[cfe-dev] What's the rationale to continue declare compatibility with GCC 4.2.1?

JF Bastien via cfe-dev cfe-dev at lists.llvm.org
Fri Jul 19 04:50:38 PDT 2019

> On Jul 17, 2019, at 2:13 PM, James Y Knight via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> The reason has always been that changing it would undoubtedly break some software which uses features of newer GCCs that aren't implemented in Clang. And there are indeed some of those features, even if they are weird edge cases.

What you’re saying leads me to believe that https://reviews.llvm.org/rL365962 <https://reviews.llvm.org/rL365962> shouldn’t have been committed. Unless we now decide it’s OK to break code which check GCC quirks?

> Also, by this point, Clang is a widely-enough used compiler, that I'd expect most maintained software to be attempting to support it explicitly -- best via __has_builtin/__has_feature/__has_attribute/etc tests as applicable, falling back to the GCC version check if those macros don't exist.
> On Wed, Jul 17, 2019 at 7:22 AM Simon Atanasyan via cfe-dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
> Hi,
> Recently I get a request to implement in Clang a MIPS-related feature
> which exists in GCC pre 4.4 and removed in later versions. There is a
> rationale behind such strange request -- third-party software checks a
> compiler's compatibility using __GNUC__,__GNUC_MINOR__ macros and
> selects code dedicated for obsoleted version of GCC.
> As to me I would use for __GNUC__,__GNUC_MINOR__,__GNUC_PATCHLEVEL__
> macros defined in the InitializePredefinedMacros function the same
> values as a minimal GCC version required for building LLVM/Clang [1].
> Now it's 5.1.0.
> Is there any rationale to continue declare compatibility with old GCC 4.2.1?
> [1] https://llvm.org/docs/GettingStarted.html#software <https://llvm.org/docs/GettingStarted.html#software>
> -- 
> Simon Atanasyan
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