[NFC] Add size inference to to_vector

A default calculated size for SmallVector was added in
https://reviews.llvm.org/D92522 after discussion in
https://groups.google.com/g/llvm-dev/c/Z-VwNCTRGSg, but to_vector still
requires an explicit size. This patch adds the default size to to_vector
as well, so that this case doesn't unnecessarily force users to pick an
arbitrary size.

Reviewed By: silvas, dblaikie

Differential Revision: https://reviews.llvm.org/D112968

Author: GMNGeoffrey

llvm/include/llvm/ADT/SmallVector.h

@@ -1239,13 +1239,22 @@ inline size_t capacity_in_bytes(const SmallVector<T, N> &X) {
   return X.capacity_in_bytes();
 }
 
+template <typename RangeType>
+using ValueTypeFromRangeType =
+    typename std::remove_const<typename std::remove_reference<
+        decltype(*std::begin(std::declval<RangeType &>()))>::type>::type;
+
 /// Given a range of type R, iterate the entire range and return a
 /// SmallVector with elements of the vector.  This is useful, for example,
 /// when you want to iterate a range and then sort the results.
 template <unsigned Size, typename R>
-SmallVector<typename std::remove_const<typename std::remove_reference<
-                decltype(*std::begin(std::declval<R &>()))>::type>::type,
-            Size>
+SmallVector<ValueTypeFromRangeType<R>, Size> to_vector(R &&Range) {
+  return {std::begin(Range), std::end(Range)};
+}
+template <typename R>
+SmallVector<ValueTypeFromRangeType<R>,
+            CalculateSmallVectorDefaultInlinedElements<
+                ValueTypeFromRangeType<R>>::value>
 to_vector(R &&Range) {
   return {std::begin(Range), std::end(Range)};
 }

llvm/unittests/ADT/STLExtrasTest.cpp

@@ -307,6 +307,13 @@ TEST(STLExtrasTest, ToVector) {
     EXPECT_EQ(I, Enumerated[I].index());
     EXPECT_EQ(v[I], Enumerated[I].value());
   }
+
+  auto EnumeratedImplicitSize = to_vector(enumerate(v));
+  ASSERT_EQ(3u, EnumeratedImplicitSize.size());
+  for (size_t I = 0; I < v.size(); ++I) {
+    EXPECT_EQ(I, EnumeratedImplicitSize[I].index());
+    EXPECT_EQ(v[I], EnumeratedImplicitSize[I].value());
+  }
 }
 
 TEST(STLExtrasTest, ConcatRange) {