[SCEV] Have getRangeForAffineARHelper take StartRange by const reference to avoid a copy in many of the cases.

llvm-svn: 302398
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 7facf36..b1ab656 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4842,7 +4842,7 @@
 // from StartRange and then is changed by Step up to MaxBECount times. Signed
 // argument defines if we treat Step as signed or unsigned.
 static ConstantRange getRangeForAffineARHelper(APInt Step,
-                                               ConstantRange StartRange,
+                                               const ConstantRange &StartRange,
                                                const APInt &MaxBECount,
                                                unsigned BitWidth, bool Signed) {
   // If either Step or MaxBECount is 0, then the expression won't change, and we