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Re: libgo patch committed: Compile math library with -ffp-contract=off
- From: Ian Lance Taylor <iant at google dot com>
- To: Michael Hudson-Doyle <michael dot hudson at linaro dot org>
- Cc: gcc-patches <gcc-patches at gcc dot gnu dot org>, "gofrontend-dev at googlegroups dot com" <gofrontend-dev at googlegroups dot com>
- Date: Thu, 13 Mar 2014 18:43:34 -0700
- Subject: Re: libgo patch committed: Compile math library with -ffp-contract=off
- Authentication-results: sourceware.org; auth=none
- References: <mcrob1cc9pc dot fsf at iant-glaptop dot roam dot corp dot google dot com> <87mwgt602z dot fsf at canonical dot com>
On Thu, Mar 13, 2014 at 6:27 PM, Michael Hudson-Doyle
<michael.hudson@linaro.org> wrote:
> Ian Lance Taylor <iant@google.com> writes:
>
>> The bug report http://golang.org/issue/7074 shows that math.Log2(1)
>> produces the wrong result on Aarch64, because the Go math package is
>> compiled to use a fused multiply-add instruction. This patch to the
>> libgo configure script will use -ffp-contract=off when compiling the
>> math package on processors other than x86. Bootstrapped and ran Go
>> testsuite on x86_64-unknown-linux-gnu, not that that tests much.
>> Committed to mainline.
>
> Thanks for this! If you are willing to go into battle enough to argue
> that libgcc should also be compiled with -ffp-contract=off (I did not
> have the stomach for that fight) then we'll be down to 1 check-go
> failure on aarch64 (which is peano -- due to the absence of
> split/copyable stacks and should probably xfail).
Hmmm, what is it that fails with libgcc? Is there a bug report for
it?
I agree that peano is likely to fail without split stacks.
Ian