[scudo] Fix implicitly narrow casting (NFC)

[Chia-hungDuan]

Summary

u16 may be promoted to int by arithmetic type conversion. Do an explicit
cast to avoid certain compiler's warning. This fixes the problem
introduced by 0fb2aeef5310eaba2915b30810464a744a80da15

[PeteSteinfeld]

@Chia-hungDuan, I was experiencing similar problems building that @dyung was with your original patch. I was able to successfully build this patch in my environment, though. If @kamaub is happy with it, I think you're good to go.

[Chia-hungDuan]

In D135985#3859683, @PeteSteinfeld wrote:

@Chia-hungDuan, I was experiencing similar problems building that @dyung was with your original patch. I was able to successfully build this patch in my environment, though. If @kamaub is happy with it, I think you're good to go.

Thanks! I'll wait for @kamaub's approval.

[dyung]

Just wanted to add that I was also able to successfully build with this patch.

[Chia-hungDuan]

In D135985#3859713, @dyung wrote:

Just wanted to add that I was also able to successfully build with this patch.

Thank you @dyung!

[PeteSteinfeld]

@Chia-hungDuan, I cannot currently build my product. Merging this patch will solve that problem. Of course, it's possible that after merging, @kamaub will still have intermittent test failures in his product, but at least he'll be able to build his product so that he can analyze his problems.

Thus, I urge you to merge this patch, which I've already verified will fix the build problems.

[Chia-hungDuan]

In D135985#3860272, @PeteSteinfeld wrote:

@Chia-hungDuan, I cannot currently build my product. Merging this patch will solve that problem. Of course, it's possible that after merging, @kamaub will still have intermittent test failures in his product, but at least he'll be able to build his product so that he can analyze his problems.

Thus, I urge you to merge this patch, which I've already verified will fix the build problems.

Ok, let me do it now

compiler-rt/lib/scudo/standalone/local_cache.h

ALWAYS_INLINE void initCacheMaybe(PerClass *C) {
     initCache();
     DCHECK_NE(C->MaxCount, 0U);
   }
 
   NOINLINE void initCache() {
     for (uptr I = 0; I < NumClasses; I++) {
       PerClass *P = &PerClassArray[I];
       const uptr Size = SizeClassAllocator::getSizeByClassId(I);
-      P->MaxCount = 2 * TransferBatch::getMaxCached(Size);
+      P->MaxCount = static_cast<u16>(2 * TransferBatch::getMaxCached(Size));
       if (I != BatchClassId) {
         P->ClassSize = Size;
       } else {
         // ClassSize in this struct is only used for malloc/free stats, which
         // should only track user allocations, not internal movements.
         P->ClassSize = 0;
       }
     }
private:
 
   NOINLINE void drain(PerClass *C, uptr ClassId) {
     const u16 Count = Min(static_cast<u16>(C->MaxCount / 2), C->Count);
     TransferBatch *B =
         createBatch(ClassId, Allocator->decompactPtr(ClassId, C->Chunks[0]));
     if (UNLIKELY(!B))
       reportOutOfMemory(SizeClassAllocator::getSizeByClassId(BatchClassId));
     B->setFromArray(&C->Chunks[0], Count);
-    C->Count -= Count;
-    for (uptr I = 0; I < C->Count; I++)
+    // u16 will be promoted to int by arithmetic type conversion.
+    C->Count = static_cast<u16>(C->Count - Count);
+    for (u16 I = 0; I < C->Count; I++)
       C->Chunks[I] = C->Chunks[I + Count];
     Allocator->pushBatch(ClassId, B);
   }
 };
 
 } // namespace scudo
 
 #endif // SCUDO_LOCAL_CACHE_H_