[SLP][REVEC] Add an option to control SLP revectorization. NFC.

Author: HanKuanChen

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -113,6 +113,10 @@ static cl::opt<bool>
     RunSLPVectorization("vectorize-slp", cl::init(true), cl::Hidden,
                         cl::desc("Run the SLP vectorization passes"));
 
+static cl::opt<bool>
+    SLPReVec("slp-revec", cl::init(false), cl::Hidden,
+             cl::desc("Enable vectorization for wider vector utilization"));
+
 static cl::opt<int>
     SLPCostThreshold("slp-threshold", cl::init(0), cl::Hidden,
                      cl::desc("Only vectorize if you gain more than this "