Treat segment [B, E) as not overlapping block with boundaries [A, B)

llvm-svn: 292446

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/LiveRangeCalc.cpp b/llvm/lib/CodeGen/LiveRangeCalc.cpp
index fd22c404871..e2ae7c0a0c9 100644
--- a/llvm/lib/CodeGen/LiveRangeCalc.cpp
+++ b/llvm/lib/CodeGen/LiveRangeCalc.cpp
@@ -310,7 +310,12 @@ bool LiveRangeCalc::isDefOnEntry(LiveRange &LR, ArrayRef<SlotIndex> Undefs,
       return MarkDefined(B);
     SlotIndex Begin, End;
     std::tie(Begin, End) = Indexes->getMBBRange(&B);
-    LiveRange::iterator UB = std::upper_bound(LR.begin(), LR.end(), End);
+    // Treat End as not belonging to B.
+    // If LR has a segment S that starts at the next block, i.e. [End, ...),
+    // std::upper_bound will return the segment following S. Instead,
+    // S should be treated as the first segment that does not overlap B.
+    LiveRange::iterator UB = std::upper_bound(LR.begin(), LR.end(),
+                                              End.getPrevSlot());
     if (UB != LR.begin()) {
       LiveRange::Segment &Seg = *std::prev(UB);
       if (Seg.end > Begin) {