[ was: Re: [PING][PATCH][PR65443] Add transform_to_exit_first_loop_alt ]
On 14/05/15 13:42, Tom de Vries wrote:
On 20-04-15 14:25, Richard Biener wrote:
On Wed, 15 Apr 2015, Tom de Vries wrote:
On 03-04-15 14:39, Tom de Vries wrote:
On 27-03-15 15:10, Tom de Vries wrote:
Hi,
this patch fixes PR65443, a todo in the parloops pass for function
transform_to_exit_first_loop:
...
TODO: the common case is that latch of the loop is empty and
immediately
follows the loop exit. In this case, it would be better not
to copy
the
body of the loop, but only move the entry of the loop directly
before
the
exit check and increase the number of iterations of the loop
by one.
This may need some additional preconditioning in case NIT = ~0.
...
The current implementation of transform_to_exit_first_loop
transforms the
loop
by moving and duplicating the loop body. This patch transforms the
loop
into the
same normal form, but without the duplication, if that's possible
(determined by
try_transform_to_exit_first_loop_alt).
The actual transformation, done by transform_to_exit_first_loop_alt
transforms
this loop:
...
bb preheader:
...
goto <bb header>
<bb header>:
...
if (ivtmp < n)
goto <bb latch>;
else
goto <bb exit>;
<bb latch>:
ivtmp = ivtmp + inc;
goto <bb header>
...
into this one:
...
bb preheader:
...
goto <bb newheader>
<bb header>:
...
goto <bb latch>;
<bb newheader>:
if (ivtmp < n + 1)
goto <bb header>;
else
goto <bb exit>;
<bb latch>:
ivtmp = ivtmp + inc;
goto <bb newheader>
...
Updated patch, now using redirect_edge_var_map and flush_pending_stmts.
Bootstrapped and reg-tested on x86_64.
OK for stage1 trunk?
Ping.
Hi Richard,
thanks for the review.
+static void
+replace_imm_uses (tree val, imm_use_iterator *imm_iter)
+{
+ use_operand_p use_p;
+
+ FOR_EACH_IMM_USE_ON_STMT (use_p, *imm_iter)
+ SET_USE (use_p, val);
Use propagate_value. Why this odd interface passing a imm_iter?!
The replace_imm_uses function is common code factored out of
replace_uses_in_bb_by and replace_uses_in_bbs_by. I'm not sure what is
odd about the interface of the replace_imm_uses function, but I've
removed the function.
I tried using propagate_value, but that one doesn't like virtuals.
In fact most of the "repair SSA" in transform_to_exit_first_loop_alt
looks too ad-hoc to me ... it also looks somewhat familiar to other
code ...
Unfortunately the comment before the function isn't in SSA form
so it's hard to follow the transform.
I've added the ssa bits in the transformation comment before the
function, and updated variable names and comments in the function.
I consider the parloops code bitrotten, no repair possible, so
I might be convinced to not care about new spaghetti in there...
+ /* Fix up loop structure. TODO: Check whether this is sufficient. */
+ loop->header = new_header;
+
no, surely not. Number of iterations (and estimates) are off
after the transform
The loop is cancelled at the end of gen_parallel_loop, and the
estimations are removed. We only seem to be using a limited set of the
loop data until the loop is cancelled. Updated comment accordingly.
and loop->latch might also need updating.
That one actually stays the same. Updated comment accordingly.
"Safest" is to simply schedule a fixup (but you'll lose any
loop annotation in that process).
Since the loop is cancelled, AFAIU we don't need that, but... You're
referring to the annotations mentioned in
replace_loop_annotate_in_block? Losing the annotations seems to be a
generic problem of scheduling such a fixup, not particular to this
patch. Do you have a concern related to the patch and these annotations?
+ /* Figure out whether nit + 1 overflows. */
+ if (TREE_CODE (nit) == INTEGER_CST)
+ {
+ if (!tree_int_cst_equal (nit, TYPE_MAXVAL (nit_type)))
in case nit_type is a pointer type TYPE_MAXVAL will be NULL I think.
We've done ivcanon just before this point, so AFAIU we can assume we're
dealing with an unsigned integer.
Is the whole exercise for performance?
I'm trying to fix the todo in the code for parloops, which is about
performance, though I don't expect a large gain.
OTOH, my main focus is a related oacc kernels issue. For an oacc kernels
region, the entire loop is enclosed in a kernels region. Peeling of the
last iteration means I have to guard that iteration to run on only one
thread, which currently isn't done, so in that sense it's a correctness
issue as well.
In that case using an
entirely new, unsigned IV, that runs from 0 to niter should be easiest
and
Introducting such an IV would mean that we don't have to update the IV,
but still we have to connect the new IV to the uses of the old IV.
The current special handling of the IV variable is actually not that
elaborate:
...
+ /* Replace ivtmp_a with ivtmp_c in condition 'if (ivtmp_a < n)'. */
+ replace_uses_in_bb_by (res_a, res_c, new_header);
...
So I'm not sure it's easier.
just run-time guard that niter == +INF case?
That doesn't work out nicely for the oacc kernels case. I need to know
compile-time wheter I can parallelize or not.
For the graphite case, can't you make graphite generate the
loops exit-first in the first place?
Perhaps, but that doesn't make a difference for the oacc kernels case.
The testcases are just correctness ones? That is, there isn't
any testcase that checks whether the new code is exercised?
(no extra debugging dumping?)
There are 3 new test patterns, each with a libgomp/testsuite/libgomp.c
and a gcc/testsuite/gcc.dg variant, so 6 new test-cases in total. The
gcc/testsuite/gcc.dg variant checks that the new code is exercised. The
libgomp/testsuite/libgomp.c variant checks that the new code generates
correct code.
Committed to gomp-4_0-branch.
Thanks,
- Tom
Add transform_to_exit_first_loop_alt
2015-05-28 Tom de Vries <t...@codesourcery.com>
PR tree-optimization/65443
* tree-parloops.c (replace_imm_uses, replace_uses_in_bb_by)
(replace_uses_in_bbs_by, transform_to_exit_first_loop_alt)
(try_transform_to_exit_first_loop_alt): New function.
(transform_to_exit_first_loop): Use
try_transform_to_exit_first_loop_alt.
* gcc.dg/parloops-exit-first-loop-alt-2.c: New test.
* gcc.dg/parloops-exit-first-loop-alt-3.c: New test.
* gcc.dg/parloops-exit-first-loop-alt.c: New test.
* testsuite/libgomp.c/parloops-exit-first-loop-alt-2.c: New test.
* testsuite/libgomp.c/parloops-exit-first-loop-alt-3.c: New test.
* testsuite/libgomp.c/parloops-exit-first-loop-alt.c: New test.
diff --git a/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-2.c b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-2.c
new file mode 100644
index 0000000..a4d6cb2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-2.c
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target pthread } */
+/* { dg-options "-O2 -ftree-parallelize-loops=2 -fdump-tree-parloops" } */
+
+#define N 1000
+
+unsigned int a[N];
+unsigned int b[N];
+unsigned int c[N];
+
+void __attribute__((noclone,noinline))
+f (unsigned int n)
+{
+ int i;
+
+ for (i = 0; i < N; ++i)
+ c[i] = a[i] + b[i];
+}
+
+/* Three times three array accesses:
+ - three in f._loopfn.0
+ - three in the parallel
+ - three in the low iteration count loop
+ Crucially, none for a peeled off last iteration following the parallel. */
+/* { dg-final { scan-tree-dump-times "(?n)\\\[i" 9 "parloops" } } */
+
+/* { dg-final { cleanup-tree-dump "parloops" } } */
diff --git a/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-3.c b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-3.c
new file mode 100644
index 0000000..c7ab51f88
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt-3.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target pthread } */
+/* { dg-options "-O2 -ftree-parallelize-loops=2 -fdump-tree-parloops" } */
+
+unsigned int *a;
+
+unsigned int __attribute__((noclone,noinline))
+f (unsigned int n)
+{
+ int i;
+ unsigned int sum = 1;
+
+ for (i = 0; i < n; ++i)
+ sum += a[i];
+
+ return sum;
+}
+
+/* Three array accesses:
+ - one in f._loopfn.0
+ - one in the parallel
+ - one in the low iteration count loop
+ Crucially, none for a peeled off last iteration following the parallel. */
+/* { dg-final { scan-tree-dump-times "(?n)\\\* 4" 3 "parloops" } } */
+
+/* { dg-final { cleanup-tree-dump "parloops" } } */
diff --git a/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt.c b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt.c
new file mode 100644
index 0000000..42ca3ac
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/parloops-exit-first-loop-alt.c
@@ -0,0 +1,27 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target pthread } */
+/* { dg-options "-O2 -ftree-parallelize-loops=2 -fdump-tree-parloops" } */
+
+#define N 1000
+
+unsigned int a[N];
+unsigned int b[N];
+unsigned int c[N];
+
+void __attribute__((noclone,noinline))
+f (unsigned int n)
+{
+ int i;
+
+ for (i = 0; i < n; ++i)
+ c[i] = a[i] + b[i];
+}
+
+/* Three times three array accesses:
+ - three in f._loopfn.0
+ - three in the parallel
+ - three in the low iteration count loop
+ Crucially, none for a peeled off last iteration following the parallel. */
+/* { dg-final { scan-tree-dump-times "(?n)\\\[i" 9 "parloops" } } */
+
+/* { dg-final { cleanup-tree-dump "parloops" } } */
diff --git a/gcc/tree-parloops.c b/gcc/tree-parloops.c
index e10179d..f698eea 100644
--- a/gcc/tree-parloops.c
+++ b/gcc/tree-parloops.c
@@ -78,6 +78,7 @@ along with GCC; see the file COPYING3. If not see
#include "plugin-api.h"
#include "ipa-ref.h"
#include "cgraph.h"
+#include "tree-ssa.h"
/* This pass tries to distribute iterations of loops into several threads.
The implementation is straightforward -- for each loop we test whether its
@@ -1487,17 +1488,386 @@ create_loop_fn (location_t loc)
return decl;
}
-/* Moves the exit condition of LOOP to the beginning of its header, and
- duplicates the part of the last iteration that gets disabled to the
- exit of the loop. NIT is the number of iterations of the loop
- (used to initialize the variables in the duplicated part).
+/* Replace uses of NAME by VAL in block BB. */
- TODO: the common case is that latch of the loop is empty and immediately
- follows the loop exit. In this case, it would be better not to copy the
- body of the loop, but only move the entry of the loop directly before the
- exit check and increase the number of iterations of the loop by one.
- This may need some additional preconditioning in case NIT = ~0.
- REDUCTION_LIST describes the reductions in LOOP. */
+static void
+replace_uses_in_bb_by (tree name, tree val, basic_block bb)
+{
+ gimple use_stmt;
+ imm_use_iterator imm_iter;
+
+ FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, name)
+ {
+ if (gimple_bb (use_stmt) != bb)
+ continue;
+
+ use_operand_p use_p;
+ FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
+ SET_USE (use_p, val);
+ }
+}
+
+/* Replace uses of NAME by VAL in blocks BBS. */
+
+static void
+replace_uses_in_bbs_by (tree name, tree val, bitmap bbs)
+{
+ gimple use_stmt;
+ imm_use_iterator imm_iter;
+
+ FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, name)
+ {
+ if (!bitmap_bit_p (bbs, gimple_bb (use_stmt)->index))
+ continue;
+
+ use_operand_p use_p;
+ FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
+ SET_USE (use_p, val);
+ }
+}
+
+/* Do transformation from:
+
+ <bb preheader>:
+ ...
+ goto <bb header>
+
+ <bb header>:
+ ivtmp_a = PHI <ivtmp_init (preheader), ivtmp_b (latch)>
+ sum_a = PHI <sum_init (preheader), sum_b (latch)>
+ ...
+ use (ivtmp_a)
+ ...
+ sum_b = sum_a + sum_update
+ ...
+ if (ivtmp_a < n)
+ goto <bb latch>;
+ else
+ goto <bb exit>;
+
+ <bb latch>:
+ ivtmp_b = ivtmp_a + 1;
+ goto <bb header>
+
+ <bb exit>:
+ sum_z = PHI <sum_b (cond[1])>
+
+ [1] Where <bb cond> is single_pred (bb latch); In the simplest case,
+ that's <bb header>.
+
+ to:
+
+ <bb preheader>:
+ ...
+ goto <bb newheader>
+
+ <bb header>:
+ ivtmp_a = PHI <ivtmp_c (latch)>
+ sum_a = PHI <sum_c (latch)>
+ ...
+ use (ivtmp_a)
+ ...
+ sum_b = sum_a + sum_update
+ ...
+ goto <bb latch>;
+
+ <bb newheader>:
+ ivtmp_c = PHI <ivtmp_init (preheader), ivtmp_b (latch)>
+ sum_c = PHI <sum_init (preheader), sum_b (latch)>
+ if (ivtmp_c < n + 1)
+ goto <bb header>;
+ else
+ goto <bb exit>;
+
+ <bb latch>:
+ ivtmp_b = ivtmp_a + 1;
+ goto <bb newheader>
+
+ <bb exit>:
+ sum_z = PHI <sum_c (newheader)>
+
+
+ In unified diff format:
+
+ <bb preheader>:
+ ...
+- goto <bb header>
++ goto <bb newheader>
+
+ <bb header>:
+- ivtmp_a = PHI <ivtmp_init (preheader), ivtmp_b (latch)>
+- sum_a = PHI <sum_init (preheader), sum_b (latch)>
++ ivtmp_a = PHI <ivtmp_c (latch)>
++ sum_a = PHI <sum_c (latch)>
+ ...
+ use (ivtmp_a)
+ ...
+ sum_b = sum_a + sum_update
+ ...
+- if (ivtmp_a < n)
+- goto <bb latch>;
++ goto <bb latch>;
++
++ <bb newheader>:
++ ivtmp_c = PHI <ivtmp_init (preheader), ivtmp_b (latch)>
++ sum_c = PHI <sum_init (preheader), sum_b (latch)>
++ if (ivtmp_c < n + 1)
++ goto <bb header>;
+ else
+ goto <bb exit>;
+
+ <bb latch>:
+ ivtmp_b = ivtmp_a + 1;
+- goto <bb header>
++ goto <bb newheader>
+
+ <bb exit>:
+- sum_z = PHI <sum_b (cond[1])>
++ sum_z = PHI <sum_c (newheader)>
+
+ Note: the example does not show any virtual phis, but these are handled more
+ or less as reductions.
+
+
+ Moves the exit condition of LOOP to the beginning of its header.
+ REDUCTION_LIST describes the reductions in LOOP. BOUND is the new loop
+ bound. */
+
+static void
+transform_to_exit_first_loop_alt (struct loop *loop,
+ reduction_info_table_type *reduction_list,
+ tree bound)
+{
+ basic_block header = loop->header;
+ basic_block latch = loop->latch;
+ edge exit = single_dom_exit (loop);
+ basic_block exit_block = exit->dest;
+ gcond *cond_stmt = as_a <gcond *> (last_stmt (exit->src));
+ tree control = gimple_cond_lhs (cond_stmt);
+ edge e;
+
+ /* Gather the bbs dominated by the exit block. */
+ bitmap exit_dominated = BITMAP_ALLOC (NULL);
+ bitmap_set_bit (exit_dominated, exit_block->index);
+ vec<basic_block> exit_dominated_vec
+ = get_dominated_by (CDI_DOMINATORS, exit_block);
+
+ int i;
+ basic_block dom_bb;
+ FOR_EACH_VEC_ELT (exit_dominated_vec, i, dom_bb)
+ bitmap_set_bit (exit_dominated, dom_bb->index);
+
+ exit_dominated_vec.release ();
+
+ /* Create the new_header block. */
+ basic_block new_header = split_block_before_cond_jump (exit->src);
+ edge split_edge = single_pred_edge (new_header);
+
+ /* Redirect entry edge to new_header. */
+ edge entry = loop_preheader_edge (loop);
+ e = redirect_edge_and_branch (entry, new_header);
+ gcc_assert (e == entry);
+
+ /* Redirect post_inc_edge to new_header. */
+ edge post_inc_edge = single_succ_edge (latch);
+ e = redirect_edge_and_branch (post_inc_edge, new_header);
+ gcc_assert (e == post_inc_edge);
+
+ /* Redirect post_cond_edge to header. */
+ edge post_cond_edge = single_pred_edge (latch);
+ e = redirect_edge_and_branch (post_cond_edge, header);
+ gcc_assert (e == post_cond_edge);
+
+ /* Redirect split_edge to latch. */
+ e = redirect_edge_and_branch (split_edge, latch);
+ gcc_assert (e == split_edge);
+
+ /* Set the new loop bound. */
+ gimple_cond_set_rhs (cond_stmt, bound);
+
+ /* Repair the ssa. */
+ vec<edge_var_map> *v = redirect_edge_var_map_vector (post_inc_edge);
+ edge_var_map *vm;
+ gphi_iterator gsi;
+ for (gsi = gsi_start_phis (header), i = 0;
+ !gsi_end_p (gsi) && v->iterate (i, &vm);
+ gsi_next (&gsi), i++)
+ {
+ gphi *phi = gsi.phi ();
+ tree res_a = PHI_RESULT (phi);
+
+ /* Create new phi. */
+ tree res_c = copy_ssa_name (res_a, phi);
+ gphi *nphi = create_phi_node (res_c, new_header);
+
+ /* Replace ivtmp_a with ivtmp_c in condition 'if (ivtmp_a < n)'. */
+ replace_uses_in_bb_by (res_a, res_c, new_header);
+
+ /* Replace ivtmp/sum_b with ivtmp/sum_c in header phi. */
+ add_phi_arg (phi, res_c, post_cond_edge, UNKNOWN_LOCATION);
+
+ /* Replace sum_b with sum_c in exit phi. Loop-closed ssa does not hold
+ for virtuals, so we cannot get away with exit_block only. */
+ tree res_b = redirect_edge_var_map_def (vm);
+ replace_uses_in_bbs_by (res_b, res_c, exit_dominated);
+
+ struct reduction_info *red = reduction_phi (reduction_list, phi);
+ gcc_assert (virtual_operand_p (res_a)
+ || res_a == control
+ || red != NULL);
+
+ if (red)
+ {
+ /* Register the new reduction phi. */
+ red->reduc_phi = nphi;
+ gimple_set_uid (red->reduc_phi, red->reduc_version);
+ }
+ }
+ gcc_assert (gsi_end_p (gsi) && !v->iterate (i, &vm));
+ BITMAP_FREE (exit_dominated);
+
+ /* Set the preheader argument of the new phis to ivtmp/sum_init. */
+ flush_pending_stmts (entry);
+
+ /* Set the latch arguments of the new phis to ivtmp/sum_b. */
+ flush_pending_stmts (post_inc_edge);
+
+ /* Register the reduction exit phis. */
+ for (gphi_iterator gsi = gsi_start_phis (exit_block);
+ !gsi_end_p (gsi);
+ gsi_next (&gsi))
+ {
+ gphi *phi = gsi.phi ();
+ tree res_z = PHI_RESULT (phi);
+ if (virtual_operand_p (res_z))
+ continue;
+
+ tree res_c = PHI_ARG_DEF_FROM_EDGE (phi, exit);
+ gimple reduc_phi = SSA_NAME_DEF_STMT (res_c);
+ struct reduction_info *red = reduction_phi (reduction_list, reduc_phi);
+ if (red != NULL)
+ red->keep_res = phi;
+ }
+
+ /* We're going to cancel the loop at the end of gen_parallel_loop, but until
+ then we're still using some fields, so only bother about fields that are
+ still used: header and latch.
+ The loop has a new header bb, so we update it. The latch bb stays the
+ same. */
+ loop->header = new_header;
+
+ /* Recalculate dominance info. */
+ free_dominance_info (CDI_DOMINATORS);
+ calculate_dominance_info (CDI_DOMINATORS);
+}
+
+/* Tries to moves the exit condition of LOOP to the beginning of its header
+ without duplication of the loop body. NIT is the number of iterations of the
+ loop. REDUCTION_LIST describes the reductions in LOOP. Return true if
+ transformation is successful. */
+
+static bool
+try_transform_to_exit_first_loop_alt (struct loop *loop,
+ reduction_info_table_type *reduction_list,
+ tree nit)
+{
+ /* Check whether the latch contains a single statement. */
+ if (!gimple_seq_singleton_p (bb_seq (loop->latch)))
+ return true;
+
+ /* Check whether the latch contains the loop iv increment. */
+ edge back = single_succ_edge (loop->latch);
+ edge exit = single_dom_exit (loop);
+ gcond *cond_stmt = as_a <gcond *> (last_stmt (exit->src));
+ tree control = gimple_cond_lhs (cond_stmt);
+ gphi *phi = as_a <gphi *> (SSA_NAME_DEF_STMT (control));
+ tree inc_res = gimple_phi_arg_def (phi, back->dest_idx);
+ if (gimple_bb (SSA_NAME_DEF_STMT (inc_res)) != loop->latch)
+ return false;
+
+ /* Check whether there's no code between the loop condition and the latch. */
+ if (!single_pred_p (loop->latch)
+ || single_pred (loop->latch) != exit->src)
+ return false;
+
+ tree alt_bound = NULL_TREE;
+ tree nit_type = TREE_TYPE (nit);
+
+ /* Figure out whether nit + 1 overflows. */
+ if (TREE_CODE (nit) == INTEGER_CST)
+ {
+ if (!tree_int_cst_equal (nit, TYPE_MAXVAL (nit_type)))
+ {
+ alt_bound = fold_build2_loc (UNKNOWN_LOCATION, PLUS_EXPR, nit_type,
+ nit, build_one_cst (nit_type));
+
+ gcc_assert (TREE_CODE (alt_bound) == INTEGER_CST);
+ }
+ else
+ {
+ /* Todo: Figure out if we can trigger this, if it's worth to handle
+ optimally, and if we can handle it optimally. */
+ }
+ }
+ else
+ {
+ gcc_assert (TREE_CODE (nit) == SSA_NAME);
+
+ gimple def = SSA_NAME_DEF_STMT (nit);
+
+ if (def
+ && is_gimple_assign (def)
+ && gimple_assign_rhs_code (def) == PLUS_EXPR)
+ {
+ tree op1 = gimple_assign_rhs1 (def);
+ tree op2 = gimple_assign_rhs2 (def);
+ if (integer_minus_onep (op1))
+ alt_bound = op2;
+ else if (integer_minus_onep (op2))
+ alt_bound = op1;
+ }
+
+ /* There is a number of test-cases for which we don't get an alt_bound
+ here: they're listed here, with the lhs of the last stmt as the nit:
+
+ libgomp.graphite/force-parallel-1.c:
+ _21 = (signed long) N_6(D);
+ _19 = _21 + -1;
+ _7 = (unsigned long) _19;
+
+ libgomp.graphite/force-parallel-2.c:
+ _33 = (signed long) N_9(D);
+ _16 = _33 + -1;
+ _37 = (unsigned long) _16;
+
+ libgomp.graphite/force-parallel-5.c:
+ <bb 6>:
+ # graphite_IV.5_46 = PHI <0(5), graphite_IV.5_47(11)>
+ <bb 7>:
+ _33 = (unsigned long) graphite_IV.5_46;
+
+ g++.dg/tree-ssa/pr34355.C:
+ _2 = (unsigned int) i_9;
+ _3 = 4 - _2;
+
+ gcc.dg/pr53849.c:
+ _5 = d.0_11 + -2;
+ _18 = (unsigned int) _5;
+
+ We will be able to handle some of these cases, if we can determine when
+ it's safe to look past casts. */
+ }
+
+ if (alt_bound == NULL_TREE)
+ return false;
+
+ transform_to_exit_first_loop_alt (loop, reduction_list, alt_bound);
+ return true;
+}
+
+/* Moves the exit condition of LOOP to the beginning of its header. NIT is the
+ number of iterations of the loop. REDUCTION_LIST describes the reductions in
+ LOOP. */
static void
transform_to_exit_first_loop (struct loop *loop,
@@ -1961,8 +2331,19 @@ gen_parallel_loop (struct loop *loop,
/* Base all the induction variables in LOOP on a single control one. */
canonicalize_loop_ivs (loop, &nit, true);
- /* Ensure that the exit condition is the first statement in the loop. */
- transform_to_exit_first_loop (loop, reduction_list, nit);
+ /* Ensure that the exit condition is the first statement in the loop.
+ The common case is that latch of the loop is empty (apart from the
+ increment) and immediately follows the loop exit test. Attempt to move the
+ entry of the loop directly before the exit check and increase the number of
+ iterations of the loop by one. */
+ if (!try_transform_to_exit_first_loop_alt (loop, reduction_list, nit))
+ {
+ /* Fall back on the method that handles more cases, but duplicates the
+ loop body: move the exit condition of LOOP to the beginning of its
+ header, and duplicate the part of the last iteration that gets disabled
+ to the exit of the loop. */
+ transform_to_exit_first_loop (loop, reduction_list, nit);
+ }
/* Generate initializations for reductions. */
if (reduction_list->elements () > 0)
diff --git a/libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt-2.c b/libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt-2.c
new file mode 100644
index 0000000..eb5e11f
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt-2.c
@@ -0,0 +1,48 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -ftree-parallelize-loops=2" } */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define N 1000
+
+unsigned int a[N];
+unsigned int b[N];
+unsigned int c[N];
+
+void __attribute__((noclone,noinline))
+f (void)
+{
+ int i;
+
+ for (i = 0; i < N; ++i)
+ c[i] = a[i] + b[i];
+}
+
+int
+main (void)
+{
+ int i, j;
+
+ /* Complexify loop to inhibit parloops. */
+ for (j = 0; j < 100; ++j)
+ for (i = 0; i < 10; i++)
+ {
+ int k = i + (10 * j);
+ a[k] = k;
+ b[k] = (k * 3) % 7;
+ c[k] = k * 2;
+ }
+
+ f ();
+
+ for (i = 0; i < N; i++)
+ {
+ unsigned int actual = c[i];
+ unsigned int expected = i + ((i * 3) % 7);
+ if (actual != expected)
+ abort ();
+ }
+
+ return 0;
+}
diff --git a/libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt-3.c b/libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt-3.c
new file mode 100644
index 0000000..b426b3f
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt-3.c
@@ -0,0 +1,29 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -ftree-parallelize-loops=2" } */
+
+unsigned int *a;
+
+unsigned int __attribute__((noclone,noinline))
+f (unsigned int n)
+{
+ int i;
+ unsigned int sum = 1;
+
+ for (i = 0; i < n; ++i)
+ sum += a[i];
+
+ return sum;
+}
+
+int
+main (void)
+{
+ unsigned int res;
+ unsigned int array[4000];
+ int i;
+ for (i = 0; i < 4000; ++i)
+ array[i] = i % 7;
+ a = &array[0];
+ res = f (4000);
+ return !(res == 11995);
+}
diff --git a/libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt.c b/libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt.c
new file mode 100644
index 0000000..d7d4003
--- /dev/null
+++ b/libgomp/testsuite/libgomp.c/parloops-exit-first-loop-alt.c
@@ -0,0 +1,48 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -ftree-parallelize-loops=2" } */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define N 1000
+
+unsigned int a[N];
+unsigned int b[N];
+unsigned int c[N];
+
+void __attribute__((noclone,noinline))
+f (unsigned int n)
+{
+ int i;
+
+ for (i = 0; i < n; ++i)
+ c[i] = a[i] + b[i];
+}
+
+int
+main (void)
+{
+ int i, j;
+
+ /* Complexify loop to inhibit parloops. */
+ for (j = 0; j < 100; ++j)
+ for (i = 0; i < 10; i++)
+ {
+ int k = i + (10 * j);
+ a[k] = k;
+ b[k] = (k * 3) % 7;
+ c[k] = k * 2;
+ }
+
+ f (N);
+
+ for (i = 0; i < N; i++)
+ {
+ unsigned int actual = c[i];
+ unsigned int expected = i + ((i * 3) % 7);
+ if (actual != expected)
+ abort ();
+ }
+
+ return 0;
+}
--
1.9.1
