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Re: [RFC] [autovect patch] Implement vectorization hints
- From: Zack Weinberg <zack at codesourcery dot com>
- To: Devang Patel <dpatel at apple dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Sat, 26 Feb 2005 21:50:32 -0800
- Subject: Re: [RFC] [autovect patch] Implement vectorization hints
- References: <B397FD6A-85F5-42B2-8F66-E2BF57641F31@apple.com>
Devang Patel <email@example.com> writes:
> This patch implements two #pragmas that developers can use to give
> hints to auto vectorization pass. These pragmas are inserted in the
> source file before the loop. They are effective only on the very next
> loop in the source file.
> "#pragma novector" instructs compiler to not vectorize the
> loop. Programmer may decide to do so for various reasons.
> "#pragma ivdep" instructs compiler to ignore possible data dependence
> when data dependence analyzer is not able determine it. This is useful
> in a situation where compiler does not have enough information to
> prove data independence, but developer knows about it.
I have not read your code in any detail, and do not intend to, but
please permit me to point out that GCC-specific #pragmas should begin
"#pragma GCC" (you do this with the namespace argument to
c_register_pragma - note the line immediately above the two you
added). If these #pragmas are compatible with some other compiler,
please document which compiler that is.
Also, if I was just going along reading code and I saw
#pragma [GCC] ivdep, I would have no idea what it did. Could you
please use a more descriptive name, e.g.
#pragma GCC ignore_data_dependencies? (Ignore this critique if it's
"ivdep" for compatibility with some other compiler.)
Finally, I notice that your test cases are inconsistent with your code.