On Tue, Jun 3, 2025 at 10:51 AM Andrew Pinski <quic_apin...@quicinc.com> wrote:
>
> When we have a smallish CSWTCH, it could be placed in the rodata.cst16
> section so it can be merged with other constants across TUs.
>
> The fix is simple; just mark the decl as mergable (DECL_MERGEABLE).
> DECL_MERGEABLE was added with r14-1500-g4d935f52b0d5c0 specifically
> to improve these kind of decls.
>
> PR tree-optimization/120451
>
> gcc/ChangeLog:
>
> * tree-switch-conversion.cc (switch_conversion::build_one_array): Mark
> the newly created decl as mergable.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/cswtch-6.c: New test.
>
> Signed-off-by: Andrew Pinski <quic_apin...@quicinc.com>
> ---
> gcc/testsuite/gcc.dg/tree-ssa/cswtch-6.c | 43 ++++++++++++++++++++++++
> gcc/tree-switch-conversion.cc | 3 ++
> 2 files changed, 46 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/cswtch-6.c
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/cswtch-6.c
> b/gcc/testsuite/gcc.dg/tree-ssa/cswtch-6.c
> new file mode 100644
> index 00000000000..d765a03aa19
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/cswtch-6.c
> @@ -0,0 +1,43 @@
> +/* PR tree-optimization/120451 */
> +/* { dg-do compile { target elf } } */
> +/* { dg-options "-O2" } */
> +
> +void foo (int, int);
> +
> +__attribute__((noinline, noclone)) void
> +f1 (int v, int w)
> +{
> + int i, j;
> + if (w)
> + {
> + i = 129;
> + j = i - 1;
> + goto lab;
> + }
> + switch (v)
> + {
> + case 170:
> + j = 7;
> + i = 27;
> + break;
> + case 171:
> + i = 8;
> + j = 122;
> + break;
> + case 172:
> + i = 21;
> + j = -19;
> + break;
> + case 173:
> + i = 18;
> + j = 17;
> + break;
> + default:
> + __builtin_abort ();
> + }
> +
> + lab:
> + foo (i, j);
> +}
> +
> +/* { dg-final { scan-assembler ".rodata.cst16" } } */
> diff --git a/gcc/tree-switch-conversion.cc b/gcc/tree-switch-conversion.cc
> index bd4de966892..d0882879e61 100644
> --- a/gcc/tree-switch-conversion.cc
> +++ b/gcc/tree-switch-conversion.cc
> @@ -1030,6 +1030,9 @@ switch_conversion::build_one_array (int num, tree
> arr_index_type,
> TREE_CONSTANT (decl) = 1;
> TREE_READONLY (decl) = 1;
> DECL_IGNORED_P (decl) = 1;
> + /* The decl is mergable since we don't take the address ever and
> + just reading from it. */
> + DECL_MERGEABLE (decl) = 1;
> if (offloading_function_p (cfun->decl))
> DECL_ATTRIBUTES (decl)
> = tree_cons (get_identifier ("omp declare target"), NULL_TREE,
> --
> 2.43.0
>
On x86-64/Linux, I got
spawn -ignore SIGHUP
/export/build/gnu/tools-build/gcc-gitlab-test/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/tools-build/gcc-gitlab-test/build-x86_64-linux/gcc/
/export/gnu/import/git/gitlab/x86-gcc-test/gcc/testsuite/gcc.dg/tree-ssa/cswtch-6.c
-m32 -fdiagnostics-plain-output -O2 -ffat-lto-objects -fno-ident -S -o
cswtch-6.s
PASS: gcc.dg/tree-ssa/cswtch-6.c (test for excess errors)
FAIL: gcc.dg/tree-ssa/cswtch-6.c scan-assembler .rodata.cst16
--
H.J.
