[Beignet] [PATCH 1/5] GBE: refine Phi copy interfering check.

[Zhigang Gong]

Ping for review.
Thanks.

On Tue, Sep 01, 2015 at 12:04:59PM +0800, Zhigang Gong wrote:
> If the PHI source register's definition instruction uses the
> phi register, it is not a interfere. For an example:
> 
> MOV %phi, %phicopy
> ...
> ADD %phiSrcDef, %phi, tmp
> ...
> MOV %phicopy, %phiSrcDef
> ...
> 
> The %phi and the %phiSrcDef is not interering each other.
> Simply advancing the start of the check to next instruction is
> enough to get better result. For some special case, this patch
> could get significant performance boost.
> 
> Signed-off-by: Zhigang Gong <zhigang.gong at intel.com>
> ---
>  backend/src/llvm/llvm_gen_backend.cpp | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/backend/src/llvm/llvm_gen_backend.cpp b/backend/src/llvm/llvm_gen_backend.cpp
> index 4905415..38c63ce 100644
> --- a/backend/src/llvm/llvm_gen_backend.cpp
> +++ b/backend/src/llvm/llvm_gen_backend.cpp
> @@ -2220,6 +2220,8 @@ namespace gbe
>  
>              ir::BasicBlock::const_iterator iter = ir::BasicBlock::const_iterator(phiCopySrcDefInsn);
>              ir::BasicBlock::const_iterator iterE = bb->end();
> +
> +            iter++;
>              // check no use of phi in this basicblock between [phiCopySrc def, bb end]
>              bool phiPhiCopySrcInterfere = false;
>              while (iter != iterE) {
> -- 
> 1.9.1
> 
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