[ADT] Fix SmallVector unused template instantiation on 32-bit systems.

[browneee]

Summary

This was introduced in dda3c19a3618dce94 aka D77621.

The unused template instantiation causes a warning on 32 bit systems
about truncating a uint64_t to 32-bit size_t.

[dblaikie]

Looks good - thanks!

[smeenai]

llvm/lib/Support/SmallVector.cpp

86

Wouldn't hurt to include stdint.h explicitly in this file, to ensure these constants are available.

[dblaikie]

llvm/lib/Support/SmallVector.cpp

86

Sorry I didn't catch this - @browneee Could you commit this in a follow-up (no need to send it for review)?

[browneee]

llvm/lib/Support/SmallVector.cpp

86

Done:
https://github.com/llvm/llvm-project/commit/a1bd5cd539f9e2fd34e522b848e751342985e882

Sorry I missed your comment smeenai. I didn't realize how phabricator shows approved with still open comments.

llvm/lib/Support/SmallVector.cpp

if (BeginX == FirstEl) {
     NewElts = safe_realloc(this->BeginX, NewCapacity * TSize);
   }
 
   this->BeginX = NewElts;
   this->Capacity = NewCapacity;
 }
 
 template class llvm::SmallVectorBase<uint32_t>;
+
+// Disable the uint64_t instantiation for 32-bit builds.
+// Both uint32_t and uint64_t instantations are needed for 64-bit builds.
+// This instantiation will never be used in 32-bit builds, and will cause
+// warnings when sizeof(Size_T) > sizeof(size_t).
+#if SIZE_MAX > UINT32_MAX
 template class llvm::SmallVectorBase<uint64_t>;
+
+// Assertions to ensure this #if stays in sync with SmallVectorSizeType.
+static_assert(sizeof(SmallVectorSizeType<char>) == sizeof(uint64_t),
+              "Expected SmallVectorBase<uint64_t> variant to be in use.");
+#else
+static_assert(sizeof(SmallVectorSizeType<char>) == sizeof(uint32_t),
+              "Expected SmallVectorBase<uint32_t> variant to be in use.");
+#endif