C++03 mode ignores the arg in [[attribute(arg)]]

[AMP999]

https://godbolt.org/z/aPKq1sKPT
[[gnu::assume_aligned(4)]] static void *g() { return p; }
In -std=c++11 mode, this code is accepted and works as expected. In -std=c++03 mode, it seems to ignore the (4) argument for some reason, and I get an error:

<source>:5:3: error: 'assume_aligned' attribute takes at least 1 argument
    5 | [[gnu::assume_aligned(4)]] static void *g() { return p; }
      |   ^

@philnik777 I think you enabled attributes in 874217f; is there something missing to enable attributes with arguments?

The problem is these lines in ParseCXX11AttributeArgs.

  // If the attribute isn't known, we will not attempt to parse any
  // arguments.
  if (Form.getSyntax() != ParsedAttr::AS_Microsoft &&
      !hasAttribute(LO.CPlusPlus ? AttributeCommonInfo::Syntax::AS_CXX11
                                 : AttributeCommonInfo::Syntax::AS_C23,
                    ScopeName, AttrName, getTargetInfo(), getLangOpts())) {

This is reusing the return code of hasAttribute to ask whether the attribute is recognized (a boolean). But the machine-generated code in AttrHasAttributeImpl.inc uses the return code to say what __has_cpp_attribute should be set to (an int), and invariably returns 0 in C++03 mode. https://godbolt.org/z/casKPfdez

} else if (ScopeName == "gnu") {
  return llvm::StringSwitch<int>(Name)
[...]
    .Case("assume_aligned", LangOpts.CPlusPlus11 ? 1 : 0)

That file is generated by clang/utils/TableGen/ClangAttrEmitter.cpp. Maybe a change is needed in that generator?

[philnik777]

I noticed that __has_cpp_attribute is broken a couple weeks ago myself, but I didn't realize that this breaks attribute parsing. I haven't had time to look at it closely yet, but the generator looks like a pretty good start. Do you want to work on that? If not, I'll try to fix this in the next few days, since it's more severe than I thought.

[philnik777]

@AaronBallman do you think it's worth back-porting a fix for this?

[AaronBallman]

If the fix is small and obviously correct, then yes, I think that's worth backporting.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Amirreza Ashouri (AMP999)

https://godbolt.org/z/aPKq1sKPT `[[gnu::assume_aligned(4)]] static void *g() { return p; }` In `-std=c++11` mode, this code is accepted and works as expected. In `-std=c++03` mode, it seems to ignore the `(4)` argument for some reason, and I get an error: ``` <source>:5:3: error: 'assume_aligned' attribute takes at least 1 argument 5 | [[gnu::assume_aligned(4)]] static void *g() { return p; } | ^ ``` @philnik777 I think you enabled attributes in 874217f; is there something missing to enable attributes with arguments?

The problem is these lines in ParseCXX11AttributeArgs.

  // If the attribute isn't known, we will not attempt to parse any
  // arguments.
  if (Form.getSyntax() != ParsedAttr::AS_Microsoft &&
      !hasAttribute(LO.CPlusPlus ? AttributeCommonInfo::Syntax::AS_CXX11
                                 : AttributeCommonInfo::Syntax::AS_C23,
                    ScopeName, AttrName, getTargetInfo(), getLangOpts())) {

This is reusing the return code of hasAttribute to ask whether the attribute is recognized (a boolean). But the machine-generated code in AttrHasAttributeImpl.inc uses the return code to say what __has_cpp_attribute should be set to (an int), and invariably returns 0 in C++03 mode. https://godbolt.org/z/casKPfdez

} else if (ScopeName == "gnu") {
  return llvm::StringSwitch<int>(Name)
[...]
    .Case("assume_aligned", LangOpts.CPlusPlus11 ? 1 : 0)

That file is generated by clang/utils/TableGen/ClangAttrEmitter.cpp. Maybe a change is needed in that generator?

[llvmbot]

@llvm/issue-subscribers-c-1

Author: Amirreza Ashouri (AMP999)

https://godbolt.org/z/aPKq1sKPT `[[gnu::assume_aligned(4)]] static void *g() { return p; }` In `-std=c++11` mode, this code is accepted and works as expected. In `-std=c++03` mode, it seems to ignore the `(4)` argument for some reason, and I get an error: ``` <source>:5:3: error: 'assume_aligned' attribute takes at least 1 argument 5 | [[gnu::assume_aligned(4)]] static void *g() { return p; } | ^ ``` @philnik777 I think you enabled attributes in 874217f; is there something missing to enable attributes with arguments?

The problem is these lines in ParseCXX11AttributeArgs.

  // If the attribute isn't known, we will not attempt to parse any
  // arguments.
  if (Form.getSyntax() != ParsedAttr::AS_Microsoft &&
      !hasAttribute(LO.CPlusPlus ? AttributeCommonInfo::Syntax::AS_CXX11
                                 : AttributeCommonInfo::Syntax::AS_C23,
                    ScopeName, AttrName, getTargetInfo(), getLangOpts())) {

This is reusing the return code of hasAttribute to ask whether the attribute is recognized (a boolean). But the machine-generated code in AttrHasAttributeImpl.inc uses the return code to say what __has_cpp_attribute should be set to (an int), and invariably returns 0 in C++03 mode. https://godbolt.org/z/casKPfdez

} else if (ScopeName == "gnu") {
  return llvm::StringSwitch<int>(Name)
[...]
    .Case("assume_aligned", LangOpts.CPlusPlus11 ? 1 : 0)

That file is generated by clang/utils/TableGen/ClangAttrEmitter.cpp. Maybe a change is needed in that generator?