Re: [PATCH 1/3] gimple-fold: Transform stp*cpy_chk to str*cpy directly

[Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org>]

On Fri, 12 Nov 2021 at 01:12, Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>
> Avoid going through another folding cycle and use the ignore flag to
> directly transform BUILT_IN_STPCPY_CHK to BUILT_IN_STRCPY when set,
> likewise for BUILT_IN_STPNCPY_CHK to BUILT_IN_STPNCPY.
>
> Dump the transformation in dump_file so that we can verify in tests that
> the direct transformation actually happened.
>
> gcc/ChangeLog:
>
>         * gimple-fold.c (gimple_fold_builtin_stxcpy_chk,
>         gimple_fold_builtin_stxncpy_chk): Use BUILT_IN_STRNCPY if return
>         value is not used.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.dg/fold-stringops.c: New test.
>
> Signed-off-by: Siddhesh Poyarekar <siddhesh@gotplt.org>
> ---
>  gcc/gimple-fold.c                       | 50 +++++++++++++++++--------
>  gcc/testsuite/gcc.dg/fold-stringops-1.c | 23 ++++++++++++
>  2 files changed, 57 insertions(+), 16 deletions(-)
>  create mode 100644 gcc/testsuite/gcc.dg/fold-stringops-1.c
>
> diff --git a/gcc/gimple-fold.c b/gcc/gimple-fold.c
> index 6e25a7c05db..92e15784803 100644
> --- a/gcc/gimple-fold.c
> +++ b/gcc/gimple-fold.c
> @@ -3088,6 +3088,19 @@ gimple_fold_builtin_memory_chk (gimple_stmt_iterator *gsi,
>    return true;
>  }
>
> +static void
> +dump_transformation (gimple *from, gimple *to)
I assume that both from and to will always be builtin calls ?
In that case, perhaps better to use gcall * here (and in rest of patch).
Also, needs a top-level comment describing the function.
> +{
> +  if (dump_file && (dump_flags & TDF_DETAILS))
Perhaps better to use dump_enabled_p ?
> +    {
> +      fprintf (dump_file, "transformed ");
Perhaps use dump_printf_loc (MSG_OPTIMIZED_LOCATIONS, ...) ?
I think you can use gimple_location to get the location.

Thanks,
Prathamesh
> +      print_generic_expr (dump_file, gimple_call_fn (from), dump_flags);
> +      fprintf (dump_file, " to ");
> +      print_generic_expr (dump_file, gimple_call_fn (to), dump_flags);
> +      fprintf (dump_file, "\n");
> +    }
> +}
> +
>  /* Fold a call to the __st[rp]cpy_chk builtin.
>     DEST, SRC, and SIZE are the arguments to the call.
>     IGNORE is true if return value can be ignored.  FCODE is the BUILT_IN_*
> @@ -3184,12 +3197,13 @@ gimple_fold_builtin_stxcpy_chk (gimple_stmt_iterator *gsi,
>      }
>
>    /* If __builtin_st{r,p}cpy_chk is used, assume st{r,p}cpy is available.  */
> -  fn = builtin_decl_explicit (fcode == BUILT_IN_STPCPY_CHK
> +  fn = builtin_decl_explicit (fcode == BUILT_IN_STPCPY_CHK && !ignore
>                               ? BUILT_IN_STPCPY : BUILT_IN_STRCPY);
>    if (!fn)
>      return false;
>
>    gimple *repl = gimple_build_call (fn, 2, dest, src);
> +  dump_transformation (stmt, repl);
>    replace_call_with_call_and_fold (gsi, repl);
>    return true;
>  }
> @@ -3209,19 +3223,6 @@ gimple_fold_builtin_stxncpy_chk (gimple_stmt_iterator *gsi,
>    bool ignore = gimple_call_lhs (stmt) == NULL_TREE;
>    tree fn;
>
> -  if (fcode == BUILT_IN_STPNCPY_CHK && ignore)
> -    {
> -       /* If return value of __stpncpy_chk is ignored,
> -          optimize into __strncpy_chk.  */
> -       fn = builtin_decl_explicit (BUILT_IN_STRNCPY_CHK);
> -       if (fn)
> -        {
> -          gimple *repl = gimple_build_call (fn, 4, dest, src, len, size);
> -          replace_call_with_call_and_fold (gsi, repl);
> -          return true;
> -        }
> -    }
> -
>    if (! tree_fits_uhwi_p (size))
>      return false;
>
> @@ -3234,7 +3235,23 @@ gimple_fold_builtin_stxncpy_chk (gimple_stmt_iterator *gsi,
>              For MAXLEN only allow optimizing into non-_ocs function
>              if SIZE is >= MAXLEN, never convert to __ocs_fail ().  */
>           if (maxlen == NULL_TREE || ! tree_fits_uhwi_p (maxlen))
> -           return false;
> +           {
> +             if (fcode == BUILT_IN_STPNCPY_CHK && ignore)
> +               {
> +                 /* If return value of __stpncpy_chk is ignored,
> +                    optimize into __strncpy_chk.  */
> +                 fn = builtin_decl_explicit (BUILT_IN_STRNCPY_CHK);
> +                 if (fn)
> +                   {
> +                     gimple *repl = gimple_build_call (fn, 4, dest, src, len,
> +                                                       size);
> +                     replace_call_with_call_and_fold (gsi, repl);
> +                     return true;
> +                   }
> +               }
> +
> +             return false;
> +           }
>         }
>        else
>         maxlen = len;
> @@ -3244,12 +3261,13 @@ gimple_fold_builtin_stxncpy_chk (gimple_stmt_iterator *gsi,
>      }
>
>    /* If __builtin_st{r,p}ncpy_chk is used, assume st{r,p}ncpy is available.  */
> -  fn = builtin_decl_explicit (fcode == BUILT_IN_STPNCPY_CHK
> +  fn = builtin_decl_explicit (fcode == BUILT_IN_STPNCPY_CHK && !ignore
>                               ? BUILT_IN_STPNCPY : BUILT_IN_STRNCPY);
>    if (!fn)
>      return false;
>
>    gimple *repl = gimple_build_call (fn, 3, dest, src, len);
> +  dump_transformation (stmt, repl);
>    replace_call_with_call_and_fold (gsi, repl);
>    return true;
>  }
> diff --git a/gcc/testsuite/gcc.dg/fold-stringops-1.c b/gcc/testsuite/gcc.dg/fold-stringops-1.c
> new file mode 100644
> index 00000000000..712dd369e7c
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/fold-stringops-1.c
> @@ -0,0 +1,23 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-lower-details" } */
> +
> +char dst[2048];
> +
> +char *
> +copy1 (const char *src, int cond)
> +{
> +  __builtin___stpncpy_chk (dst, src, 42, __builtin_object_size (dst, 0));
> +
> +  return dst;
> +}
> +
> +char *
> +copy2 (void)
> +{
> +  __builtin___stpcpy_chk (dst, "Hello world", __builtin_object_size (dst, 0));
> +
> +  return dst;
> +}
> +/* { dg-final { scan-tree-dump "transformed __builtin___stpncpy_chk to __builtin_strncpy" "lower" } } */
> +/* { dg-final { scan-tree-dump "transformed __builtin___stpcpy_chk to __builtin_strcpy" "lower" } } */
> +
> --
> 2.31.1
>