[Beignet] [PATCH] GBE: disable MulAdd pattern in instruction selection temporarily.

[Song, Ruiling]

After my investigation, I find the unite test depends on mad optimization which is not quite reasonable.
So, I change the unit test to directly call mad(). And also directly map mad() builtin to ISA mad.
I have sent the patches, welcome any comments. Thanks!

Ruiling
-----Original Message-----
From: Song, Ruiling 
Sent: Monday, November 04, 2013 4:24 PM
To: Zhigang Gong
Cc: beignet at lists.freedesktop.org
Subject: RE: [Beignet] [PATCH] GBE: disable MulAdd pattern in instruction selection temporarily.

In fact, even if user set 'FP_CONTRACT ON', we can also choose not do 'mad optimization.'
It depends on us whether or not do the contraction. "Contract on" is just a hint.
Obviously contract on will get better speed and accuracy.

I think the compiler_menger_sponge_no_shadow fail because of accuracy. Its reference is got with mad instruction.
I think we can use the new result to replace the reference, there should be not too much difference. If they differ too much, then it would be a bug.


-----Original Message-----
From: Zhigang Gong [mailto:zhigang.gong at linux.intel.com]
Sent: Monday, November 04, 2013 3:41 PM
To: Song, Ruiling
Cc: beignet at lists.freedesktop.org
Subject: Re: [Beignet] [PATCH] GBE: disable MulAdd pattern in instruction selection temporarily.

This patch breaks utests compiler_menger_sponge_no_shadow.
Actually, my first feeling of this patch is that it assumes that FP_CONTRACT is always off and may be cause problem if this assumption is incorrect. The unit test case compiler_menger_sponge_no_shadow should be one of that case.

Any thoughts?

On Fri, Nov 01, 2013 at 02:16:08PM +0800, Ruiling Song wrote:
> The story starts from 'FP_CONTRACT'. In c99 spec, it describes 
> constract expression as:
> "A floating expression may be contracted, that is, evaluated as though 
> it were an atomic operation, thereby omitting rounding errors implied 
> by the source code and the expression evaluation method."
> 
> But user can use 'pragma FP_CONTRACT OFF' to disable float 
> contraction, in which condition, we should not do contraction like mad optimization.
> In SPIR 1.2, named metadata 'opencl.enable.FP_CONTRACT' will be used to do this.
> When Clang is ready, we need refine the backend logic.
> 
> Signed-off-by: Ruiling Song <ruiling.song at intel.com>
> ---
>  backend/src/backend/gen_insn_selection.cpp |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/backend/src/backend/gen_insn_selection.cpp
> b/backend/src/backend/gen_insn_selection.cpp
> index 7eae7ca..1f25f0e 100644
> --- a/backend/src/backend/gen_insn_selection.cpp
> +++ b/backend/src/backend/gen_insn_selection.cpp
> @@ -1856,6 +1856,9 @@ namespace gbe
>      {
>        using namespace ir;
>  
> +      // XXX TODO: we need a clean support of FP_CONTRACT to remove below line 'return false'
> +      // if 'pragma FP_CONTRACT OFF' is used in cl kernel, we should not do mad optimization.
> +      return false;
>        // MAD tend to increase liveness of the sources (since there are three of
>        // them). TODO refine this strategy. Well, we should be able at least to
>        // evaluate per basic block register pressure and selectively 
> enable
> --
> 1.7.9.5
> 
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