[analyzer] Fix crash in Stream checker when using void pointers (llvm#97199)

We can get zero type size (thus div by zero crash) if the region is for a 'void*' pointer.
In this patch, let's just override the void type with a char type to avoid the crash.

Fixes
llvm#93408 (comment)

Author: steakhal

clang/lib/StaticAnalyzer/Checkers/StreamChecker.cpp

@@ -1034,16 +1034,16 @@ void StreamChecker::preWrite(const FnDescription *Desc, const CallEvent &Call,
   C.addTransition(State);
 }
 
-static std::optional<QualType> getPointeeType(const MemRegion *R) {
+static QualType getPointeeType(const MemRegion *R) {
   if (!R)
-    return std::nullopt;
+    return {};
   if (const auto *ER = dyn_cast<ElementRegion>(R))
     return ER->getElementType();
   if (const auto *TR = dyn_cast<TypedValueRegion>(R))
     return TR->getValueType();
   if (const auto *SR = dyn_cast<SymbolicRegion>(R))
     return SR->getPointeeStaticType();
-  return std::nullopt;
+  return {};
 }
 
 static std::optional<NonLoc> getStartIndex(SValBuilder &SVB,
@@ -1073,7 +1073,8 @@ tryToInvalidateFReadBufferByElements(ProgramStateRef State, CheckerContext &C,
   const auto *Buffer =
       dyn_cast_or_null<SubRegion>(Call.getArgSVal(0).getAsRegion());
 
-  std::optional<QualType> ElemTy = getPointeeType(Buffer);
+  const ASTContext &Ctx = C.getASTContext();
+  QualType ElemTy = getPointeeType(Buffer);
   std::optional<SVal> StartElementIndex =
       getStartIndex(C.getSValBuilder(), Buffer);
 
@@ -1086,18 +1087,20 @@ tryToInvalidateFReadBufferByElements(ProgramStateRef State, CheckerContext &C,
   std::optional<int64_t> StartIndexVal =
       getKnownValue(State, StartElementIndex.value_or(UnknownVal()));
 
-  if (ElemTy && CountVal && Size && StartIndexVal) {
+  if (!ElemTy.isNull() && CountVal && Size && StartIndexVal) {
     int64_t NumBytesRead = Size.value() * CountVal.value();
-    int64_t ElemSizeInChars =
-        C.getASTContext().getTypeSizeInChars(*ElemTy).getQuantity();
+    int64_t ElemSizeInChars = Ctx.getTypeSizeInChars(ElemTy).getQuantity();
+    if (ElemSizeInChars == 0)
+      return nullptr;
+
     bool IncompleteLastElement = (NumBytesRead % ElemSizeInChars) != 0;
     int64_t NumCompleteOrIncompleteElementsRead =
         NumBytesRead / ElemSizeInChars + IncompleteLastElement;
 
     constexpr int MaxInvalidatedElementsLimit = 64;
     if (NumCompleteOrIncompleteElementsRead <= MaxInvalidatedElementsLimit) {
       return escapeByStartIndexAndCount(State, Call, C.blockCount(), Buffer,
-                                        *ElemTy, *StartIndexVal,
+                                        ElemTy, *StartIndexVal,
                                         NumCompleteOrIncompleteElementsRead);
     }
   }

clang/test/Analysis/stream.c

@@ -453,3 +453,48 @@ void getline_buffer_size_negative() {
   free(buffer);
   fclose(file);
 }
+
+void gh_93408_regression(void *buffer) {
+  FILE *f = fopen("/tmp/foo.txt", "r");
+  fread(buffer, 1, 1, f); // expected-warning {{Stream pointer might be NULL}} no-crash
+  fclose(f);
+}
+
+typedef void VOID;
+void gh_93408_regression_typedef(VOID *buffer) {
+  FILE *f = fopen("/tmp/foo.txt", "r");
+  fread(buffer, 1, 1, f); // expected-warning {{Stream pointer might be NULL}} no-crash
+  fclose(f);
+}
+
+struct FAM {
+  int data;
+  int tail[];
+};
+
+struct FAM0 {
+  int data;
+  int tail[0];
+};
+
+void gh_93408_regression_FAM(struct FAM *p) {
+  FILE *f = fopen("/tmp/foo.txt", "r");
+  fread(p->tail, 1, 1, f); // expected-warning {{Stream pointer might be NULL}}
+  fclose(f);
+}
+
+void gh_93408_regression_FAM0(struct FAM0 *p) {
+  FILE *f = fopen("/tmp/foo.txt", "r");
+  fread(p->tail, 1, 1, f); // expected-warning {{Stream pointer might be NULL}}
+  fclose(f);
+}
+
+struct ZeroSized {
+    int data[0];
+};
+
+void gh_93408_regression_ZeroSized(struct ZeroSized *buffer) {
+  FILE *f = fopen("/tmp/foo.txt", "r");
+  fread(buffer, 1, 1, f); // expected-warning {{Stream pointer might be NULL}} no-crash
+  fclose(f);
+}