[PATCH] D26359: Better handling of values missing in predecessors

[Krzysztof Parzyszek via llvm-commits]

kparzysz retitled this revision from "Don't assert on missing value from predecessor" to "Better handling of values missing in predecessors".
kparzysz updated the summary for this revision.
kparzysz updated this revision to Diff 78526.
kparzysz added a comment.

Changed VNI to PVNI to avoid warnings about unused variable in release builds (VNI and PVNI are equal at that point).

Updated the summary and title.


Repository:
  rL LLVM

https://reviews.llvm.org/D26359

Files:
  lib/CodeGen/LiveIntervalAnalysis.cpp
  lib/CodeGen/SplitKit.cpp
  lib/CodeGen/SplitKit.h


Index: lib/CodeGen/SplitKit.h
===================================================================
--- lib/CodeGen/SplitKit.h
+++ lib/CodeGen/SplitKit.h
@@ -386,10 +386,14 @@
   /// Return true if any ranges were skipped.
   bool transferValues();
 
-  /// Live range @p LR has a live PHI def at the beginning of block @p B.
-  /// Extend the range @p LR of all predecessor values that reach this def.
+  /// Live range @p LR corresponding to the lane Mask @p LM has a live
+  /// PHI def at the beginning of block @p B. Extend the range @p LR of
+  /// all predecessor values that reach this def. If @p LR is a subrange,
+  /// the array @p Undefs is the set of all locations where it is undefined
+  /// via <def,read-undef> in other subranges for the same register.
   void extendPHIRange(MachineBasicBlock &B, LiveRangeCalc &LRC,
-                      LiveRange &LR, ArrayRef<SlotIndex>);
+                      LiveRange &LR, LaneBitmask LM,
+                      ArrayRef<SlotIndex> Undefs);
 
   /// extendPHIKillRanges - Extend the ranges of all values killed by original
   /// parent PHIDefs.
Index: lib/CodeGen/SplitKit.cpp
===================================================================
--- lib/CodeGen/SplitKit.cpp
+++ lib/CodeGen/SplitKit.cpp
@@ -1092,13 +1092,19 @@
 }
 
 void SplitEditor::extendPHIRange(MachineBasicBlock &B, LiveRangeCalc &LRC,
-                                 LiveRange &LR, ArrayRef<SlotIndex> Undefs) {
+                                 LiveRange &LR, LaneBitmask LM,
+                                 ArrayRef<SlotIndex> Undefs) {
   for (MachineBasicBlock *P : B.predecessors()) {
     SlotIndex End = LIS.getMBBEndIdx(P);
     SlotIndex LastUse = End.getPrevSlot();
     // The predecessor may not have a live-out value. That is OK, like an
     // undef PHI operand.
-    if (Edit->getParent().liveAt(LastUse))
+    LiveInterval &PLI = Edit->getParent();
+    // Need the cast because the inputs to ?: would otherwise be deemed
+    // "incompatible": SubRange vs LiveInterval.
+    LiveRange &PSR = (LM != ~0u) ? getSubRangeForMask(LM, PLI)
+                                 : static_cast<LiveRange&>(PLI);
+    if (PSR.liveAt(LastUse))
       LRC.extend(LR, End, /*PhysReg=*/0, Undefs);
   }
 }
@@ -1120,7 +1126,7 @@
     LiveRangeCalc &LRC = getLRCalc(RegIdx);
     MachineBasicBlock &B = *LIS.getMBBFromIndex(V->def);
     if (!removeDeadSegment(V->def, LI))
-      extendPHIRange(B, LRC, LI, /*Undefs=*/{});
+      extendPHIRange(B, LRC, LI, ~0u, /*Undefs=*/{});
   }
 
   SmallVector<SlotIndex, 4> Undefs;
@@ -1141,7 +1147,7 @@
                    &LIS.getVNInfoAllocator());
       Undefs.clear();
       LI.computeSubRangeUndefs(Undefs, PS.LaneMask, MRI, *LIS.getSlotIndexes());
-      extendPHIRange(B, SubLRC, S, Undefs);
+      extendPHIRange(B, SubLRC, S, PS.LaneMask, Undefs);
     }
   }
 }
Index: lib/CodeGen/LiveIntervalAnalysis.cpp
===================================================================
--- lib/CodeGen/LiveIntervalAnalysis.cpp
+++ lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -388,9 +388,11 @@
       if (!LiveOut.insert(Pred).second)
         continue;
       SlotIndex Stop = Indexes.getMBBEndIdx(Pred);
-      assert(OldRange.getVNInfoBefore(Stop) == VNI &&
-             "Wrong value out of predecessor");
-      WorkList.push_back(std::make_pair(Stop, VNI));
+      // The exit from a predecessor may be jointly dominated by undefs.
+      if (VNInfo *PVNI = OldRange.getVNInfoBefore(Stop)) {
+        assert(PVNI == VNI && "Wrong value out of predecessor");
+        WorkList.push_back(std::make_pair(Stop, PVNI));
+      }
     }
   }
 }


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