Re: [PATCH] Handle "omp simd array" accesses in ifcvt_memrefs_wont_trap

[Richard Biener <rguenther@suse.de>]

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On Fri, 31 May 2019, Jakub Jelinek wrote:

> Hi!
> 
> As a preparation for lastprivate(conditional:) on #pragma omp simd, I need
> if-conversion to handle "omp simd array" accesses.  These are safe, no
> matter whether written or read, each simd lane accesses their own element,
> after the vectorization it is all just a single vector read or store or RMW
> cycle, it will never trap (it is an automatic variable), it will never be
> out of bounds (the index is guaranteed to be within the bounds of the array,
> as the array is sized to the vectorization factor and index is the simd lane
> number within that vectorization factor).
> 
> Tested on x86_64-linux with vect.exp, ok for trunk if it passes full
> bootstrap/regtest?

Hmm.  Is it enough to set TREE_THIS_NOTRAP on the ARRAY_REF instead?
At least it's documented the ARRAY_REF then isn't the issue.
As for conditional vs. unconditional I'm not so sure but automatic
vars are excepmted from that anyways?

Richard.

> 2019-05-31  Jakub Jelinek  <jakub@redhat.com>
> 
> 	* tree-if-conv.c: Include attribs.h.
> 	(ifcvt_memrefs_wont_trap): Return true for ARRAY_REF access to
> 	"omp simd array" variable with .GOMP_SIMD_LANE as index.
> 
> 	* gcc.dg/vect/vect-cond-12.c: New test.
> 
> --- gcc/tree-if-conv.c.jj	2019-05-14 21:37:32.932400472 +0200
> +++ gcc/tree-if-conv.c	2019-05-31 11:13:13.558732900 +0200
> @@ -120,6 +120,7 @@ along with GCC; see the file COPYING3.
>  #include "fold-const.h"
>  #include "tree-ssa-sccvn.h"
>  #include "tree-cfgcleanup.h"
> +#include "attribs.h"
>  
>  /* Only handle PHIs with no more arguments unless we are asked to by
>     simd pragma.  */
> @@ -897,6 +898,32 @@ ifcvt_memrefs_wont_trap (gimple *stmt, v
>    if (DR_W_UNCONDITIONALLY (*master_dr))
>      return true;
>  
> +  /* OpenMP simd lane accesses to omp simd array variables are always
> +     within bounds and can be handled as if it was unconditional.  */
> +  tree base_var = get_base_address (base);
> +  if (VAR_P (base_var)
> +      && lookup_attribute ("omp simd array", DECL_ATTRIBUTES (base_var)))
> +    {
> +      tree ref = DR_REF (a);
> +      struct loop *loop = loop_containing_stmt (stmt);
> +      if (loop->simduid
> +	  && TREE_CODE (ref) == ARRAY_REF
> +	  && TREE_CODE (TREE_OPERAND (ref, 1)) == SSA_NAME)
> +	{
> +	  gimple *def = SSA_NAME_DEF_STMT (TREE_OPERAND (ref, 1));
> +	  if (is_gimple_call (def)
> +	      && gimple_call_internal_p (def)
> +	      && (gimple_call_internal_fn (def) == IFN_GOMP_SIMD_LANE))
> +	    {
> +	      tree arg = gimple_call_arg (def, 0);
> +	      gcc_assert (TREE_CODE (arg) == SSA_NAME);
> +	      arg = SSA_NAME_VAR (arg);
> +	      if (arg == loop->simduid)
> +		return true;
> +	    }
> +	}
> +    }
> +
>    /* If a is unconditionally accessed then ...
>  
>       Even a is conditional access, we can treat it as an unconditional
> --- gcc/testsuite/gcc.dg/vect/vect-cond-12.c.jj	2019-05-31 11:25:33.203577504 +0200
> +++ gcc/testsuite/gcc.dg/vect/vect-cond-12.c	2019-05-31 11:26:58.616174115 +0200
> @@ -0,0 +1,14 @@
> +/* { dg-do compile } */
> +/* { dg-additional-options "-fopenmp-simd" } */
> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" { target vect_condition } } } */
> +
> +int x;
> +
> +void
> +foo (int *a)
> +{
> +  #pragma omp simd lastprivate (x)
> +  for (int i = 0; i < 1024; ++i)
> +    if (a[i])
> +      x = i;
> +}
> 
> 	Jakub
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany;
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