[IndVarSimplify][SimplifyIndVar] Move WidenIV to Utils/SimplifyIndVar. NFCI.

This moves WidenIV from IndVarSimplify to Utils/SimplifyIndVar so that we have
createWideIV available as a generic helper utility. I.e., this is not only
useful in IndVarSimplify, but could be useful for loop transformations. For
example, motivation for this refactoring is the loop flatten transformation: if
induction variables in a loop nest can be widened, we can avoid having to
perform certain overflow checks, enabling this transformation.

Differential Revision: https://reviews.llvm.org/D90421

include/llvm/Transforms/Utils/SimplifyIndVar.h

@@ -15,6 +15,8 @@
 #ifndef LLVM_TRANSFORMS_UTILS_SIMPLIFYINDVAR_H
 #define LLVM_TRANSFORMS_UTILS_SIMPLIFYINDVAR_H
 
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/ValueHandle.h"
 
 namespace llvm {
@@ -57,6 +59,27 @@ bool simplifyLoopIVs(Loop *L, ScalarEvolution *SE, DominatorTree *DT,
                      LoopInfo *LI, const TargetTransformInfo *TTI,
                      SmallVectorImpl<WeakTrackingVH> &Dead);
 
+/// Collect information about induction variables that are used by sign/zero
+/// extend operations. This information is recorded by CollectExtend and provides
+/// the input to WidenIV.
+struct WideIVInfo {
+  PHINode *NarrowIV = nullptr;
+
+  // Widest integer type created [sz]ext
+  Type *WidestNativeType = nullptr;
+
+  // Was a sext user seen before a zext?
+  bool IsSigned = false;
+};
+
+/// Widen Induction Variables - Extend the width of an IV to cover its
+/// widest uses.
+PHINode *createWideIV(WideIVInfo &WI,
+    LoopInfo *LI, ScalarEvolution *SE, SCEVExpander &Rewriter,
+    DominatorTree *DT, SmallVectorImpl<WeakTrackingVH> &DeadInsts,
+    unsigned &NumElimExt, unsigned &NumWidened,
+    bool HasGuards, bool UsePostIncrementRanges);
+
 } // end namespace llvm
 
 #endif // LLVM_TRANSFORMS_UTILS_SIMPLIFYINDVAR_H