[PR,69355] Correct hole detection when total_scalarization fails

Hi,

PR 69355 has revealed that when SRA attempts total scalarization of an
aggregate but this fails because the user type-casts a scalar field
and stores into a it a smaller aggregate (and the scalar field is not
written to, whether directly or as a part of an aggregate store), the
pass can loose track of unscalarized data there.

I think that this can happen only when violating strict aliasing rules
but with -fno-strict-aliasing it should work.

Fixed thusly with the patch below (the condition is there to avoid
detecting padding after aggregate-fields in totally-scalarized
aggregates as unscalarized data).  Bootstrapped and tested on
x86_64-linux.  OK for trunk?  And the gcc-5 branch?

Thanks,

Martin


2016-01-26  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/69355
	* tree-sra.c (analyze_access_subtree): Correct hole detection when
	total_scalarization fails.

testsuite/
	* gcc.dg/tree-ssa/pr69355.c: New test.

---
 gcc/testsuite/gcc.dg/tree-ssa/pr69355.c | 44 +++++++++++++++++++++++++++++++++
 gcc/tree-sra.c                          |  2 +-
 2 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr69355.c

On Tue, 26 Jan 2016, Martin Jambor wrote:

> Hi,
> 
> PR 69355 has revealed that when SRA attempts total scalarization of an
> aggregate but this fails because the user type-casts a scalar field
> and stores into a it a smaller aggregate (and the scalar field is not
> written to, whether directly or as a part of an aggregate store), the
> pass can loose track of unscalarized data there.
> 
> I think that this can happen only when violating strict aliasing rules
> but with -fno-strict-aliasing it should work.
> 
> Fixed thusly with the patch below (the condition is there to avoid
> detecting padding after aggregate-fields in totally-scalarized
> aggregates as unscalarized data).  Bootstrapped and tested on
> x86_64-linux.  OK for trunk?  And the gcc-5 branch?

Ok.

Thanks,
Richard.

> Thanks,
> 
> Martin
> 
> 
> 2016-01-26  Martin Jambor  <mjambor@suse.cz>
> 
> 	PR tree-optimization/69355
> 	* tree-sra.c (analyze_access_subtree): Correct hole detection when
> 	total_scalarization fails.
> 
> testsuite/
> 	* gcc.dg/tree-ssa/pr69355.c: New test.
> 
> ---
>  gcc/testsuite/gcc.dg/tree-ssa/pr69355.c | 44 +++++++++++++++++++++++++++++++++
>  gcc/tree-sra.c                          |  2 +-
>  2 files changed, 45 insertions(+), 1 deletion(-)
>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr69355.c
> 
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr69355.c b/gcc/testsuite/gcc.dg/tree-ssa/pr69355.c
> new file mode 100644
> index 0000000..f515c21
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr69355.c
> @@ -0,0 +1,44 @@
> +/* { dg-do run } */
> +/* { dg-options "-O -fno-strict-aliasing" } */
> +
> +struct S
> +{
> +  void *a;
> +  long double b;
> +};
> +
> +struct Z
> +{
> +  long long l;
> +  short s;
> +} __attribute__((packed));
> +
> +struct S __attribute__((noclone, noinline))
> +foo (void *v, struct Z *z)
> +{
> +  struct S t;
> +  t.a = v;
> +  *(struct Z *) &t.b = *z;
> +  return t;
> +}
> +
> +struct Z gz;
> +
> +int
> +main (int argc, char **argv)
> +{
> +  struct S s;
> +
> +  if (sizeof (long double) < sizeof (struct Z))
> +    return 0;
> +
> +  gz.l = 0xbeef;
> +  gz.s = 0xab;
> +
> +  s = foo ((void *) 0, &gz);
> +
> +  if ((((struct Z *) &s.b)->l != gz.l)
> +      || (((struct Z *) &s.b)->s != gz.s))
> +    __builtin_abort ();
> +  return 0;
> +}
> diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
> index 740542f..b0e737a 100644
> --- a/gcc/tree-sra.c
> +++ b/gcc/tree-sra.c
> @@ -2421,7 +2421,7 @@ analyze_access_subtree (struct access *root, struct access *parent,
>  
>        if (covered_to < limit)
>  	hole = true;
> -      if (scalar)
> +      if (scalar || !allow_replacements)
>  	root->grp_total_scalarization = 0;
>      }
>  
>