[compiler-rt] [scudo] Add config option to modify get usable size behavior (PR #158710)

[via llvm-commits]

================
@@ -706,19 +706,24 @@ class Allocator {
         if (!getChunkFromBlock(Block, &Chunk, &Header) &&
             !getChunkFromBlock(addHeaderTag(Block), &Chunk, &Header))
           return;
-      } else {
-        if (!getChunkFromBlock(addHeaderTag(Block), &Chunk, &Header))
-          return;
-      }
-      if (Header.State == Chunk::State::Allocated) {
-        uptr TaggedChunk = Chunk;
-        if (allocatorSupportsMemoryTagging<AllocatorConfig>())
-          TaggedChunk = untagPointer(TaggedChunk);
-        if (useMemoryTagging<AllocatorConfig>(Primary.Options.load()))
-          TaggedChunk = loadTag(Chunk);
-        Callback(TaggedChunk, getSize(reinterpret_cast<void *>(Chunk), &Header),
-                 Arg);
-      }
+      } else if (!getChunkFromBlock(addHeaderTag(Block), &Chunk, &Header))
+        return;
+
+      if (Header.State != Chunk::State::Allocated)
+        return;
+
+      uptr TaggedChunk = Chunk;
+      if (allocatorSupportsMemoryTagging<AllocatorConfig>())
+        TaggedChunk = untagPointer(TaggedChunk);
+      uptr Size;
+      if (UNLIKELY(useMemoryTagging<AllocatorConfig>(Primary.Options.load()))) {
+        TaggedChunk = loadTag(Chunk);
+        Size = getSize(reinterpret_cast<void *>(Chunk), &Header);
+      } else if (AllocatorConfig::getExactUsableSize())
+        Size = getSize(reinterpret_cast<void *>(Chunk), &Header);
+      else
+        Size = getUsableSize(reinterpret_cast<void *>(Chunk), &Header);
----------------
ChiaHungDuan wrote:

```suggestion
      } else if (AllocatorConfig::getExactUsableSize()) {
        Size = getSize(reinterpret_cast<void *>(Chunk), &Header);
      } else {
        Size = getUsableSize(reinterpret_cast<void *>(Chunk), &Header);
      }
```

https://github.com/llvm/llvm-project/pull/158710