[clang] [Clang][Sema] Add -Wstringop-overread warning for source buffer overreads (PR #183004)

[Erich Keane via cfe-commits]

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@@ -1414,16 +1479,47 @@ void Sema::checkFortifiedBuiltinMemoryFunction(FunctionDecl *FD,
   case Builtin::BImempcpy:
   case Builtin::BI__builtin_mempcpy: {
     DiagID = diag::warn_fortify_source_overflow;
-    SourceSize = ComputeExplicitObjectSizeArgument(TheCall->getNumArgs() - 1);
-    DestinationSize = ComputeSizeArgument(0);
+    SourceSize =
+        Checker.ComputeExplicitObjectSizeArgument(TheCall->getNumArgs() - 1);
+    DestinationSize = Checker.ComputeSizeArgument(0);
+
+    // Buffer overread doesn't make sense for memset.
+    if (BuiltinID != Builtin::BImemset &&
+        BuiltinID != Builtin::BI__builtin_memset) {
+      checkSourceBufferOverread(FD, TheCall, /*SrcArgIdx=*/1, /*SizeArgIdx=*/2,
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erichkeane wrote:

Same here.

https://github.com/llvm/llvm-project/pull/183004