[compiler-rt] [TSan] Fix p == end == ShadowMem::end in ShadowSet (PR #144994)

[Thurston Dang via llvm-commits]

================
@@ -577,7 +578,8 @@ static void MemoryRangeSet(uptr addr, uptr size, RawShadow val) {
       Die();
   }
   // Set the ending.
-  ShadowSet(mid2, end, val);
+  if (mid2 < end)
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thurstond wrote:

IIUC the only case this is not true is if `mid2 == end`? If so, please DHECK that in the else condition (to guard against something totally unexpected happening i.e., mid2 > end, which would silently omit ShadowSet).

https://github.com/llvm/llvm-project/pull/144994