[analyzer] CStringChecker.cpp: Remove the duplicated check about null dereference on dest-buffer or src-buffer.

[MTC]

Summary

CheckBufferAccess() calls CheckNonNull(), so there are some calls to CheckNonNull() that are useless.

[NoQ]

Making CStringChecker smaller is an accomplishment on its own :)

lib/StaticAnalyzer/Checkers/CStringChecker.cpp

if (stateZeroSize && !stateNonZeroSize) {
     C.addTransition(stateZeroSize);
     return;
   }
 
   // If the size can be nonzero, we have to check the other arguments.
   if (stateNonZeroSize) {
     state = stateNonZeroSize;
 
-    // Ensure the destination is not null. If it is NULL there will be a
-    // NULL pointer dereference.
-    state = checkNonNull(C, state, Dest, destVal);
-    if (!state)
-      return;
-
-    // Get the value of the Src.
-    SVal srcVal = state->getSVal(Source, LCtx);
-
-    // Ensure the source is not null. If it is NULL there will be a
-    // NULL pointer dereference.
-    state = checkNonNull(C, state, Source, srcVal);
-    if (!state)
-      return;
-
     // Ensure the accesses are valid and that the buffers do not overlap.
     const char * const writeWarning =
       "Memory copy function overflows destination buffer";
     state = CheckBufferAccess(C, state, Size, Dest, Source,
                               writeWarning, /* sourceWarning = */ nullptr);
     if (Restricted)
       state = CheckOverlap(C, state, Size, Dest, Source);
 
void CStringChecker::evalMemset(CheckerContext &C, const CallExpr *CE) const {
   // If the size is zero, there won't be any actual memory access, so
   // just bind the return value to the Mem buffer and return.
   if (StateZeroSize && !StateNonZeroSize) {
     StateZeroSize = StateZeroSize->BindExpr(CE, LCtx, MemVal);
     C.addTransition(StateZeroSize);
     return;
   }
 
-  // Ensure the memory area is not null.
-  // If it is NULL there will be a NULL pointer dereference.
-  State = checkNonNull(C, StateNonZeroSize, Mem, MemVal);
-  if (!State)
-    return;
-
   State = CheckBufferAccess(C, State, Size, Mem);
   if (!State)
     return;
   State = InvalidateBuffer(C, State, Mem, C.getSVal(Mem),
                            /*IsSourceBuffer*/false, Size);
   if (!State)
     return;