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Re: Comparison of GCC-4.9 and LLVM-3.4 performance on SPECInt2000 for x86-64 and ARM

From: Ramana Radhakrishnan <ramana dot radhakrishnan at arm dot com>
To: Renato Golin <renato dot golin at linaro dot org>, Vladimir Makarov <vmakarov at redhat dot com>
Cc: "gcc.gcc.gnu.org" <gcc at gcc dot gnu dot org>
Date: Tue, 24 Jun 2014 15:58:09 +0100
Subject: Re: Comparison of GCC-4.9 and LLVM-3.4 performance on SPECInt2000 for x86-64 and ARM
Authentication-results: sourceware.org; auth=none
References: <53A98705 dot 10909 at redhat dot com> <CAMSE1kf_cjTDnT3+2Tts71_bX_DCyGgk2p=UTBAzF8kUp4ybVQ at mail dot gmail dot com>

I wonder how much of that is due to auto-vectorization (on LLVM, -O2+
turns it on, I suppose GCC is only on -O3?). From Ramana's point,
there may be nothing serious if you haven't enabled NEON, though.


Auto-vec is turned off when you have -mfpu=vfpv3-d16 . That implies No Neon.

Ramana


Also interesting to see the impact of LTO being a major drive in
recent performance improvements on both compilers.

cheers,
--renato

References:
- Comparison of GCC-4.9 and LLVM-3.4 performance on SPECInt2000 for x86-64 and ARM
  - From: Vladimir Makarov
- Re: Comparison of GCC-4.9 and LLVM-3.4 performance on SPECInt2000 for x86-64 and ARM
  - From: Renato Golin

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