Re: [PATCH PR84969]Don't reorder builtin memsets if they set different rhs values

[Martin Liška <mliska at suse dot cz>]

On 03/20/2018 07:18 PM, Bin Cheng wrote:
> Hi,
> As noted in PR84969, fuse_memset_builtins breaks dependence between different memsets.
> Specifically, it reorders different builtin memset partitions though it doesn't merge
> them in the end.  This simple patch fixes this wrong code issue by checking if any two
> builtin memsets set the same rhs value or not.  Note we don't need to bother if two
> memsets intersect with each other or not.
>
> Of course, this would miss opportunity merging S1/S3 in below case:
>    memset(p+12, 0, 12);   //<-----S1
>    memset(p+17, 1, 10);
>    memset(p, 0, 12);      //<-----S3
> In my opinion, this should be resolved in a more general way maximizing parallelism
> as well as merging opportunities when sorting partitions into topological order from
> dependence graph, which isn't GCC8 task.
>
> Bootstrap and test on x86_64 and AArch64 ongoing.  Okay if no failures?
>
> Thanks,
> bin
>
> 2018-03-20  Bin Cheng  <bin.cheng@arm.com>
>
> 	PR tree-optimization/84969
> 	* tree-loop-distribution.c (fuse_memset_builtins): Don't reorder
> 	builtin memset partitions if they set differnt rhs values.
>
> gcc/testsuite
> 2018-03-20  Bin Cheng  <bin.cheng@arm.com>
>
> 	PR tree-optimization/84969
> 	* gcc.dg/tree-ssa/pr84969.c: New test.

Thanks Bin.

I can confirm it fixes regression tests of postgres w/ -O3.

Martin