XL considers different vector types to be incompatible with each other.
For example assignment between variables of types vector float and vector
long long or even vector signed int and vector unsigned int are diagnosed.
clang, however does not diagnose such cases and does a simple bitcast between
the two types. This could easily result in program errors. This patch is to
fix the implicit casts in altivec.h so that there is no incompatible vector
type errors whit -fno-lax-vector-conversions, this is the prerequisite patch
to switch the default to -fno-lax-vector-conversions later.
Reviewed By: nemanjai, amyk
Differential Revision: https://reviews.llvm.org/D124093
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
Maryam Moghadas