On 2021/11/4 21:00, Richard Biener wrote:
> On Wed, Nov 3, 2021 at 2:29 PM Xionghu Luo <luo...@linux.ibm.com> wrote:
>>
>>
>>> + while (outmost_loop != loop)
>>> + {
>>> + if (bb_colder_than_loop_preheader (loop_preheader_edge
>>> (outmost_loop)->src,
>>> + loop_preheader_edge
>>> (cold_loop)->src))
>>> + cold_loop = outmost_loop;
>>> + outmost_loop = superloop_at_depth (loop, loop_depth (outmost_loop) +
>>> 1);
>>> + }
>>>
>>> could be instead written as
>>>
>>> coldest_loop = coldest_outermost_loop[loop->num];
>>> if (loop_depth (coldest_loop) < loop_depth (outermost_loop))
>>> return outermost_loop;
>>> return coldest_loop;
>>>
>>> ? And in the usual case coldest_outermost_loop[L] would be the loop tree
>>> root.
>>> It should be possible to compute such cache in a DFS walk of the loop tree
>>> (the loop iterator by default visits in such order).
>>
>>
>> Thanks. Updated the patch with your suggestion. Not sure whether it
>> strictly
>> conforms to your comments. Though the patch passed all my added
>> tests(coverage not enough),
>> I am still a bit worried if pre-computed coldest_loop is outside of
>> outermost_loop, but
>> outermost_loop is not the COLDEST LOOP, i.e. (outer->inner)
>>
>> [loop tree root, coldest_loop, outermost_loop,..., second_coldest_loop,
>> ..., loop],
>>
>> then function find_coldest_out_loop will return a loop NOT accord with our
>> expectation, that should return second_coldest_loop instead of
>> outermost_loop?
> Hmm, interesting - yes. I guess the common case will be that the pre-computed
> outermost loop will be the loop at depth 1 since outer loops tend to
> be colder than
> inner loops? That would then defeat the whole exercise.
It is not easy to construct such cases, But finally I got below results,
1) many cases inner loop is hotter than outer loop, for example:
loop 1's coldest_outermost_loop is 1, colder_than_inner_loop is NULL
loop 2's coldest_outermost_loop is 1, colder_than_inner_loop is 1
loop 3's coldest_outermost_loop is 1, colder_than_inner_loop is 2
loop 4's coldest_outermost_loop is 1, colder_than_inner_loop is 2
2) But there are also cases inner loop is colder than outer loop, like:
loop 1's coldest outermost loop is 1, colder_than_inner_loop is NULL
loop 2's coldest outermost loop is 2, colder_than_inner_loop is NULL
loop 3's coldest outermost loop is 3, colder_than_inner_loop is NULL
>
> To optimize the common case but not avoiding iteration in the cases we care
> about we could instead cache the next outermost loop that is _not_ colder
> than loop. So for your [ ... ] example above we'd have>
> hotter_than_inner_loop[loop] == outer (second_coldest_loop), where the
> candidate would then be 'second_coldest_loop' and we'd then iterate
> to hotter_than_inner_loop[hotter_than_inner_loop[loop]] to find the next
> cold candidate we can compare against? For the common case we'd
> have hotter_than_inner_loop[looo] == NULL (no such loop) and we then
> simply pick 'outermost_loop'.
Thanks. It was difficult to understand, but finally I got to know what you
want to express :)
We should cache the next loop that is *colder* than loop instead of '_not_
colder
than loop', and 'hotter_than_inner_loop' should be 'colder_than_inner_loop',
then it makes sense if the coldest loop is outside of outermost loop, continue
to
find a colder loop between outermost loop and current loop in
colder_than_inner_loop[loop->num]? Hope I understood you correctly...
>
> One comment on the patch itself below.
>
The loop in fill_cold_out_loop is also removed in the updated v7 patch.
[PATCH v7 2/2] Don't move cold code out of loop by checking bb count
From: Xiong Hu Luo <luo...@linux.ibm.com>
v7 changes:
1. Refine get_coldest_out_loop to replace loop with checking
pre-computed coldest_outermost_loop and colder_than_inner_loop.
2. Add function fill_cold_out_loop, compute coldest_outermost_loop and
colder_than_inner_loop recursively without loop.
v6 changes:
1. Add function fill_coldest_out_loop to pre compute the coldest
outermost loop for each loop.
2. Rename find_coldest_out_loop to get_coldest_out_loop.
3. Add testcase ssa-lim-22.c to differentiate with ssa-lim-19.c.
v5 changes:
1. Refine comments for new functions.
2. Use basic_block instead of count in bb_colder_than_loop_preheader
to align with function name.
3. Refine with simpler implementation for get_coldest_out_loop and
ref_in_loop_hot_body::operator for better understanding.
v4 changes:
1. Sort out profile_count comparision to function bb_cold_than_loop_preheader.
2. Update ref_in_loop_hot_body::operator () to find cold_loop before compare.
3. Split RTL invariant motion part out.
4. Remove aux changes.
v3 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
v3: https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580211.html
v4: https://gcc.gnu.org/pipermail/gcc-patches/2021-October/581231.html
v5: https://gcc.gnu.org/pipermail/gcc-patches/2021-October/581961.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 get_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:
* tree-ssa-loop-im.c (bb_colder_than_loop_preheader): New
function.
(get_coldest_out_loop): New function.
(determine_max_movement): Use get_coldest_out_loop.
(move_computations_worker): Adjust and fix iteration udpate.
(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.
(fill_cold_out_loop): New.
(tree_ssa_lim_finalize): Free coldest_outermost_loop and
colder_than_inner_loop.
(loop_invariant_motion_in_fun): Call fill_cold_out_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.dg/tree-ssa/ssa-lim-21.c: New test.
* gcc.dg/tree-ssa/ssa-lim-22.c: New test.
---
gcc/tree-ssa-loop-im.c | 140 ++++++++++++++++++++-
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 | 29 +++++
gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-20.c | 25 ++++
gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-21.c | 35 ++++++
gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-22.c | 32 +++++
7 files changed, 280 insertions(+), 3 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
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-22.c
diff --git a/gcc/tree-ssa-loop-im.c b/gcc/tree-ssa-loop-im.c
index 4b187c2cdaf..e9b3d0cba93 100644
--- a/gcc/tree-ssa-loop-im.c
+++ b/gcc/tree-ssa-loop-im.c
@@ -146,6 +146,11 @@ public:
enum dep_kind { lim_raw, sm_war, sm_waw };
enum dep_state { dep_unknown, dep_independent, dep_dependent };
+/* coldest outermost loop for given loop. */
+class loop **coldest_outermost_loop;
+/* colder outer loop nerest to given loop. */
+class loop **colder_than_inner_loop;
+
/* Populate the loop dependence cache of REF for LOOP, KIND with STATE. */
static void
@@ -417,6 +422,53 @@ movement_possibility (gimple *stmt)
return ret;
}
+/* Compare the profile count inequality of bb and preheader, it is three-state
+ as stated in profile-count.h, FALSE is returned if inequality cannot be
+ decided. */
+bool bb_colder_than_loop_preheader (basic_block bb, basic_block preheader)
+{
+ gcc_assert (bb && preheader);
+ return bb->count < preheader->count;
+}
+
+/* Check coldest loop between OUTERMOST_LOOP and LOOP by comparing profile
+ count.
+ It does three steps check:
+ 1) Check whether CURR_BB is cold in it's own loop_father, if it is cold, just
+ return NULL which means it should not be moved out at all;
+ 2) CURR_BB is NOT cold, check if pre-computed COLDEST_LOOP is outside of
+ OUTERMOST_LOOP, if it is inside of OUTERMOST_LOOP, return the COLDEST_LOOP;
+ 3) If COLDEST_LOOP is outside of OUTERMOST_LOOP, check whether there is a
+ colder loop between OUTERMOST_LOOP and loop in pre-computed
+ COLDER_THAN_INNER_LOOP, return it, otherwise return OUTERMOST_LOOP. */
+
+static class loop *
+get_coldest_out_loop (class loop *outermost_loop, class loop *loop,
+ basic_block curr_bb)
+{
+ gcc_assert (outermost_loop == loop
+ || flow_loop_nested_p (outermost_loop, loop));
+
+ /* If bb_colder_than_loop_preheader returns false due to three-state
+ comparision, OUTERMOST_LOOP is returned finally to preserve the behavior.
+ Otherwise, return the coldest loop between OUTERMOST_LOOP and LOOP. */
+ if (curr_bb
+ && bb_colder_than_loop_preheader (curr_bb,
+ loop_preheader_edge (loop)->src))
+ return NULL;
+
+ class loop *coldest_loop = coldest_outermost_loop[loop->num];
+ if (loop_depth (coldest_loop) < loop_depth (outermost_loop))
+ {
+ if (colder_than_inner_loop[loop->num] != NULL
+ && loop_depth (outermost_loop)
+ < loop_depth (colder_than_inner_loop[loop->num]))
+ return colder_than_inner_loop[loop->num];
+ return outermost_loop;
+ }
+ return coldest_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 +737,9 @@ 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 = get_coldest_out_loop (level, loop, bb);
+ if (!lim_data->max_loop)
+ return false;
if (gphi *phi = dyn_cast <gphi *> (stmt))
{
@@ -1221,7 +1275,10 @@ 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))
{
@@ -2887,6 +2944,26 @@ 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;
+};
+
+/* Check the coldest loop between loop L and innermost loop. If there is one
+ cold loop between L and INNER_LOOP, store motion can be performed, otherwise
+ no cold loop means no store motion. get_coldest_out_loop also handles cases
+ when l is inner_loop. */
+bool
+ref_in_loop_hot_body::operator () (mem_ref_loc *loc)
+{
+ basic_block curr_bb = gimple_bb (loc->stmt);
+ class loop *inner_loop = curr_bb->loop_father;
+ return get_coldest_out_loop (l, inner_loop, curr_bb);
+}
+
/* Returns true if we can perform store motion of REF from LOOP. */
@@ -2941,6 +3018,12 @@ can_sm_ref_p (class loop *loop, im_mem_ref *ref)
if (!ref_indep_loop_p (loop, ref, sm_war))
return false;
+ /* Verify whether the candidate is hot for LOOP. Only do store motion if the
+ candidate's profile count is hot. Statement in cold BB shouldn't be moved
+ out of it's loop_father. */
+ if (!for_all_locs_in_loop (loop, ref, ref_in_loop_hot_body (loop)))
+ return false;
+
return true;
}
@@ -3153,6 +3236,48 @@ fill_always_executed_in (void)
fill_always_executed_in_1 (loop, contains_call);
}
+/* Find the coldest loop preheader for LOOP, also find the nearest colder loop
+ to LOOP. Then recursively iterate each inner loop. */
+
+void
+fill_cold_out_loop (class loop *coldest_loop, class loop *outer_loop,
+ class loop *loop)
+{
+ class loop *colder_loop = NULL;
+ if (outer_loop)
+ {
+ if (bb_colder_than_loop_preheader (loop_preheader_edge (outer_loop)->src,
+ loop_preheader_edge (loop)->src))
+ colder_loop = outer_loop;
+ else if (colder_than_inner_loop[outer_loop->num]
+ && bb_colder_than_loop_preheader (
+ loop_preheader_edge (colder_than_inner_loop[outer_loop->num])
+ ->src,
+ loop_preheader_edge (loop)->src))
+ colder_loop = colder_than_inner_loop[outer_loop->num];
+ }
+
+ if (bb_colder_than_loop_preheader (loop_preheader_edge (loop)->src,
+ loop_preheader_edge (coldest_loop)->src))
+ coldest_loop = loop;
+
+ coldest_outermost_loop[loop->num] = coldest_loop;
+ colder_than_inner_loop[loop->num] = colder_loop;
+ if (dump_enabled_p ())
+ {
+ dump_printf (MSG_NOTE, "loop %d's coldest_outermost_loop is %d, ",
+ loop->num, coldest_loop->num);
+ if (colder_loop)
+ dump_printf (MSG_NOTE, "colder_than_inner_loop is %d\n",
+ colder_loop->num);
+ else
+ dump_printf (MSG_NOTE, "colder_than_inner_loop is NULL\n");
+ }
+
+ class loop *inner_loop;
+ for (inner_loop = loop->inner; inner_loop; inner_loop = inner_loop->next)
+ fill_cold_out_loop (coldest_loop, loop, inner_loop);
+}
/* Compute the global information needed by the loop invariant motion pass. */
@@ -3237,6 +3362,9 @@ tree_ssa_lim_finalize (void)
free_affine_expand_cache (&memory_accesses.ttae_cache);
free (bb_loop_postorder);
+
+ free (coldest_outermost_loop);
+ free (colder_than_inner_loop);
}
/* Moves invariants from loops. Only "expensive" invariants are moved out --
@@ -3256,6 +3384,14 @@ loop_invariant_motion_in_fun (function *fun, bool
store_motion)
/* Fills ALWAYS_EXECUTED_IN information for basic blocks. */
fill_always_executed_in ();
+ /* Pre-compute coldest outermost loop and nearest colder loop of each loop.
+ */
+ class loop *loop;
+ coldest_outermost_loop = XNEWVEC (class loop *, number_of_loops (cfun));
+ colder_than_inner_loop = XNEWVEC (class loop *, number_of_loops (cfun));
+ for (loop = current_loops->tree_root->inner; loop != NULL; loop = loop->next)
+ fill_cold_out_loop (loop, NULL, loop);
+
int *rpo = XNEWVEC (int, last_basic_block_for_fn (fun));
int n = pre_and_rev_post_order_compute_fn (fun, NULL, rpo, false);
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..51c1913d003
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-19.c
@@ -0,0 +1,29 @@
+/* { 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 s, int t)
+{
+ int i;
+ int j;
+ int k;
+
+ for (i = 0; i < m; i++) // Loop 1
+ {
+ if (__builtin_expect (x, 0))
+ for (j = 0; j < n; j++) // Loop 2
+ for (k = 0; k < n; k++) // Loop 3
+ {
+ bar (s / 5, "one", "two");
+ a[t] = s;
+ }
+ a[t] = t;
+ }
+}
+
+/* { 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..ffe6f8f699d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-21.c
@@ -0,0 +1,35 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-lim2-details" } */
+
+/* Test that `data' and 'data1' is not hoisted out of inner loop and outer loop
+ when it is in cold loop. */
+
+int count;
+volatile int x;
+
+struct obj {
+ int data;
+ int data1;
+ struct obj *next;
+};
+
+void
+func (int m, int n, int k, struct obj *a)
+{
+ struct obj *q = a;
+ for (int j = 0; j < m; j++)
+ if (__builtin_expect (m, 0))
+ for (int i = 0; i < m; i++)
+ {
+ if (__builtin_expect (x, 0))
+ {
+ count++;
+ q->data += 3; /* Not hoisted out to inner loop. */
+ }
+ count += n;
+ q->data1 += k; /* Not hoisted out to outer loop. */
+ }
+}
+
+/* { dg-final { scan-tree-dump-not "Executing store motion of" "lim2" } } */
+
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-22.c
b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-22.c
new file mode 100644
index 00000000000..16ba4ceb8ab
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-lim-22.c
@@ -0,0 +1,32 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-lim2-details" } */
+
+volatile int x;
+volatile int y;
+void
+bar (int, char *, char *);
+void
+foo (int *a, int n, int m, int s, int t)
+{
+ int i;
+ int j;
+ int k;
+
+ for (i = 0; i < m; i++) // Loop 1
+ {
+ if (__builtin_expect (x, 0))
+ for (j = 0; j < n; j++) // Loop 2
+ if (__builtin_expect (y, 0))
+ for (k = 0; k < n; k++) // Loop 3
+ {
+ bar (s / 5, "one", "two");
+ a[t] = s;
+ }
+ a[t] = t;
+ }
+}
+
+/* { dg-final { scan-tree-dump-times "out of loop 3" 4 "lim2" } } */
+/* { dg-final { scan-tree-dump-times "out of loop 1" 3 "lim2" } } */
+
+
--
2.27.0.90.geebb51ba8c
