rsmith requested changes to this revision.
rsmith added a comment.
This revision now requires changes to proceed.
I'd like to see some testcases for the C++ side of this. The following things
all seem like they might be interesting: passing and returning classes and
unions, especially ones that aren't trivially-copyable, `nullptr_t`, pointers
to members, `this` parameters, VTTs, the "complete object" flag for MS ABI
constructors, the `this` return from constructors in the ARM ABI, parameters
and return values of virtual adjustment thunks.
================
Comment at: clang/lib/CodeGen/CGCall.cpp:1892
+ return true;
+ if (QTy->isScalarType()) {
+ if (const ComplexType *Complex = dyn_cast<ComplexType>(QTy))
----------------
This includes `nullptr_t` (which is never ` noundef`) and member pointers
(which are sometimes `noundef`, and you'll need to ask the `CXXABI`
implementation if you don't want to conservatively return `false`).
================
Comment at: clang/lib/CodeGen/CGCall.cpp:2110
+ DetermineNoUndef(RetTy, getTypes(), DL, RetAI)) {
+ RetAttrs.addAttribute(llvm::Attribute::NoUndef);
+ }
----------------
This only applies in C++. In C, it's valid for a function to omit its `return`
statement if the result value is unused, and in that case the returned value
will legitimately be `undef`.
Even in C++, we're conservative about enforcing the constraint that functions
return a proper value and control flow doesn't just fall off the bottom of the
function. See the full set of checks here:
https://github.com/llvm/llvm-project/blob/master/clang/lib/CodeGen/CodeGenFunction.cpp#L1322
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D81678/new/
https://reviews.llvm.org/D81678
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
