[RuntimeUnrolling] Populate the VMap entry correctly when default generated through lookup

During runtime unrolling on loops with multiple exits, we update the
exit blocks with the correct phi values from both original and remainder
loop.
In this process, we lookup the VMap for the mapped incoming phi values,
but did not update the VMap if a default entry was generated in the VMap
during the lookup. This default value is generated when constants or
values outside the current loop are looked up.
This patch fixes the assertion failure when null entries are present in
the VMap because of this lookup. Added a testcase that showcases the
problem.

llvm-svn: 313358

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp b/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
index 01c9362e4a4..c03fa153678 100644
--- a/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -782,11 +782,15 @@ bool llvm::UnrollRuntimeLoopRemainder(Loop *L, unsigned Count,
      // Add the incoming values from the remainder code to the end of the phi
      // node.
      for (unsigned i =0; i < oldNumOperands; i++){
-       Value *newVal = VMap[Phi->getIncomingValue(i)];
+       Value *newVal = VMap.lookup(Phi->getIncomingValue(i));
        // newVal can be a constant or derived from values outside the loop, and
-       // hence need not have a VMap value.
-       if (!newVal)
+       // hence need not have a VMap value. Also, since lookup already generated
+       // a default "null" VMap entry for this value, we need to populate that
+       // VMap entry correctly, with the mapped entry being itself.
+       if (!newVal) {
          newVal = Phi->getIncomingValue(i);
+         VMap[Phi->getIncomingValue(i)] = Phi->getIncomingValue(i);
+       }
        Phi->addIncoming(newVal,
                            cast<BasicBlock>(VMap[Phi->getIncomingBlock(i)]));
      }