[SCEV] Temporarily disable loop versioning for the purpose

of turning SCEVUnknowns of PHIs into AddRecExprs.

This feature is now hidden behind the -scev-version-unknown flag.

Fixes PR36032 and PR35432.

llvm-svn: 325687

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 279417cb1ab..3406c4c7a04 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -205,6 +205,11 @@ static cl::opt<unsigned>
                   cl::desc("Max coefficients in AddRec during evolving"),
                   cl::init(16));
 
+static cl::opt<bool> VersionUnknown(
+    "scev-version-unknown", cl::Hidden,
+    cl::desc("Use predicated scalar evolution to version SCEVUnknowns"),
+    cl::init(false));
+
 //===----------------------------------------------------------------------===//
 //                           SCEV class definitions
 //===----------------------------------------------------------------------===//
@@ -11573,6 +11578,8 @@ private:
   // couldn't create an AddRec for it, or couldn't add the predicate), we just
   // return \p Expr.
   const SCEV *convertToAddRecWithPreds(const SCEVUnknown *Expr) {
+    if (!VersionUnknown)
+      return Expr;
     if (!isa<PHINode>(Expr->getValue()))
       return Expr;
     Optional<std::pair<const SCEV *, SmallVector<const SCEVPredicate *, 3>>>