On Mon, 18 Jan 2021, Arnd Bergmann <a...@kernel.org> wrote:
On Mon, Jan 18, 2021 at 11:56 AM Adrian Ratiu
<adrian.ra...@collabora.com> wrote:
From: Nathan Chancellor <natechancel...@gmail.com>
Drop warning because kernel now requires GCC >= v4.9 after
commit 6ec4476ac825 ("Raise gcc version requirement to 4.9")
and clarify that -ftree-vectorize now always needs enabling for
GCC by directly testing the presence of CONFIG_CC_IS_GCC.
Another reason to remove the warning is that Clang exposes
itself as GCC < 4.6 so it triggers the warning about GCC which
doesn't make much sense and risks misleading users.
As a side-note remark, -fttree-vectorize is on by default in
Clang, but it currently does not work (see linked issues).
Link: https://github.com/ClangBuiltLinux/linux/issues/496 Link:
https://github.com/ClangBuiltLinux/linux/issues/503
Reported-by: Nick Desaulniers <ndesaulni...@google.com>
Reviewed-by: Nick Desaulniers <ndesaulni...@google.com>
Signed-off-by: Nathan Chancellor <natechancel...@gmail.com>
Signed-off-by: Adrian Ratiu <adrian.ra...@collabora.com>
Shouldn't there be a check for whatever minimum version of clang
produces optimized code now? As I understand it, the warning was
originally meant to complain about both old gcc and any version
of clang, while waiting for a new version of clang to produce
vectorized code.
Has that happened now?
No, clang does not produce vectorized code by default, not even
with the -ftree-vectorize flag explicitely added like in the next
patch in this series (that flag is enabled by default in clang
anyway, so no effect).
Clang needs more investigation and testing because with additional
code changes it can be "forced" to output vectorized code, but
that is outside the scope of this series.
If you think it's a good idea I can add a warning only for Clang
which makes more sense than telling clang users to upgrade their
GCC, since now Clang is officially supported. What do you think?
Arnd
