Automerge: [TSan] Fix p == end == ShadowMem::end in ShadowSet (#144994)

In `ShadowSet`, when `p == end == ShadowMem::end`, it triggered an
assertion fail previously.

Now we do not allow `p == end` anymore in `ShadowSet`.

Author: Camsyn

compiler-rt/lib/tsan/rtl/tsan_rtl_access.cpp

@@ -523,9 +523,9 @@ ALWAYS_INLINE USED void UnalignedMemoryAccess(ThreadState* thr, uptr pc,
 }
 
 void ShadowSet(RawShadow* p, RawShadow* end, RawShadow v) {
-  DCHECK_LE(p, end);
+  DCHECK_LT(p, end);
   DCHECK(IsShadowMem(p));
-  DCHECK(p == end || IsShadowMem(end - 1));
+  DCHECK(IsShadowMem(end - 1));
   UNUSED const uptr kAlign = kShadowCnt * kShadowSize;
   DCHECK_EQ(reinterpret_cast<uptr>(p) % kAlign, 0);
   DCHECK_EQ(reinterpret_cast<uptr>(end) % kAlign, 0);
@@ -569,6 +569,7 @@ static void MemoryRangeSet(uptr addr, uptr size, RawShadow val) {
   RawShadow* mid1 =
       Min(end, reinterpret_cast<RawShadow*>(RoundUp(
                    reinterpret_cast<uptr>(begin) + kPageSize / 2, kPageSize)));
+  // begin must < mid1
   ShadowSet(begin, mid1, val);
   // Reset middle part.
   RawShadow* mid2 = RoundDown(end, kPageSize);
@@ -577,7 +578,10 @@ static void MemoryRangeSet(uptr addr, uptr size, RawShadow val) {
       Die();
   }
   // Set the ending.
-  ShadowSet(mid2, end, val);
+  if (mid2 < end)
+    ShadowSet(mid2, end, val);
+  else
+    DCHECK_EQ(mid2, end);
 }
 
 void MemoryResetRange(ThreadState* thr, uptr pc, uptr addr, uptr size) {