[LLVM][ADT] Explicitly convert size_t values to SmallVector's size type (#77939)

Multiple places rely on implicit conversion when assigning 'size_t'
values to the member fields (size or capacity) of SmallVector.

Depending on the platform / compiler configuration, this may result in
narrowing conversion warnings (especially given that the size type of
SmallVector's member fields is determined based on type T - in
SmallVector<T>). To avoid the problem altogether, make the conversions
explicit.

Co-authored-by: Orest Chura <[email protected]>

Author: andrey-golubev

llvm/include/llvm/ADT/SmallVector.h

@@ -61,7 +61,7 @@ template <class Size_T> class SmallVectorBase {
 
   SmallVectorBase() = delete;
   SmallVectorBase(void *FirstEl, size_t TotalCapacity)
-      : BeginX(FirstEl), Capacity(TotalCapacity) {}
+      : BeginX(FirstEl), Capacity(static_cast<Size_T>(TotalCapacity)) {}
 
   /// This is a helper for \a grow() that's out of line to reduce code
   /// duplication.  This function will report a fatal error if it can't grow at
@@ -99,8 +99,18 @@ template <class Size_T> class SmallVectorBase {
   ///
   /// This does not construct or destroy any elements in the vector.
   void set_size(size_t N) {
-    assert(N <= capacity());
-    Size = N;
+    assert(N <= capacity()); // implies no overflow in assignment
+    Size = static_cast<Size_T>(N);
+  }
+
+  /// Set the array data pointer to \p Begin and capacity to \p N.
+  ///
+  /// This does not construct or destroy any elements in the vector.
+  //  This does not clean up any existing allocation.
+  void set_allocation_range(void *Begin, size_t N) {
+    assert(N <= SizeTypeMax());
+    BeginX = Begin;
+    Capacity = static_cast<Size_T>(N);
   }
 };
 
@@ -467,8 +477,7 @@ void SmallVectorTemplateBase<T, TriviallyCopyable>::takeAllocationForGrow(
   if (!this->isSmall())
     free(this->begin());
 
-  this->BeginX = NewElts;
-  this->Capacity = NewCapacity;
+  this->set_allocation_range(NewElts, NewCapacity);
 }
 
 /// SmallVectorTemplateBase<TriviallyCopyable = true> - This is where we put

llvm/lib/Support/SmallVector.cpp

@@ -153,8 +153,7 @@ void SmallVectorBase<Size_T>::grow_pod(void *FirstEl, size_t MinSize,
       NewElts = replaceAllocation(NewElts, TSize, NewCapacity, size());
   }
 
-  this->BeginX = NewElts;
-  this->Capacity = NewCapacity;
+  this->set_allocation_range(NewElts, NewCapacity);
 }
 
 template class llvm::SmallVectorBase<uint32_t>;