On Sat, Nov 12, 2016 at 9:31 AM, Segher Boessenkool
<seg...@kernel.crashing.org> wrote:
> So far all target implementations of the separate shrink-wrapping hooks
> use the DF LIVE info to figure out around which basic blocks the non-
> volatile registers need to be saved. This is done by looking at the
> IN+GEN+KILL sets of the basic blocks. However, that doesn't work for
> registers that DF says are defined in the entry block, or used in the
> exit block.
>
> This patch introduces a shrink_wrap_separate_in_progress variable, and
> makes df_get_entry_block_def_set and df_get_exit_block_use_set set the
> respective sets to empty if that variable is set to true. It also
> changes the rs6000 port to use IN+GEN+KILL for the LR component.
>
> [ <https://gcc.gnu.org/ml/gcc-patches/2016-08/msg01986.html> is an older
> version of this, using a different (much inferior) approach. ]
>
> Tested on powerpc64-linux {-m32,-m64}. Is this okay for trunk?
Globals like this are somewhat gross. There are df_changeable_flags
where we seem to have a "related" flag DF_RD_PRUNE_DEAD_DEFS
so you could add a flag for this. There's also local_flags (only used
by df_chain_add_problem).
Richard.
>
> Segher
>
>
> 2016-11-12 Segher Boessenkool <seg...@kernel.crashing.org>
>
> * config/rs6000/rs6000.c (rs6000_components_for_bb): Mark the LR
> component as used also if LR_REGNO is a live input to the bb.
> * df-scan.c (df_get_entry_block_def_set): Return immediately after
> clearing the set if shrink_wrap_separate_in_progress.
> (df_get_exit_block_use_set): Ditto.
> * rtl.h (shrink_wrap_separate_in_progress): Declare new variable.
> * shrink-wrap.c (shrink_wrap_separate_in_progress): New variable.
> (try_shrink_wrapping_separate): Set shrink_wrap_separate_in_progress
> and call df_update_entry_block_defs and df_update_exit_block_uses
> at the start; clear that variable and call those functions at the end.
>
> ---
> gcc/config/rs6000/rs6000.c | 3 ++-
> gcc/df-scan.c | 16 ++++++++++++++++
> gcc/rtl.h | 3 +++
> gcc/shrink-wrap.c | 12 ++++++++++++
> 4 files changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> index 49985f1..8d6b2d5 100644
> --- a/gcc/config/rs6000/rs6000.c
> +++ b/gcc/config/rs6000/rs6000.c
> @@ -27714,7 +27714,8 @@ rs6000_components_for_bb (basic_block bb)
> bitmap_set_bit (components, regno);
>
> /* LR needs to be saved around a bb if it is killed in that bb. */
> - if (bitmap_bit_p (gen, LR_REGNO)
> + if (bitmap_bit_p (in, LR_REGNO)
> + || bitmap_bit_p (gen, LR_REGNO)
> || bitmap_bit_p (kill, LR_REGNO))
> bitmap_set_bit (components, 0);
>
> diff --git a/gcc/df-scan.c b/gcc/df-scan.c
> index 7cfd34b..398842b 100644
> --- a/gcc/df-scan.c
> +++ b/gcc/df-scan.c
> @@ -3506,6 +3506,14 @@ df_get_entry_block_def_set (bitmap entry_block_defs)
>
> bitmap_clear (entry_block_defs);
>
> + /* For separate shrink-wrapping we use LIVE to analyze which basic blocks
> + need a prologue for some component to be executed before that block,
> + and we do not care about any other registers. Hence, we do not want
> + any register for any component defined in the entry block, and we can
> + just leave all registers undefined. */
> + if (shrink_wrap_separate_in_progress)
> + return;
> +
> for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
> {
> if (global_regs[i])
> @@ -3665,6 +3673,14 @@ df_get_exit_block_use_set (bitmap exit_block_uses)
>
> bitmap_clear (exit_block_uses);
>
> + /* For separate shrink-wrapping we use LIVE to analyze which basic blocks
> + need an epilogue for some component to be executed after that block,
> + and we do not care about any other registers. Hence, we do not want
> + any register for any component seen as used in the exit block, and we
> + can just say no registers at all are used. */
> + if (shrink_wrap_separate_in_progress)
> + return;
> +
> /* Stack pointer is always live at the exit. */
> bitmap_set_bit (exit_block_uses, STACK_POINTER_REGNUM);
>
> diff --git a/gcc/rtl.h b/gcc/rtl.h
> index 3bb6a22..d1409bc 100644
> --- a/gcc/rtl.h
> +++ b/gcc/rtl.h
> @@ -3468,6 +3468,9 @@ extern int lra_in_progress;
>
> #define can_create_pseudo_p() (!reload_in_progress && !reload_completed)
>
> +/* Set to true during separate shrink-wrapping. */
> +extern bool shrink_wrap_separate_in_progress;
> +
> #ifdef STACK_REGS
> /* Nonzero after end of regstack pass.
> Set to 1 or 0 by reg-stack.c. */
> diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c
> index e480d4d..dd0cae1 100644
> --- a/gcc/shrink-wrap.c
> +++ b/gcc/shrink-wrap.c
> @@ -1764,6 +1764,10 @@ insert_prologue_epilogue_for_components (sbitmap
> components)
> commit_edge_insertions ();
> }
>
> +/* Used by DF: if true, the entry block defines no registers, and the exit
> + block uses none. */
> +bool shrink_wrap_separate_in_progress = false;
> +
> /* The main entry point to this subpass. FIRST_BB is where the prologue
> would be normally put. */
> void
> @@ -1794,6 +1798,9 @@ try_shrink_wrapping_separate (basic_block first_bb)
> return;
>
> /* We need LIVE info. */
> + shrink_wrap_separate_in_progress = true;
> + df_update_entry_block_defs ();
> + df_update_exit_block_uses ();
> df_live_add_problem ();
> df_live_set_all_dirty ();
> df_analyze ();
> @@ -1859,6 +1866,11 @@ try_shrink_wrapping_separate (basic_block first_bb)
> free_dominance_info (CDI_DOMINATORS);
> free_dominance_info (CDI_POST_DOMINATORS);
>
> + /* All done. */
> + shrink_wrap_separate_in_progress = false;
> + df_update_entry_block_defs ();
> + df_update_exit_block_uses ();
> +
> if (crtl->shrink_wrapped_separate)
> {
> df_live_set_all_dirty ();
> --
> 1.9.3
>
