LiveIntervalAnalysis: Rework constructMainRangeFromSubranges()

We now use LiveRangeCalc::extendToUses() instead of a specially designed
algorithm in constructMainRangeFromSubranges():
- The original motivation for constructMainRangeFromSubranges() were
  differences between the main liverange and subranges because of hidden
  dead definitions. This case however cannot happen anymore with the
  DetectDeadLaneMasks pass in place.
- It simplifies the code.
- This fixes a longstanding bug where we did not properly create new SSA
  values on merging control flow (the MachineVerifier missed most of
  these cases).
- Move constructMainRangeFromSubranges() to LiveIntervalAnalysis and
  LiveRangeCalc to better match the implementation/available helper
  functions.

This re-applies r269016. The fixes from r270290 and r270259 should avoid
the machine verifier problems this time.

llvm-svn: 270291

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/LiveRangeCalc.h b/llvm/lib/CodeGen/LiveRangeCalc.h
index ff38c68820f..9de48b72288 100644
--- a/llvm/lib/CodeGen/LiveRangeCalc.h
+++ b/llvm/lib/CodeGen/LiveRangeCalc.h
@@ -189,6 +189,11 @@ public:
   /// enabled.
   void calculate(LiveInterval &LI, bool TrackSubRegs);
 
+  /// For live interval \p LI with correct SubRanges construct matching
+  /// information for the main live range. Expects the main live range to not
+  /// have any segments or value numbers.
+  void constructMainRangeFromSubranges(LiveInterval &LI);
+
   //===--------------------------------------------------------------------===//
   // Low-level interface.
   //===--------------------------------------------------------------------===//