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Re: Comparison of GCC-4.9 and LLVM-3.4 performance on SPECInt2000 for x86-64 and ARM
- From: Marc Glisse <marc dot glisse at inria dot fr>
- To: Vladimir Makarov <vmakarov at redhat dot com>
- Cc: Richard Biener <richard dot guenther at gmail dot com>, Renato Golin <renato dot golin at linaro dot org>, Bingfeng Mei <bmei at broadcom dot com>, Ramana Radhakrishnan <ramana dot radhakrishnan at arm dot com>, "gcc.gcc.gnu.org" <gcc at gcc dot gnu dot org>
- Date: Wed, 25 Jun 2014 16:37:21 +0200 (CEST)
- Subject: Re: Comparison of GCC-4.9 and LLVM-3.4 performance on SPECInt2000 for x86-64 and ARM
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On Wed, 25 Jun 2014, Vladimir Makarov wrote:
Maybe. But in this case LLVM did a right thing. The variable addressing was
through a restrict pointer.
Ah, gcc implements (on purpose?) a weak version of restrict, where it only
considers that 2 restrict pointers don't alias, whereas all other
compilers assume that restrict pointers don't alias other non-derived
pointers (see several PRs in bugzilla). I believe Richard recently added
code that would make implementing the strong version of restrict easier.
Maybe that's what is missing here?