Fix PR24563 (LiveDebugVariables unconditionally propagates all DBG_VALUEs)

LiveDebugVariables unconditionally propagates all DBG_VALUE down the
dominator tree, which happens to work fine if there already is another
DBG_VALUE or the DBG_VALUE happends to describe a single-assignment vreg
but is otherwise wrong if the DBG_VALUE is coming from only one of the
predecessors.

In r255759 we introduced a proper data flow analysis scheduled after
LiveDebugVariables that correctly propagates DBG_VALUEs across basic block
boundaries. With the new pass in place, the incorrect propagation in
LiveDebugVariables can be retired witout loosing any of the benefits
where LiveDebugVariables happened to do the right thing.

llvm-svn: 256188

1 files changed, 36 insertions, 52 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugVariables.cpp b/llvm/lib/CodeGen/LiveDebugVariables.cpp
index 6543287..6dac7db 100644
--- a/llvm/lib/CodeGen/LiveDebugVariables.cpp
+++ b/llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -534,65 +534,49 @@ bool LDVImpl::collectDebugValues(MachineFunction &mf) {
   return Changed;
 }
 
-void UserValue::extendDef(SlotIndex Idx, unsigned LocNo,
-                          LiveRange *LR, const VNInfo *VNI,
-                          SmallVectorImpl<SlotIndex> *Kills,
+/// We only propagate DBG_VALUES locally here. LiveDebugValues performs a
+/// data-flow analysis to propagate them beyond basic block boundaries.
+void UserValue::extendDef(SlotIndex Idx, unsigned LocNo, LiveRange *LR,
+                          const VNInfo *VNI, SmallVectorImpl<SlotIndex> *Kills,
                           LiveIntervals &LIS, MachineDominatorTree &MDT,
                           UserValueScopes &UVS) {
-  SmallVector<SlotIndex, 16> Todo;
-  Todo.push_back(Idx);
-  do {
-    SlotIndex Start = Todo.pop_back_val();
-    MachineBasicBlock *MBB = LIS.getMBBFromIndex(Start);
-    SlotIndex Stop = LIS.getMBBEndIdx(MBB);
-    LocMap::iterator I = locInts.find(Start);
-
-    // Limit to VNI's live range.
-    bool ToEnd = true;
-    if (LR && VNI) {
-      LiveInterval::Segment *Segment = LR->getSegmentContaining(Start);
-      if (!Segment || Segment->valno != VNI) {
-        if (Kills)
-          Kills->push_back(Start);
-        continue;
-      }
-      if (Segment->end < Stop)
-        Stop = Segment->end, ToEnd = false;
-    }
-
-    // There could already be a short def at Start.
-    if (I.valid() && I.start() <= Start) {
-      // Stop when meeting a different location or an already extended interval.
-      Start = Start.getNextSlot();
-      if (I.value() != LocNo || I.stop() != Start)
-        continue;
-      // This is a one-slot placeholder. Just skip it.
-      ++I;
+  SlotIndex Start = Idx;
+  MachineBasicBlock *MBB = LIS.getMBBFromIndex(Start);
+  SlotIndex Stop = LIS.getMBBEndIdx(MBB);
+  LocMap::iterator I = locInts.find(Start);
+
+  // Limit to VNI's live range.
+  bool ToEnd = true;
+  if (LR && VNI) {
+    LiveInterval::Segment *Segment = LR->getSegmentContaining(Start);
+    if (!Segment || Segment->valno != VNI) {
+      if (Kills)
+        Kills->push_back(Start);
+      return;
     }
+    if (Segment->end < Stop)
+      Stop = Segment->end, ToEnd = false;
+  }
 
-    // Limited by the next def.
-    if (I.valid() && I.start() < Stop)
-      Stop = I.start(), ToEnd = false;
-    // Limited by VNI's live range.
-    else if (!ToEnd && Kills)
-      Kills->push_back(Stop);
+  // There could already be a short def at Start.
+  if (I.valid() && I.start() <= Start) {
+    // Stop when meeting a different location or an already extended interval.
+    Start = Start.getNextSlot();
+    if (I.value() != LocNo || I.stop() != Start)
+      return;
+    // This is a one-slot placeholder. Just skip it.
+    ++I;
+  }
 
-    if (Start >= Stop)
-      continue;
+  // Limited by the next def.
+  if (I.valid() && I.start() < Stop)
+    Stop = I.start(), ToEnd = false;
+  // Limited by VNI's live range.
+  else if (!ToEnd && Kills)
+    Kills->push_back(Stop);
 
+  if (Start < Stop)
     I.insert(Start, Stop, LocNo);
-
-    // If we extended to the MBB end, propagate down the dominator tree.
-    if (!ToEnd)
-      continue;
-    const std::vector<MachineDomTreeNode*> &Children =
-      MDT.getNode(MBB)->getChildren();
-    for (unsigned i = 0, e = Children.size(); i != e; ++i) {
-      MachineBasicBlock *MBB = Children[i]->getBlock();
-      if (UVS.dominates(MBB))
-        Todo.push_back(LIS.getMBBStartIdx(MBB));
-    }
-  } while (!Todo.empty());
 }
 
 void