[PATCH] D26359: Don't assert on missing value from predecessor

[Krzysztof Parzyszek via llvm-commits]

kparzysz created this revision.
kparzysz added a reviewer: MatzeB.
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kparzysz set the repository for this revision to rL LLVM.

The function extendSegmentsToUses will assert if it encounters a value that is live-in to a block BB, but in some predecessor that value is either not live-on-exit, or differs from the expected one.
Since uses need to be jointly dominated by the union of defs and undefs, it may happen that the exit from one or more predecessors will be jointly dominated only by undefs. In such case, the value will not be live-on-exit from that block.

Limit the assertion to cases when the value does exist in a predecessor, but is not what is expected.


Repository:
  rL LLVM

https://reviews.llvm.org/D26359

Files:
  lib/CodeGen/LiveIntervalAnalysis.cpp


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, VNI));
+      }
     }
   }
 }


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