[clang] [clang] Implement -Walloc-size diagnostic option (PR #150028)

[Vladimir Vuksanovic via cfe-commits]

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@@ -3542,6 +3542,56 @@ bool CallExpr::isBuiltinAssumeFalse(const ASTContext &Ctx) const {
          Arg->EvaluateAsBooleanCondition(ArgVal, Ctx) && !ArgVal;
 }
 
+const AllocSizeAttr *CallExpr::getCalleeAllocSizeAttr() const {
+  if (const FunctionDecl *DirectCallee = getDirectCallee())
+    return DirectCallee->getAttr<AllocSizeAttr>();
+  if (const Decl *IndirectCallee = getCalleeDecl())
+    return IndirectCallee->getAttr<AllocSizeAttr>();
+  return nullptr;
+}
+
+std::optional<llvm::APInt>
+CallExpr::getBytesReturnedByAllocSizeCall(const ASTContext &Ctx) const {
+  const AllocSizeAttr *AllocSize = getCalleeAllocSizeAttr();
+
+  assert(AllocSize && AllocSize->getElemSizeParam().isValid());
+  unsigned SizeArgNo = AllocSize->getElemSizeParam().getASTIndex();
+  unsigned BitsInSizeT = Ctx.getTypeSize(Ctx.getSizeType());
+  if (getNumArgs() <= SizeArgNo)
+    return {};
+
+  auto EvaluateAsSizeT = [&](const Expr *E, llvm::APSInt &Into) {
+    Expr::EvalResult ExprResult;
+    if (E->isValueDependent() ||
+        !E->EvaluateAsInt(ExprResult, Ctx, Expr::SE_AllowSideEffects))
+      return false;
+    Into = ExprResult.Val.getInt();
+    if (Into.isNegative() || !Into.isIntN(BitsInSizeT))
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vvuksanovic wrote:

I'm not sure I understand, isn't `size_t` guaranteed to be unsigned?

Also, this code isn't new, it was just moved here.

https://github.com/llvm/llvm-project/pull/150028