Fix ScalarEvolution's "exhaustive" trip count evaluation code to avoid

assuming that loops are in canonical form, as ScalarEvolution doesn't
depend on LoopSimplify itself. Also, with indirectbr not all loops can
be simplified. This fixes PR7416.

llvm-svn: 106389

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 7e7fc756d10..251b57a0f98 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4238,8 +4238,11 @@ ScalarEvolution::ComputeBackedgeTakenCountExhaustively(const Loop *L,
   PHINode *PN = getConstantEvolvingPHI(Cond, L);
   if (PN == 0) return getCouldNotCompute();
 
-  // Since the loop is canonicalized, the PHI node must have two entries.  One
-  // entry must be a constant (coming in from outside of the loop), and the
+  // If the loop is canonicalized, the PHI will have exactly two entries.
+  // That's the only form we support here.
+  if (PN->getNumIncomingValues() != 2) return getCouldNotCompute();
+
+  // One entry must be a constant (coming in from outside of the loop), and the
   // second must be derived from the same PHI.
   bool SecondIsBackedge = L->contains(PN->getIncomingBlock(1));
   Constant *StartCST =