Remove gimple_static_chain test disabling modref in ref_maybe_used_in_call_p

  Hi,
this patch removes test for function not having call chain guarding
modref use in ref_maybe_used_by_call_p_1.  It never made sense since
modref treats call chain accesses explicitly. It was however copied from
earlier check for ECF_CONST (which seems dubious too, but I would like
to discuss it independelty).

This enables us to detect that memory pointed to static chain (or parts of it)
are unused by the function.

lto-bootstrapped-regtested all lanugages on x86_64-linux. OK?

gcc/ChangeLog:

2021-11-19  Jan Hubicka  <hubicka@ucw.cz>

	* tree-ssa-alias.c (ref_maybe_used_by_call_p_1): Do not guard modref
	by !gimple_call_chain.

gcc/testsuite/ChangeLog:

2021-11-19  Jan Hubicka  <hubicka@ucw.cz>

	* gcc.dg/tree-ssa/modref-dse-6.c: New test.
  

On Fri, 19 Nov 2021, Jan Hubicka wrote:

> Hi,
> this patch removes test for function not having call chain guarding
> modref use in ref_maybe_used_by_call_p_1.  It never made sense since
> modref treats call chain accesses explicitly. It was however copied from
> earlier check for ECF_CONST (which seems dubious too, but I would like
> to discuss it independelty).
> 
> This enables us to detect that memory pointed to static chain (or parts of it)
> are unused by the function.
> 
> lto-bootstrapped-regtested all lanugages on x86_64-linux. OK?

OK.

> gcc/ChangeLog:
> 
> 2021-11-19  Jan Hubicka  <hubicka@ucw.cz>
> 
> 	* tree-ssa-alias.c (ref_maybe_used_by_call_p_1): Do not guard modref
> 	by !gimple_call_chain.
> 
> gcc/testsuite/ChangeLog:
> 
> 2021-11-19  Jan Hubicka  <hubicka@ucw.cz>
> 
> 	* gcc.dg/tree-ssa/modref-dse-6.c: New test.
> 
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/modref-dse-6.c b/gcc/testsuite/gcc.dg/tree-ssa/modref-dse-6.c
> new file mode 100644
> index 00000000000..d1e45a893ad
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/modref-dse-6.c
> @@ -0,0 +1,23 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized"  } */
> +int
> +main()
> +{
> +  int a,b;
> +  __attribute__ ((noinline))
> +  void kill_me()
> +  {
> +    a=1234;
> +    b=2234;
> +  }
> +  a=0;
> +  b=1234;
> +  __attribute__ ((noinline))
> +  int reta()
> +  {
> +    return a;
> +  }
> +  return reta();
> +}
> +/* { dg-final { scan-tree-dump-not "kill_me" "optimized" } } */
> +/* { dg-final { scan-tree-dump-not "1234" "optimized" } } */
> diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
> index 02bbc87b597..cd6a0b2f67b 100644
> --- a/gcc/tree-ssa-alias.c
> +++ b/gcc/tree-ssa-alias.c
> @@ -2755,7 +2755,7 @@ ref_maybe_used_by_call_p_1 (gcall *call, ao_ref *ref, bool tbaa_p)
>  
>    callee = gimple_call_fndecl (call);
>  
> -  if (!gimple_call_chain (call) && callee != NULL_TREE)
> +  if (callee != NULL_TREE)
>      {
>        struct cgraph_node *node = cgraph_node::get (callee);
>        /* We can not safely optimize based on summary of calle if it does
>