Qing Zhao <qing.z...@oracle.com> writes:
> Hi, Richard,
>
> Could you please review this patch? This is a fix to the previous
> -fzero-call-used-regs implementation.
>
> PR 100775 ( ICE: in df_exit_block_bitmap_verify, at df-scan.c:4164 with
> -mthumb -fzero-call-used-regs=used)
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100775
>
> Although the ICE only happens on arm, but this is a bug in the middle end.
> So, I think this bug has higher priority,
> Need to be included into gcc12, and also need to be back ported to gcc11.
>
> In the pass_zero_call_used_regs, when updating dataflow info after adding
> the register zeroing sequence in the epilogue of the function, we should
> call "df_update_exit_block_uses" to update the register use information in
> the exit block to include all the registers that have been zeroed.
>
> The change has been bootstrapped and reg-tested on both x86 and aarch64 (with
> -enable-checking=yes,rtl,df).
> Since I cannot find an arm machine, no bootstrap and reg-tested on arm yet.
>
> For the arm failure, I just tested it with the cross build and it has no
> issue withe the fix.
>
> (One question here:
> Previously, I though “df_set_bb_dirty (EXIT_BLOCK_PTR_FOR_FN (cfun))” and a
> later “df_analyze()” should rescan
> the changed exit block of the function, and update all the df info
> automatically, it apparently not the case, the register
> use info at exit block is not automatically updated, we have to add an
> explicitly call to “df_update_exit_block_uses”.
> I checked the pass_thread_prologue_and_epilogue, looks like it also
> explicitly calls “df_update_entry_exit_and_calls”
> to update the register use info.
> Shall the “df_set_bb_dirty” + “df_analyze” automatically update the reg use
> info of the dirty block?).
I think the current df behaviour makes sense. Updating the set of
live-out registers is a specialised operation and I think it's better
to make it explicit.
>
> Let me know whether there is any issue with the fix?
>
> Thanks
>
> Qing
>
> ===================================
>
> From e1cca5659c85e7c536f5016a2c75c615e65dba75 Mon Sep 17 00:00:00 2001
> From: Qing Zhao <qing.z...@oracle.com>
> Date: Fri, 28 Jan 2022 16:29:51 +0000
> Subject: [PATCH] middle-end: updating the reg use in exit block for
> -fzero-call-used-regs [PR100775]
>
> In the pass_zero_call_used_regs, when updating dataflow info after adding
> the register zeroing sequence in the epilogue of the function, we should
> call "df_update_exit_block_uses" to update the register use information in
> the exit block to include all the registers that have been zeroed.
>
> 2022-01-27 Qing Zhao <qing.z...@oracle.com>
>
> gcc/ChangeLog:
>
> * function.cc (gen_call_used_regs_seq): Call
> df_update_exit_block_uses when updating df.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/arm/pr100775.c: New test.
> ---
> gcc/function.cc | 1 +
> gcc/testsuite/gcc.target/arm/pr100775.c | 8 ++++++++
> 2 files changed, 9 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/arm/pr100775.c
>
> diff --git a/gcc/function.cc b/gcc/function.cc
> index e1d2565f8d92..c8a77c9a6246 100644
> --- a/gcc/function.cc
> +++ b/gcc/function.cc
> @@ -5942,6 +5942,7 @@ gen_call_used_regs_seq (rtx_insn *ret, unsigned int
> zero_regs_type)
> /* Update the data flow information. */
> crtl->must_be_zero_on_return |= zeroed_hardregs;
> df_set_bb_dirty (EXIT_BLOCK_PTR_FOR_FN (cfun));
> + df_update_exit_block_uses ();
I think this should replace the df_set_bb_dirty call:
df_update_exit_block_uses will mark the block as dirty where
necessary.
Nit, but the indentation of the new call looks off.
> }
> }
>
> diff --git a/gcc/testsuite/gcc.target/arm/pr100775.c
> b/gcc/testsuite/gcc.target/arm/pr100775.c
> new file mode 100644
> index 000000000000..dd2255a95492
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/arm/pr100775.c
> @@ -0,0 +1,8 @@
> +/* { dg-do compile } */
Please add:
/* { dg-skip-if "" { ! { arm_thumb1_ok || arm_thumb2_ok } } } */
here.
OK with those changes, thanks. Please wait a week or so before
backporting.
Richard
> +/* { dg-options "-mthumb -fzero-call-used-regs=used" } */
> +
> +int
> +foo (int x)
> +{
> + return x;
> +}
