferInst),
-                     TR.DebugInst);
+      if (MI.isDebugValue())
+        accumulateFragmentMap(MI, SeenFragments, OverlapFragments);
     }
-    Transfers.clear();
-
-    // Initialize pending inlocs.
-    PendingInLocs[&MBB] = VarLocSet();
   }
 
   auto hasNonArtificialLocation = [](const MachineInstr &MI) -> bool {
@@ -1313,7 +1294,7 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
       Worklist.pop();
       MBBJoined = join(*MBB, OutLocs, InLocs, VarLocIDs, Visited,
                        ArtificialBlocks, PendingInLocs);
-      Visited.insert(MBB);
+      MBBJoined |= Visited.insert(MBB).second;
       if (MBBJoined) {
         MBBJoined = false;
         Changed = true;
@@ -1324,8 +1305,7 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) {
         OpenRanges.insertFromLocSet(PendingInLocs[MBB], VarLocIDs);
         for (auto &MI : *MBB)
               process(MI, OpenRanges, OutLocs, VarLocIDs, Transfers,
-                      DebugEntryVals, transferChanges, OverlapFragments,
-                      SeenFragments);
+                      DebugEntryVals, OverlapFragments, SeenFragments);
         OLChanged |= transferTerminator(MBB, OpenRanges, OutLocs, VarLocIDs);
 
         // Add any DBG_VALUE instructions necessitated by spills.