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From: "juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/113087] [14] RISC-V rv64gcv vector: Runtime mismatch
 with rv64gc
Date: Wed, 10 Jan 2024 23:09:42 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113087

--- Comment #31 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
(In reply to Patrick O'Neill from comment #30)
> (In reply to Li Pan from comment #29)
> > Thanks a lot for the summary. Could you please help to share some more
> > information about the spec2017 for above data? Like data set (test, tra=
in,
> > or ref), the enviornment (qemu, spike, or hardware) as well as the spec
> > config file. Just would like to make sure we are on the same page for t=
he
> > failures and reproducible from others.
>=20
> Hi Pan,
>=20
> We use nix to build/run spec so it's a bit opaque to me but I've extracted
> out:
> ref data set
> qemu
> flags:
> "-Ofast"
> "-mtune=3Dgeneric-ooo"
> "-march=3Drv64imafdcv_zba_zbb_zbs_zicond_zfa"
> "-fno-lto"
> "-ftree-vectorize"
> "--param=3Driscv-autovec-preference=3Dscalable"
>=20
> There are other flags that are are injected by the nix harness and I'm in
> the process of pulling them out. With these flags you should at least see
> the cam4 failure. Vineet is looking at the cam4 failure and is planning to
> open a bugzilla with details.
>=20
> Thanks,
> Patrick

You are using -Ofast which will have precision issue on floating-point.

You can reference it:

https://godbolt.org/z/zzG8xbx95

O3 result: 50002896.000000
Ofast result: 50005000.000000

They are different and not correctness issue.

GCC is same behavior as LLVM.

More details:
https://github.com/llvm/llvm-project/issues/77044

So, to elide the potential floating-point precision confusion,
I suggest you first use -O3 -ftrapping-math to test SPEC.

Otherwise, it's really hard to locate the real issue.=