In C++ and C2x, we would avoid calling ImplicitlyDefineFunction at all,
but in OpenCL mode we would still call the function and have it produce
an error diagnostic. Instead, we now have a helper function to
determine when implicit function definitions are allowed and we use
that to determine whether to call ImplicitlyDefineFunction so that the
behavior is more consistent across language modes.
This changes the diagnostic behavior from telling the users that an
implicit function declaration is not allowed in OpenCL to reporting use
of an unknown identifier and going through typo correction, as done in
C++ and C2x.
C89 had a questionable feature where the compiler would implicitly
declare a function that the user called but was never previously
declared. The resulting function would be globally declared as
extern int func(); -- a function without a prototype which accepts zero
or more arguments.
C99 removed support for this questionable feature due to severe
security concerns. However, there was no deprecation period; C89 had
the feature, C99 didn't. So Clang (and GCC) both supported the
functionality as an extension in C99 and later modes.
C2x no longer supports that function signature as it now requires all
functions to have a prototype, and given the known security issues with
the feature, continuing to support it as an extension is not tenable.
This patch changes the diagnostic behavior for the
-Wimplicit-function-declaration warning group depending on the language
mode in effect. We continue to warn by default in C89 mode (due to the
feature being dangerous to use). However, because this feature will not
be supported in C2x mode, we've diagnosed it as being invalid for so
long, the security concerns with the feature, and the trivial
workaround for users (declare the function), we now default the
extension warning to an error in C99-C17 mode. This still gives users
an easy workaround if they are extensively using the extension in those
modes (they can disable the warning or use -Wno-error to downgrade the
error), but the new diagnostic makes it more clear that this feature is
not supported and should be avoided. In C2x mode, we no longer allow an
implicit function to be defined and treat the situation the same as any
other lookup failure.
Differential Revision: https://reviews.llvm.org/D122983
This removed the pointless need for extension pragma since
it doesn't disable anything properly and it doesn't need to
enable anything that is not possible to disable.
The change doesn't break existing kernels since it allows to
compile more cases i.e. without pragma statements but the
pragma continues to be accepted.
Differential Revision: https://reviews.llvm.org/D100985
Aaron Ballman