[compiler-rt] [scudo] Avoid splitting aligned allocations on Trusty (PR #69281)

[via llvm-commits]

================
@@ -122,7 +122,30 @@ bool mapSecondary(const Options &Options, uptr CommitBase, uptr CommitSize,
   Flags |= MAP_RESIZABLE;
   Flags |= MAP_ALLOWNOMEM;
 
-  const uptr MaxUnusedCacheBytes = MaxUnusedCachePages * getPageSizeCached();
+  const uptr PageSize = getPageSizeCached();
+  if (SCUDO_TRUSTY) {
+    /*
+     * On Trusty we need AllocPos to be usable for shared memory, which cannot
+     * cross multiple mappings. This means we need to split around AllocPos
+     * and not over it. We can only do this if the address is page-aligned.
+     */
+    const uptr TaggedSize = AllocPos - CommitBase;
+    if (useMemoryTagging<Config>(Options) && isAligned(TaggedSize, PageSize)) {
+      DCHECK_NE(TaggedSize, 0);
+      DCHECK_LT(TaggedSize, CommitSize);
----------------
ChiaHungDuan wrote:

This is redundant.

https://github.com/llvm/llvm-project/pull/69281