[SCEV][NFC] Introduce utility function to get power of 2

The new function has been added to SCEV that allows to raise the number 2
to the desired power.

Authored-by: Dmitry Bakunevich

Differential Revision: https://reviews.llvm.org/D144381

Author: dbakunevich

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -655,6 +655,12 @@ class ScalarEvolution {
   /// Return a SCEV for the constant 1 of a specific type.
   const SCEV *getOne(Type *Ty) { return getConstant(Ty, 1); }
 
+  /// Return a SCEV for the constant \p Power of two.
+  const SCEV *getPowerOfTwo(Type *Ty, unsigned Power) {
+    assert(Power < getTypeSizeInBits(Ty) && "Power out of range");
+    return getConstant(APInt::getOneBitSet(getTypeSizeInBits(Ty), Power));
+  }
+
   /// Return a SCEV for the constant -1 of a specific type.
   const SCEV *getMinusOne(Type *Ty) {
     return getConstant(Ty, -1, /*isSigned=*/true);

llvm/unittests/Analysis/ScalarEvolutionTest.cpp

@@ -1744,4 +1744,20 @@ TEST_F(ScalarEvolutionsTest, ComputeMaxTripCountFromMultiDemArray) {
   });
 }
 
+TEST_F(ScalarEvolutionsTest, CheckGetPowerOfTwo) {
+  Module M("CheckGetPowerOfTwo", Context);
+  FunctionType *FTy = FunctionType::get(Type::getVoidTy(Context), {}, false);
+  Function *F = Function::Create(FTy, Function::ExternalLinkage, "foo", M);
+  BasicBlock *Entry = BasicBlock::Create(Context, "entry", F);
+  IRBuilder<> Builder(Entry);
+  Builder.CreateRetVoid();
+  ScalarEvolution SE = buildSE(*F);
+
+  for (unsigned short i = 0; i < 64; ++i)
+    EXPECT_TRUE(
+        dyn_cast<SCEVConstant>(SE.getPowerOfTwo(Type::getInt64Ty(Context), i))
+            ->getValue()
+            ->equalsInt(1ULL << i));
+}
+
 }  // end namespace llvm