From: Maxim Kuvyrkov <maxim@codesourcery.com>
To: naga raj <gnuuser.raj@gmail.com>
Cc: gcc-help <gcc-help@gcc.gnu.org>
Subject: Re: loop-unrolling in gcc-4.6.2
Date: Mon, 26 Nov 2012 06:43:00 -0000 [thread overview]
Message-ID: <06230AFE-EC8F-4F19-BFCF-E7D1D6DF6CBE@codesourcery.com> (raw)
In-Reply-To: <CAKuVEhDXXA24veEaWNhek4v1N2ZYsw31dQ1KP8+BLcMudhZCEA@mail.gmail.com>
On 24/11/2012, at 4:02 AM, naga raj wrote:
> Hi,
>
> I am using Gcc-4.6.2 compiler ported to an embedded target.
> I am running a CoreMark benchmark code using -funroll-loops option
> Surprisingly I found that loops are not unrolled.
> But the same code when compiled with older toolchain version(with
> Gcc-4.1.2) is generating loop unrolling correctly.
>
> Should we need to add anything related to Unrolling to the target. I
> did not find the right document about this.
>
> Can any one please point me to the right direction...
There are several options that control loop unrolling in GCC, you could try tweaking them. See GCC manual at http://gcc.gnu.org/onlinedocs/gcc-4.6.3/gcc/Optimize-Options.html . Now, given that this is a well-known benchmark you are looking at, there is a real possibility that GCC port for your target accidentally prevents loop-unrolling optimization. You need to investigate why the instruction sequence your port is producing does not allow loop-unroller to do its job.
-funroll-loops
Unroll loops whose number of iterations can be determined at compile time or upon entry to the loop. -funroll-loops implies -frerun-cse-after-loop. This option makes code larger, and may or may not make it run faster.
-funroll-all-loops
Unroll all loops, even if their number of iterations is uncertain when the loop is entered. This usually makes programs run more slowly. -funroll-all-loops implies the same options as -funroll-loops,
And --param options:
max-unrolled-insns
The maximum number of instructions that a loop should have if that loop is unrolled, and if the loop is unrolled, it determines how many times the loop code is unrolled.
max-average-unrolled-insns
The maximum number of instructions biased by probabilities of their execution that a loop should have if that loop is unrolled, and if the loop is unrolled, it determines how many times the loop code is unrolled.
max-unroll-times
The maximum number of unrollings of a single loop.
--
Maxim Kuvyrkov
CodeSourcery/Mentor Graphics
next prev parent reply other threads:[~2012-11-26 6:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-23 15:02 naga raj
2012-11-26 6:43 ` Maxim Kuvyrkov [this message]
2012-11-26 8:31 ` naga raj
2012-11-30 2:13 ` Maxim Kuvyrkov
2012-11-30 4:02 ` naga raj
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