On Fri, Sep 24, 2021 at 8:29 AM Xionghu Luo <luo...@linux.ibm.com> wrote:
>
> Update the patch to v3, not sure whether you prefer the paste style
> and continue to link the previous thread as Segher dislikes this...
>
>
> [PATCH v3] Don't move cold code out of loop by checking bb count
>
>
> Changes:
> 1. Handle max_loop in determine_max_movement instead of
> outermost_invariant_loop.
> 2. Remove unnecessary changes.
> 3. Add for_all_locs_in_loop (loop, ref, ref_in_loop_hot_body) in can_sm_ref_p.
> 4. "gsi_next (&bsi);" in move_computations_worker is kept since it caused
> infinite loop when implementing v1 and the iteration is missed to be
> updated actually.
>
> v1: https://gcc.gnu.org/pipermail/gcc-patches/2021-August/576488.html
> v2: https://gcc.gnu.org/pipermail/gcc-patches/2021-September/579086.html
>
> There was a patch trying to avoid move cold block out of loop:
>
> https://gcc.gnu.org/pipermail/gcc/2014-November/215551.html
>
> Richard suggested to "never hoist anything from a bb with lower execution
> frequency to a bb with higher one in LIM invariantness_dom_walker
> before_dom_children".
>
> In gimple LIM analysis, add find_coldest_out_loop to move invariants to
> expected target loop, if profile count of the loop bb is colder
> than target loop preheader, it won't be hoisted out of loop.
> Likely for store motion, if all locations of the REF in loop is cold,
> don't do store motion of it.
>
> SPEC2017 performance evaluation shows 1% performance improvement for
> intrate GEOMEAN and no obvious regression for others. Especially,
> 500.perlbench_r +7.52% (Perf shows function S_regtry of perlbench is
> largely improved.), and 548.exchange2_r+1.98%, 526.blender_r +1.00%
> on P8LE.
>
> gcc/ChangeLog:
>
> * loop-invariant.c (find_invariants_bb): Check profile count
> before motion.
> (find_invariants_body): Add argument.
> * tree-ssa-loop-im.c (find_coldest_out_loop): New function.
> (determine_max_movement): Use find_coldest_out_loop.
> (move_computations_worker): Adjust and fix iteration udpate.
> (execute_sm_exit): Check pointer validness.
> (class ref_in_loop_hot_body): New functor.
> (ref_in_loop_hot_body::operator): New.
> (can_sm_ref_p): Use for_all_locs_in_loop.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/tree-ssa/recip-3.c: Adjust.
> * gcc.dg/tree-ssa/ssa-lim-18.c: New test.
> * gcc.dg/tree-ssa/ssa-lim-19.c: New test.
> * gcc.dg/tree-ssa/ssa-lim-20.c: New test.
> ---
> gcc/loop-invariant.c | 10 ++--
> gcc/tree-ssa-loop-im.c | 61 ++++++++++++++++++++--
> gcc/testsuite/gcc.dg/tree-ssa/recip-3.c | 2 +-
> gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-18.c | 20 +++++++
> gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-19.c | 27 ++++++++++
> gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-20.c | 25 +++++++++
> gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-21.c | 28 ++++++++++
> 7 files changed, 165 insertions(+), 8 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-18.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-19.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-20.c
> create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-21.c
>
> diff --git a/gcc/loop-invariant.c b/gcc/loop-invariant.c
> index fca0c2b24be..5c3be7bf0eb 100644
> --- a/gcc/loop-invariant.c
> +++ b/gcc/loop-invariant.c
> @@ -1183,9 +1183,14 @@ find_invariants_insn (rtx_insn *insn, bool
> always_reached, bool always_executed)
> call. */
>
> static void
> -find_invariants_bb (basic_block bb, bool always_reached, bool
> always_executed)
> +find_invariants_bb (class loop *loop, basic_block bb, bool always_reached,
> + bool always_executed)
> {
> rtx_insn *insn;
> + basic_block preheader = loop_preheader_edge (loop)->src;
> +
> + if (preheader->count > bb->count)
> + return;
>
> FOR_BB_INSNS (bb, insn)
> {
> @@ -1214,8 +1219,7 @@ find_invariants_body (class loop *loop, basic_block
> *body,
> unsigned i;
>
> for (i = 0; i < loop->num_nodes; i++)
> - find_invariants_bb (body[i],
> - bitmap_bit_p (always_reached, i),
> + find_invariants_bb (loop, body[i], bitmap_bit_p (always_reached, i),
> bitmap_bit_p (always_executed, i));
> }
>
> diff --git a/gcc/tree-ssa-loop-im.c b/gcc/tree-ssa-loop-im.c
> index 4b187c2cdaf..655fab03442 100644
> --- a/gcc/tree-ssa-loop-im.c
> +++ b/gcc/tree-ssa-loop-im.c
> @@ -417,6 +417,28 @@ movement_possibility (gimple *stmt)
> return ret;
> }
>
> +/* Find coldest loop between outmost_loop and loop by comapring profile
> count. */
> +
> +static class loop *
> +find_coldest_out_loop (class loop *outmost_loop, class loop *loop,
> + basic_block curr_bb)
> +{
> + class loop *cold_loop, *min_loop;
> + cold_loop = min_loop = outmost_loop;
> + profile_count min_count = loop_preheader_edge (min_loop)->src->count;
> +
> + if (curr_bb && curr_bb->count < loop_preheader_edge (loop)->src->count)
Honza - can you comment on whether we should compare BB counts this way?
I would suspect that for, say,
for (...)
if (a)
X;
else
Y;
that the counts for X and Y will be less than that of the preheader of the loop
only when the loop is estimated to run once. That is, should we really compare
the to the preheader count or maybe better to the _header_ count which
would keep the number of iterations out of the equation?
If we look at maybe_hot_count_p that's a quite sophisticated thing to
compare a count to the "IPA hot", here we're comparing two counts
within a function where it actually matters whether we use a<b or
!(a>=b) since 'unordered' is mapped to false (but there's no ordered_p
function).
Xionghu, you error on the side of not hoisting for unordered counts here
> + return NULL;
> +
> + while (min_loop != loop)
> + {
> + min_loop = superloop_at_depth (loop, loop_depth (min_loop) + 1);
> + if (loop_preheader_edge (min_loop)->src->count < min_count)
but in the other direction here and on the side of not hoisting
in ref_in_loop_hot_body.
The three-state relational operator overloads are probably not the
very best idea...
(see profile-count.h for them)
> + cold_loop = min_loop;
> + }
> + return cold_loop;
> +}
> +
> /* Suppose that operand DEF is used inside the LOOP. Returns the outermost
> loop to that we could move the expression using DEF if it did not have
> other operands, i.e. the outermost loop enclosing LOOP in that the value
> @@ -685,7 +707,9 @@ determine_max_movement (gimple *stmt, bool
> must_preserve_exec)
> level = ALWAYS_EXECUTED_IN (bb);
> else
> level = superloop_at_depth (loop, 1);
> - lim_data->max_loop = level;
> + lim_data->max_loop = find_coldest_out_loop (level, loop, bb);
> + if (!lim_data->max_loop)
> + return false;
>
> if (gphi *phi = dyn_cast <gphi *> (stmt))
> {
> @@ -1198,7 +1222,6 @@ move_computations_worker (basic_block bb)
> for (gimple_stmt_iterator bsi = gsi_start_bb (bb); !gsi_end_p (bsi); )
> {
> edge e;
> -
> gimple *stmt = gsi_stmt (bsi);
>
> lim_data = get_lim_data (stmt);
> @@ -1221,7 +1244,10 @@ move_computations_worker (basic_block bb)
> /* We do not really want to move conditionals out of the loop; we just
> placed it here to force its operands to be moved if necessary. */
> if (gimple_code (stmt) == GIMPLE_COND)
> - continue;
> + {
> + gsi_next (&bsi);
> + continue;
> + }
>
> if (dump_file && (dump_flags & TDF_DETAILS))
> {
> @@ -2241,7 +2267,12 @@ execute_sm_exit (class loop *loop, edge ex,
> vec<seq_entry> &seq,
> }
> else
> {
> - sm_aux *aux = *aux_map.get (ref);
> + sm_aux **paux = aux_map.get (ref);
> + sm_aux *aux;
> + if (paux)
> + aux = *paux;
> + else
> + continue;
do you really need this? I doubt so.
> if (!aux->store_flag || kind == sm_ord)
> {
> gassign *store;
> @@ -2887,6 +2918,25 @@ ref_indep_loop_p (class loop *loop, im_mem_ref *ref,
> dep_kind kind)
> return indep_p;
> }
>
> +class ref_in_loop_hot_body
> +{
> +public:
> + ref_in_loop_hot_body (loop *loop_) : l (loop_) {}
> + bool operator () (mem_ref_loc *loc);
> + class loop *l;
> +};
> +
> +bool
> +ref_in_loop_hot_body::operator () (mem_ref_loc *loc)
> +{
> + basic_block curr_bb = gimple_bb (loc->stmt);
> + edge e = loop_preheader_edge (l);
> + if (e->src->count > curr_bb->count)
> + return false;
> + else
> + return true;
> +}
> +
>
> /* Returns true if we can perform store motion of REF from LOOP. */
>
> @@ -2941,6 +2991,9 @@ can_sm_ref_p (class loop *loop, im_mem_ref *ref)
> if (!ref_indep_loop_p (loop, ref, sm_war))
> return false;
>
Add a comment here what this is about.
Otherwise the GIMPLE invariant motion parts look sensible, but I'd
really like to have
the issue on the profile_count API sorted out.
Can you split out the RTL invariant motion part to a separate patch please?
Thanks,
Richard.
> + if (!for_all_locs_in_loop (loop, ref, ref_in_loop_hot_body (loop)))
> + return false;
> +
> return true;
> }
>
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> b/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> index 638bf38db8c..641c91e719e 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/recip-3.c
> @@ -23,4 +23,4 @@ float h ()
> F[0] += E / d;
> }
>
> -/* { dg-final { scan-tree-dump-times " / " 1 "recip" } } */
> +/* { dg-final { scan-tree-dump-times " / " 5 "recip" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-18.c
> b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-18.c
> new file mode 100644
> index 00000000000..7326a230b3f
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-18.c
> @@ -0,0 +1,20 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-lim2-details" } */
> +
> +volatile int x;
> +void
> +bar (int, char *, char *);
> +void
> +foo (int *a, int n, int k)
> +{
> + int i;
> +
> + for (i = 0; i < n; i++)
> + {
> + if (__builtin_expect (x, 0))
> + bar (k / 5, "one", "two");
> + a[i] = k;
> + }
> +}
> +
> +/* { dg-final { scan-tree-dump-not "out of loop 1" "lim2" } } */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-19.c
> b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-19.c
> new file mode 100644
> index 00000000000..f0a99fa42b4
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-19.c
> @@ -0,0 +1,27 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-lim2-details" } */
> +
> +volatile int x;
> +void
> +bar (int, char *, char *);
> +void
> +foo (int *a, int n, int m, int k, int s)
> +{
> + int i;
> + int j;
> +
> + for (i = 0; i < m; i++)
> + {
> + if (__builtin_expect (x, 0))
> + for (j = 0; j < n; j++)
> + {
> + bar (k / 5, "one", "two");
> + a[s] = k;
> + }
> + a[s] = s;
> + }
> +}
> +
> +/* { dg-final { scan-tree-dump-times "out of loop 2" 4 "lim2" } } */
> +/* { dg-final { scan-tree-dump-times "out of loop 1" 3 "lim2" } } */
> +
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-20.c
> b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-20.c
> new file mode 100644
> index 00000000000..bc60a040a70
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-20.c
> @@ -0,0 +1,25 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-lim2-details" } */
> +
> +/* Test that `count' is not hoisted out of loop when bb is cold. */
> +
> +int count;
> +volatile int x;
> +
> +struct obj {
> + int data;
> + struct obj *next;
> +
> +} *q;
> +
> +void
> +func (int m)
> +{
> + struct obj *p;
> + for (int i = 0; i < m; i++)
> + if (__builtin_expect (x, 0))
> + count++;
> +
> +}
> +
> +/* { dg-final { scan-tree-dump-not "Executing store motion of" "lim2" } }
> */
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-21.c
> b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-21.c
> new file mode 100644
> index 00000000000..fedaa3b7119
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-21.c
> @@ -0,0 +1,28 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-lim2-details" } */
> +
> +/* Test that `count' is hoisted out of loop when one of it's used bb is hot.
> */
> +
> +int count;
> +volatile int x;
> +
> +struct obj {
> + int data;
> + struct obj *next;
> +
> +} *q;
> +
> +void
> +func (int m, int n)
> +{
> + struct obj *p;
> + for (int i = 0; i < m; i++)
> + {
> + if (__builtin_expect (x, 0))
> + count++;
> + count += n;
> + }
> +}
> +
> +/* { dg-final { scan-tree-dump-times "Executing store motion of" 1 "lim2" }
> } */
> +
> --
> 2.27.0.90.geebb51ba8c
>
>
