[LoopVersioning] Relax an assert for LCSSA PHIs

When you have multiple LCSSA (single-operand) PHIs that are converted
into two-operand PHIs due to versioning, only assert that the PHI
currently being converted has a single operand.  I.e. we don't want to
check PHIs that were converted earlier in the loop.

Fixes PR27023.

Thanks to Karl-Johan Karlsson for the minimized testcase!

llvm-svn: 264081

1 files changed, 4 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopVersioning.cpp b/llvm/lib/Transforms/Utils/LoopVersioning.cpp
index 19c7fa7..e3f711f 100644
--- a/llvm/lib/Transforms/Utils/LoopVersioning.cpp
+++ b/llvm/lib/Transforms/Utils/LoopVersioning.cpp
@@ -133,10 +133,11 @@ void LoopVersioning::addPHINodes(
     // First see if we have a single-operand PHI with the value defined by the
     // original loop.
     for (auto I = PHIBlock->begin(); (PN = dyn_cast<PHINode>(I)); ++I) {
-      assert(PN->getNumOperands() == 1 &&
-             "Exit block should only have on predecessor");
-      if (PN->getIncomingValue(0) == Inst)
+      if (PN->getIncomingValue(0) == Inst) {
+        assert(PN->getNumOperands() == 1 &&
+               "Exit block should only have on predecessor");
         break;
+      }
     }
     // If not create it.
     if (!PN) {