Update the patch since v2:
. Check index and bound from gcond before checking if wrap.
. Update test case, and add an executable case.
. Refine code comments.
. Enhance the checking for i++/++i in the loop header.
. Enhance code to handle equal condition on exit
Bootstrap and regtest pass on powerpc64le, and also pass regtest
on bootstrap-O3. Is this ok for trunk?
BR.
Jiufu Guo.
When there is the possibility that wrap may happen on the loop index,
a few optimizations would not happen. For example code:
foo (int *a, int *b, unsigned k, unsigned n)
{
while (++k != n)
a[k] = b[k] + 1;
}
For this code, if "k > n", k would wrap. if "k < n" at begining,
it could be optimized (e.g. vectorization).
We can split the loop into two loops:
while (++k > n)
a[k] = b[k] + 1;
while (k++ < n)
a[k] = b[k] + 1;
This patch splits this kind of loop to achieve better performance.
gcc/ChangeLog:
2021-06-04 Jiufu Guo <guoji...@linux.ibm.com>
* tree-ssa-loop-split.c (connect_loop_phis): Add new param.
(get_ne_cond_branch): New function.
(split_ne_loop): New function.
(split_loop_on_ne_cond): New function.
(tree_ssa_split_loops): Use split_loop_on_ne_cond.
gcc/testsuite/ChangeLog:
2021-06-04 Jiufu Guo <guoji...@linux.ibm.com>
* gcc.dg/loop-split1.c: New test.
* gcc.dg/loop-split2.c: New test.
* g++.dg/vect/pr98064.cc: Suppress warning.
---
gcc/testsuite/g++.dg/vect/pr98064.cc | 4 +-
gcc/testsuite/gcc.dg/loop-split1.c | 101 +++++++++++
gcc/testsuite/gcc.dg/loop-split2.c | 54 ++++++
gcc/tree-ssa-loop-split.c | 251 ++++++++++++++++++++++++++-
4 files changed, 404 insertions(+), 6 deletions(-)
create mode 100644 gcc/testsuite/gcc.dg/loop-split1.c
create mode 100644 gcc/testsuite/gcc.dg/loop-split2.c
diff --git a/gcc/testsuite/g++.dg/vect/pr98064.cc
b/gcc/testsuite/g++.dg/vect/pr98064.cc
index 74043ce7725..dcb2985d05a 100644
--- a/gcc/testsuite/g++.dg/vect/pr98064.cc
+++ b/gcc/testsuite/g++.dg/vect/pr98064.cc
@@ -1,5 +1,7 @@
// { dg-do compile }
-// { dg-additional-options "-O3" }
+// { dg-additional-options "-O3 -Wno-stringop-overflow" }
+/* There is warning message when "short g = var_8; g; g++"
+ is optimized/analyzed as string operation,e.g. memset. */
const long long &min(const long long &__a, long long &__b) {
if (__b < __a)
diff --git a/gcc/testsuite/gcc.dg/loop-split1.c
b/gcc/testsuite/gcc.dg/loop-split1.c
new file mode 100644
index 00000000000..dd2d03a7b96
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/loop-split1.c
@@ -0,0 +1,101 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fsplit-loops -fdump-tree-lsplit-details" } */
+
+void
+foo (int *a, int *b, unsigned l, unsigned n)
+{
+ while (++l != n)
+ a[l] = b[l] + 1;
+}
+void
+foo_1 (int *a, int *b, unsigned n)
+{
+ unsigned l = 0;
+ while (++l != n)
+ a[l] = b[l] + 1;
+}
+
+void
+foo1 (int *a, int *b, unsigned l, unsigned n)
+{
+ while (l++ != n)
+ a[l] = b[l] + 1;
+}
+
+/* No wrap. */
+void
+foo1_1 (int *a, int *b, unsigned n)
+{
+ unsigned l = 0;
+ while (l++ != n)
+ a[l] = b[l] + 1;
+}
+
+unsigned
+foo2 (char *a, char *b, unsigned l, unsigned n)
+{
+ while (++l != n)
+ if (a[l] != b[l])
+ break;
+
+ return l;
+}
+
+unsigned
+foo2_1 (char *a, char *b, unsigned l, unsigned n)
+{
+ l = 0;
+ while (++l != n)
+ if (a[l] != b[l])
+ break;
+
+ return l;
+}
+
+unsigned
+foo3 (char *a, char *b, unsigned l, unsigned n)
+{
+ while (l++ != n)
+ if (a[l] != b[l])
+ break;
+
+ return l;
+}
+
+/* No wrap. */
+unsigned
+foo3_1 (char *a, char *b, unsigned l, unsigned n)
+{
+ l = 0;
+ while (l++ != n)
+ if (a[l] != b[l])
+ break;
+
+ return l;
+}
+
+void
+bar ();
+void
+foo4 (unsigned n, unsigned i)
+{
+ do
+ {
+ if (i == n)
+ return;
+ bar ();
+ ++i;
+ }
+ while (1);
+}
+
+unsigned
+find_skip_diff (char *p, char *q, unsigned n, unsigned i)
+{
+ while (p[i] == q[i] && ++i != n)
+ p++, q++;
+
+ return i;
+}
+
+/* { dg-final { scan-tree-dump-times "Loop split" 8 "lsplit" } } */
diff --git a/gcc/testsuite/gcc.dg/loop-split2.c
b/gcc/testsuite/gcc.dg/loop-split2.c
new file mode 100644
index 00000000000..0d3fded3f61
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/loop-split2.c
@@ -0,0 +1,54 @@
+/* { dg-do run } */
+/* { dg-options "-O3" } */
+
+extern void abort (void);
+extern void exit (int);
+
+#define NI __attribute__ ((noinline))
+
+void NI
+foo (int *a, int *b, unsigned char l, unsigned char n)
+{
+ while (++l != n)
+ a[l] = b[l] + 1;
+}
+
+unsigned NI
+bar (int *a, int *b, unsigned char l, unsigned char n)
+{
+ while (l++ != n)
+ if (a[l] != b[l])
+ break;
+
+ return l;
+}
+
+int a[258];
+int b[258];
+
+int main()
+{
+ __builtin_memcpy (b, a, sizeof (a));
+
+ if (bar (a, b, 3, 8) != 9)
+ abort ();
+
+ if (bar (a, b, 8, 3) != 4)
+ abort ();
+
+ b[100] += 1;
+ if (bar (a, b, 90, 110) != 100)
+ abort ();
+
+ if (bar (a, b, 110, 105) != 100)
+ abort ();
+
+ foo (a, b, 99, 99);
+ a[99] = b[99] + 1;
+ for (int i = 0; i < 256; i++)
+ if (a[i] != b[i] + 1)
+ abort();
+
+ exit (0);
+}
+
diff --git a/gcc/tree-ssa-loop-split.c b/gcc/tree-ssa-loop-split.c
index 3a09bbc39e5..9c0de66e288 100644
--- a/gcc/tree-ssa-loop-split.c
+++ b/gcc/tree-ssa-loop-split.c
@@ -41,6 +41,7 @@ along with GCC; see the file COPYING3. If not see
#include "cfghooks.h"
#include "gimple-fold.h"
#include "gimplify-me.h"
+#include "tree-ssa-loop-ivopts.h"
/* This file implements two kinds of loop splitting.
@@ -229,11 +230,14 @@ easy_exit_values (class loop *loop)
conditional). I.e. the second loop can now be entered either
via the original entry or via NEW_E, so the entry values of LOOP2
phi nodes are either the original ones or those at the exit
- of LOOP1. Insert new phi nodes in LOOP2 pre-header reflecting
- this. The loops need to fulfill easy_exit_values(). */
+ of LOOP1. Selecting the previous value instead next value as the
+ exit value of LOOP1 if USE_PREV is true. Insert new phi nodes in
+ LOOP2 pre-header reflecting this. The loops need to fulfill
+ easy_exit_values(). */
static void
-connect_loop_phis (class loop *loop1, class loop *loop2, edge new_e)
+connect_loop_phis (class loop *loop1, class loop *loop2, edge new_e,
+ bool use_prev = false)
{
basic_block rest = loop_preheader_edge (loop2)->src;
gcc_assert (new_e->dest == rest);
@@ -279,7 +283,8 @@ connect_loop_phis (class loop *loop1, class loop *loop2,
edge new_e)
gphi * newphi = create_phi_node (new_init, rest);
add_phi_arg (newphi, init, skip_first, UNKNOWN_LOCATION);
- add_phi_arg (newphi, next, new_e, UNKNOWN_LOCATION);
+ add_phi_arg (newphi, use_prev ? PHI_RESULT (phi_first) : next, new_e,
+ UNKNOWN_LOCATION);
SET_USE (op, new_init);
}
}
@@ -1593,6 +1598,241 @@ split_loop_on_cond (struct loop *loop)
return do_split;
}
+/* Check if the LOOP exit branch is like "if (idx != bound)",
+ Return the branch edge which exit loop, if wrap may happen on "idx". */
+
+static edge
+get_ne_cond_branch (struct loop *loop)
+{
+ int i;
+ edge e;
+
+ auto_vec<edge> edges = get_loop_exit_edges (loop);
+ FOR_EACH_VEC_ELT (edges, i, e)
+ {
+ basic_block bb = e->src;
+
+ /* Check if exit at gcond. */
+ gimple *last = last_stmt (bb);
+ if (!last || gimple_code (last) != GIMPLE_COND)
+ continue;
+ gcond *cond = as_a<gcond *> (last);
+ enum tree_code code = gimple_cond_code (cond);
+ if (!(code == NE_EXPR
+ || (code == EQ_EXPR && (e->flags & EDGE_TRUE_VALUE))))
+ continue;
+
+ /* Check if bound is invarant. */
+ tree idx = gimple_cond_lhs (cond);
+ tree bnd = gimple_cond_rhs (cond);
+ if (expr_invariant_in_loop_p (loop, idx))
+ std::swap (idx, bnd);
+ else if (!expr_invariant_in_loop_p (loop, bnd))
+ continue;
+
+ /* Only unsigned type conversion could cause wrap. */
+ tree type = TREE_TYPE (idx);
+ if (!INTEGRAL_TYPE_P (type) || TREE_CODE (idx) != SSA_NAME
+ || !TYPE_UNSIGNED (type))
+ continue;
+
+ /* Avoid to split if bound is MAX/MIN val. */
+ tree bound_type = TREE_TYPE (bnd);
+ if (TREE_CODE (bnd) == INTEGER_CST && INTEGRAL_TYPE_P (bound_type)
+ && (tree_int_cst_equal (bnd, TYPE_MAX_VALUE (bound_type))
+ || tree_int_cst_equal (bnd, TYPE_MIN_VALUE (bound_type))))
+ continue;
+
+ /* Check if there is possible wrap. */
+ class tree_niter_desc niter;
+ if (!number_of_iterations_exit (loop, e, &niter, false, false))
+ continue;
+ if (niter.control.no_overflow)
+ return NULL;
+ if (niter.cmp != NE_EXPR)
+ continue;
+
+ /* If exit edge is just before the empty latch, it is easy to link
+ the split loops: just jump from the exit edge of one loop to the
+ header of new loop. */
+ if (single_pred_p (loop->latch)
+ && single_pred_edge (loop->latch)->src == bb
+ && empty_block_p (loop->latch))
+ return e;
+
+ /* If exit edge is at end of header, and header contains i++ or ++i,
+ only, it is simple to link the split loops: jump from the end of
+ one loop header to the new loop header, and use unchanged PHI
+ result of first loop as the entry PHI value of the second loop. */
+ if (bb == loop->header)
+ {
+ /* Only one phi. */
+ gphi_iterator psi = gsi_start_phis (bb);
+ if (gsi_end_p (psi))
+ continue;
+ gphi *phi = psi.phi ();
+ gsi_next (&psi);
+ if (!gsi_end_p (psi))
+ continue;
+
+ /* Check it is ++i or ++i */
+ tree next = PHI_ARG_DEF_FROM_EDGE (phi, loop_latch_edge (loop));
+ tree prev = PHI_RESULT (phi);
+ if (idx != prev && idx != next)
+ continue;
+
+ gimple_stmt_iterator gsi = gsi_start_nondebug_after_labels_bb (bb);
+ if (gsi_end_p (gsi))
+ continue;
+ gimple *s1 = gsi_stmt (gsi);
+ if (!is_gimple_assign (s1) || gimple_assign_lhs (s1) != next
+ || gimple_assign_rhs1 (s1) != prev)
+ continue;
+
+ gsi_next_nondebug (&gsi);
+ if (!gsi_end_p (gsi) && gsi_stmt (gsi) == cond)
+ return e;
+ }
+ }
+
+ return NULL;
+}
+
+/* Split the LOOP with NE_EXPR into two loops with GT_EXPR and LT_EXPR. */
+
+static bool
+split_ne_loop (struct loop *loop, edge cond_e)
+{
+ initialize_original_copy_tables ();
+
+ struct loop *loop2 = loop_version (loop, boolean_true_node, NULL,
+ profile_probability::always (),
+ profile_probability::never (),
+ profile_probability::always (),
+ profile_probability::always (), true);
+
+ gcc_assert (loop2);
+ update_ssa (TODO_update_ssa);
+
+ basic_block loop2_cond_exit_bb = get_bb_copy (cond_e->src);
+ free_original_copy_tables ();
+
+ gcond *gc = as_a<gcond *> (last_stmt (cond_e->src));
+ gcond *dup_gc = as_a<gcond *> (last_stmt (loop2_cond_exit_bb));
+
+ /* Invert edges for gcond. */
+ if (gimple_cond_code (gc) == EQ_EXPR)
+ {
+ auto invert_edge = [](basic_block bb) {
+ edge out = EDGE_SUCC (bb, 0);
+ edge in = EDGE_SUCC (bb, 1);
+ if (in->flags & EDGE_TRUE_VALUE)
+ std::swap (in, out);
+ in->flags |= EDGE_TRUE_VALUE;
+ in->flags &= ~EDGE_FALSE_VALUE;
+ out->flags |= EDGE_FALSE_VALUE;
+ out->flags &= ~EDGE_TRUE_VALUE;
+ };
+
+ invert_edge (gimple_bb (gc));
+ invert_edge (gimple_bb (dup_gc));
+ }
+
+ /* Change if (i != n) to LOOP1:if (i > n) and LOOP2:if (i < n) */
+ bool inv = expr_invariant_in_loop_p (loop, gimple_cond_lhs (gc));
+ enum tree_code up_code = inv ? LT_EXPR : GT_EXPR;
+ enum tree_code down_code = inv ? GT_EXPR : LT_EXPR;
+
+ gimple_cond_set_code (gc, up_code);
+ gimple_cond_set_code (dup_gc, down_code);
+
+ /* Link the exit cond edge to new loop. */
+ gcond *break_cond = as_a<gcond *> (gimple_copy (gc));
+ edge pred_e = single_pred_edge (loop->latch);
+ bool simple_loop
+ = pred_e && pred_e->src == cond_e->src && empty_block_p (loop->latch);
+ if (simple_loop)
+ gimple_cond_set_code (break_cond, down_code);
+ else
+ gimple_cond_make_true (break_cond);
+
+ basic_block break_bb = split_edge (cond_e);
+ gimple_stmt_iterator gsi = gsi_last_bb (break_bb);
+ gsi_insert_after (&gsi, break_cond, GSI_NEW_STMT);
+
+ edge to_exit = single_succ_edge (break_bb);
+ edge to_new_loop = make_edge (break_bb, loop_preheader_edge (loop2)->src, 0);
+ to_new_loop->flags |= EDGE_TRUE_VALUE;
+ to_exit->flags |= EDGE_FALSE_VALUE;
+ to_exit->flags &= ~EDGE_FALLTHRU;
+ to_exit->probability = cond_e->probability;
+ to_new_loop->probability = to_exit->probability.invert ();
+
+ update_ssa (TODO_update_ssa);
+
+ connect_loop_phis (loop, loop2, to_new_loop, !simple_loop);
+
+ rewrite_into_loop_closed_ssa_1 (NULL, 0, SSA_OP_USE, loop);
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ fprintf (dump_file, ";; Loop split on wrap index.\n");
+
+ return true;
+}
+
+/* Checks if LOOP contains a suitable NE_EXPR conditional block to split.
+L_H:
+ if (i!=N)
+ S;
+ else
+ goto EXIT;
+ i++;
+ goto L_H;
+
+The "i!=N" is like "i>N || i<N", then it could be transform to:
+
+L_H:
+ if (i>N)
+ S;
+ else
+ goto EXIT;
+ i++;
+ goto L_H;
+L1_H:
+ if (i<N)
+ S;
+ else
+ goto EXIT;
+ i++;
+ goto L1_H;
+
+The loop with "i<N" is in favor both GIMPLE and RTL passes. */
+
+static bool
+split_loop_on_ne_cond (class loop *loop)
+{
+ int num = 0;
+ basic_block *bbs = get_loop_body (loop);
+
+ if (!can_copy_bbs_p (bbs, loop->num_nodes))
+ {
+ free (bbs);
+ return false;
+ }
+
+ for (unsigned i = 0; i < loop->num_nodes; i++)
+ num += estimate_num_insns_seq (bb_seq (bbs[i]), &eni_size_weights);
+ free (bbs);
+
+ if (num > param_max_peeled_insns)
+ return false;
+
+ edge branch_edge = get_ne_cond_branch (loop);
+ if (branch_edge && split_ne_loop (loop, branch_edge))
+ return true;
+
+ return false;
+}
+
/* Main entry point. Perform loop splitting on all suitable loops. */
static unsigned int
@@ -1622,7 +1862,8 @@ tree_ssa_split_loops (void)
if (optimize_loop_for_size_p (loop))
continue;
- if (split_loop (loop) || split_loop_on_cond (loop))
+ if (split_loop (loop) || split_loop_on_cond (loop)
+ || split_loop_on_ne_cond (loop))
{
/* Mark our containing loop as having had some split inner loops. */
loop_outer (loop)->aux = loop;
--
2.17.1
