Sema::checkPointerTypesForAssignment calls IsFunctionConversion with From/To reversed

[dougsonos]

At the end of Sema::checkPointerTypesForAssignment:

  if (!S.getLangOpts().CPlusPlus &&
      S.IsFunctionConversion(ltrans, rtrans, ltrans))

ltrans and rtrans are the left and right sides of the assignment, and are therefore the destination and source types, respectively.

But:

bool Sema::IsFunctionConversion(QualType FromType, QualType ToType,
                                QualType &ResultTy) {

Here the source is first and the destination is second.

Maybe this a bug that has gone unnoticed because IsFunctionConversion tends to work symmetrically? (speculating)

Or maybe there is a good reason for checkPointerTypesForAssignment to invert the parameters, but it's not commented or at all apparent by source inspection.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Doug Wyatt (dougsonos)

At the end of `Sema::checkPointerTypesForAssignment`: ``` if (!S.getLangOpts().CPlusPlus && S.IsFunctionConversion(ltrans, rtrans, ltrans)) ```

ltrans and rtrans are the left and right sides of the assignment, and are therefore the destination and source types, respectively.

But:

bool Sema::IsFunctionConversion(QualType FromType, QualType ToType,
                                QualType &ResultTy) {

Here the source is first and the destination is second.

Maybe this a bug that has gone unnoticed because IsFunctionConversion tends to work symmetrically? (speculating)

Or maybe there is a good reason for checkPointerTypesForAssignment to invert the parameters, but it's not commented or at all apparent by source inspection.

[Sirraide]

It’s also worth noting that, right below that, we also inconsistently pass the LHS and RHS as the FromType and ToType of other functions (comments added):

  if (IsInvalidCmseNSCallConversion(S, /*FromType=*/ltrans, /*ToType=*/rtrans))
  if (S.IsInvalidSMECallConversion(    /*FromType=*/rtrans, /*ToType=*/ltrans))

[shafik]

So those lines look like there were touched by:

@sdesmalen-arm via 28b5f30
@momchil-velikov via 080d046
@zygoloid via 3c4f8d2