On Tue, Jul 25, 2023 at 1:49 AM Andrew Pinski via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> In this case we are not removing convert to a bigger size
> back to the same size (or smaller) if signedness does not
> match.
> For an example:
> ```
> signed char _1;
> ...
> _1 = *a_4(D);
> b_5 = (short unsigned int) _1;
> _2 = (unsigned char) b_5;
> ```
> The inner cast is not needed and can be removed but was not.
> The match pattern for removing the extra cast is overly
> complex so decided to add a new case for rather than trying
> to modify the current if statement here.
>
> OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.
>
> gcc/ChangeLog:
>
> * match.pd (nested int casts): A truncation (to the same size or
> smaller)
> can always remove the inner cast.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/cast-1.c: New test.
> * gcc.dg/tree-ssa/cast-2.c: New test.
> ---
> gcc/match.pd | 10 ++++++++++
> gcc/testsuite/gcc.dg/tree-ssa/cast-1.c | 12 ++++++++++++
> gcc/testsuite/gcc.dg/tree-ssa/cast-2.c | 12 ++++++++++++
> 3 files changed, 34 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cast-1.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cast-2.c
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index bfd15d6cd4a..bc8a3ab17eb 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -4257,6 +4257,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> && ! (final_ptr && inside_prec != inter_prec))
> (ocvt @0))
>
> + /* `(signed:M)(signed:N)(signed:O)`
> + can be convert it to `(signed:M)a`
Better say
(outer:M)(inter:N) a:O
can be converted to (outer:M) a
since as you say below the signedness doesn't really matter and this
would then also mention 'a'
> + if M <= O && N >= O. No matter what signedness of the cast,
of the casts
OK with those comment changes.
Thanks,
Richard.
> + as the final is either a truncation from the original or just
> + a sign change of the type. */
> + (if (inside_int && inter_int && final_int
> + && final_prec <= inside_prec
> + && inter_prec >= inside_prec)
> + (convert @0))
> +
> /* A truncation to an unsigned type (a zero-extension) should be
> canonicalized as bitwise and of a mask. */
> (if (GIMPLE /* PR70366: doing this in GENERIC breaks -Wconversion. */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/cast-1.c
> b/gcc/testsuite/gcc.dg/tree-ssa/cast-1.c
> new file mode 100644
> index 00000000000..0f33ab58b3e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/cast-1.c
> @@ -0,0 +1,12 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-optimized" } */
> +
> +
> +void f(signed char *a, unsigned char *c)
> +{
> + unsigned short b = *a;
> + *c = ((unsigned char)b);
> +}
> +
> +
> +/* { dg-final { scan-tree-dump-not "\\(short unsigned int\\)" "optimized"} }
> */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/cast-2.c
> b/gcc/testsuite/gcc.dg/tree-ssa/cast-2.c
> new file mode 100644
> index 00000000000..d665e924831
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/cast-2.c
> @@ -0,0 +1,12 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O1 -fdump-tree-optimized" } */
> +
> +
> +void f(signed short *a, unsigned char *c)
> +{
> + unsigned long b = *a;
> + *c = ((unsigned char)b);
> +}
> +
> +
> +/* { dg-final { scan-tree-dump-not "\\(long unsigned int\\)" "optimized"} }
> */
> --
> 2.31.1
>
