Make sure the whole live range is covered when values are pruned twice.

JoinVals::pruneValues() calls LIS->pruneValue() to avoid conflicts when
overlapping two different values. This produces a set of live range end
points that are used to reconstruct the live range (with SSA update)
after joining the two registers.

When a value is pruned twice, the set of end points was insufficient:

  v1 = DEF
  v1 = REPLACE1
  v1 = REPLACE2
  KILL v1

The end point at KILL would only reconstruct the live range from
REPLACE2 to KILL, leaving the range REPLACE1-REPLACE2 dead.

Add REPLACE2 as an end point in this case so the full live range is
reconstructed.

This fixes PR13999.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165056 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 1 deletions

diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp
index f45072f1ac..ad1f5f4f12 100644
--- a/lib/CodeGen/RegisterCoalescer.cpp
+++ b/lib/CodeGen/RegisterCoalescer.cpp
@@ -1733,11 +1733,15 @@ void JoinVals::pruneValues(JoinVals &Other,
       // This value takes precedence over the value in Other.LI.
       LIS->pruneValue(&Other.LI, Def, &EndPoints);
       // Remove <def,read-undef> flags. This def is now a partial redef.
-      if (!Def.isBlock())
+      if (!Def.isBlock()) {
         for (MIOperands MO(Indexes->getInstructionFromIndex(Def));
              MO.isValid(); ++MO)
           if (MO->isReg() && MO->isDef() && MO->getReg() == LI.reg)
             MO->setIsUndef(false);
+	// This value will reach instructions below, but we need to make sure
+	// the live range also reaches the instruction at Def.
+	EndPoints.push_back(Def);
+      }
       DEBUG(dbgs() << "\t\tpruned " << PrintReg(Other.LI.reg) << " at " << Def
                    << ": " << Other.LI << '\n');
       break;