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Commit e7e7f402 by Jeff Law Committed by Jeff Law
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tree-ssa-threadupdate.c: Include tree-cfg.h and tree-pass.h 

	* tree-ssa-threadupdate.c: Include tree-cfg.h and tree-pass.h
	(thread_block_1): Do not cancel jump threads which go from
	inside a loop, through the header, then back inside the loop.
	(bb_ends_with_multiway_branch): New function.
	(thread_through_all_blocks): Handle threading cases which start
	in a loop through the loop header to a point in the loop.

From-SVN: r205246
parent e44a45c6
Showing with 117 additions and 38 deletions
gcc/ChangeLog
2013-11-22 Jeff Law <law@redhat.com>
* tree-ssa-threadupdate.c: Include tree-cfg.h and tree-pass.h
(thread_block_1): Do not cancel jump threads which go from
inside a loop, through the header, then back inside the loop.
(bb_ends_with_multiway_branch): New function.
(thread_through_all_blocks): Handle threading cases which start
in a loop through the loop header to a point in the loop.
* tree-ssa-threadedge.c (thread_across_edge): Mark the start of the
jump thread path properly.
gcc/tree-ssa-threadupdate.c
......@@ -35,6 +35,8 @@ along with GCC; see the file COPYING3. If not see
#include "cfgloop.h"
#include "hash-table.h"
#include "dbgcnt.h"
#include "tree-cfg.h"
#include "tree-pass.h"
/* Given a block B, update the CFG and SSA graph to reflect redirecting
one or more in-edges to B to instead reach the destination of an
......@@ -815,29 +817,15 @@ thread_block_1 (basic_block bb, bool noloop_only, bool joiners)
}
/* Another case occurs when trying to thread through our
own loop header, possibly from inside the loop.
If our loop header is buried in the path, then go ahead
and cancel the jump threading request here. This likely
will need updating for the FSA/FSM coremark case.
Other cases (BB is the loop header) are handled elsewhere. */
own loop header, possibly from inside the loop. We will
thread these later. */
unsigned int i;
for (i = 1; i < path->length (); i++)
{
if ((*path)[i]->e->src == bb->loop_father->header
&& (!loop_exit_edge_p (bb->loop_father, e2)
|| (*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK))
{
/* If i != 1, then it's a buried header that will not
be handled elsehwere. */
if (i != 1)
{
delete_jump_thread_path (path);
e->aux = NULL;
}
break;
}
break;
}
if (i != path->length ())
......@@ -1554,6 +1542,20 @@ mark_threaded_blocks (bitmap threaded_blocks)
}
/* Return TRUE if BB ends with a switch statement or a computed goto.
Otherwise return false. */
static bool
bb_ends_with_multiway_branch (basic_block bb ATTRIBUTE_UNUSED)
{
gimple stmt = last_stmt (bb);
if (stmt && gimple_code (stmt) == GIMPLE_SWITCH)
return true;
if (stmt && gimple_code (stmt) == GIMPLE_GOTO
&& TREE_CODE (gimple_goto_dest (stmt)) == SSA_NAME)
return true;
return false;
}
/* Walk through all blocks and thread incoming edges to the appropriate
outgoing edge for each edge pair recorded in THREADED_EDGES.
......@@ -1573,6 +1575,7 @@ thread_through_all_blocks (bool may_peel_loop_headers)
bitmap_iterator bi;
bitmap threaded_blocks;
struct loop *loop;
bool totally_clobbered_loops = false;
/* We must know about loops in order to preserve them. */
gcc_assert (current_loops != NULL);
......@@ -1609,35 +1612,79 @@ thread_through_all_blocks (bool may_peel_loop_headers)
retval |= thread_through_loop_header (loop, may_peel_loop_headers);
}
/* Assume we had a jump thread path which went from the latch to the exit
and a path which goes from outside to inside the same loop.
If the latch to exit was handled first, we will thread it and clear
loop->header.
The second path will be ignored by thread_block because we're going
through a loop header. It will also be ignored by the loop above
because loop->header is NULL.
This results in the second path never being threaded. The failure
mode is a dangling AUX field.
This is inherently a bit of a pain to fix, so we just walk all the
blocks and all the incoming edges to those blocks and clear their
AUX fields. */
/* Any jump threading paths that are still attached to edges at this
point must be one of two cases.
First, we could have a jump threading path which went from outside
a loop to inside a loop that was ignored because a prior jump thread
across a backedge was realized (which indirectly causes the loop
above to ignore the latter thread). We can detect these because the
loop structures will be different and we do not currently try to
optimize this case.
Second, we could be threading across a backedge to a point within the
same loop. This occurrs for the FSA/FSM optimization and we would
like to optimize it. However, we have to be very careful as this
may completely scramble the loop structures, with the result being
irreducible loops causing us to throw away our loop structure.
As a compromise for the latter case, if the thread path ends in
a block where the last statement is a multiway branch, then go
ahead and thread it, else ignore it. */
basic_block bb;
edge_iterator ei;
edge e;
FOR_EACH_BB (bb)
{
FOR_EACH_EDGE (e, ei, bb->preds)
/* If we do end up threading here, we can remove elements from
BB->preds. Thus we can not use the FOR_EACH_EDGE iterator. */
for (edge_iterator ei = ei_start (bb->preds);
(e = ei_safe_edge (ei));)
if (e->aux)
{
vec<jump_thread_edge *> *path = THREAD_PATH (e);
delete_jump_thread_path (path);
e->aux = NULL;
/* Case 1, threading from outside to inside the loop
after we'd already threaded through the header. */
if ((*path)[0]->e->dest->loop_father
!= path->last ()->e->src->loop_father)
{
delete_jump_thread_path (path);
e->aux = NULL;
ei_next (&ei);
}
else if (bb_ends_with_multiway_branch (path->last ()->e->src))
{
/* The code to thread through loop headers may have
split a block with jump threads attached to it.
We can identify this with a disjoint jump threading
path. If found, just remove it. */
for (unsigned int i = 0; i < path->length () - 1; i++)
if ((*path)[i]->e->dest != (*path)[i + 1]->e->src)
{
delete_jump_thread_path (path);
e->aux = NULL;
ei_next (&ei);
break;
}
/* Our path is still valid, thread it. */
if (e->aux)
{
totally_clobbered_loops
|= thread_block ((*path)[0]->e->dest, false);
e->aux = NULL;
}
}
else
{
delete_jump_thread_path (path);
e->aux = NULL;
ei_next (&ei);
}
}
else
ei_next (&ei);
}
statistics_counter_event (cfun, "Jumps threaded",
......@@ -1649,7 +1696,32 @@ thread_through_all_blocks (bool may_peel_loop_headers)
threaded_blocks = NULL;
paths.release ();
if (retval)
/* If we made changes to the CFG that might have totally messed
up the loop structure, then drop the old loop structure and
rebuild. */
if (totally_clobbered_loops)
{
/* Release the current loop structures, they are totally
clobbered at this point. */
loop_optimizer_finalize ();
current_loops = NULL;
/* Similarly for dominance information. */
free_dominance_info (CDI_DOMINATORS);
free_dominance_info (CDI_POST_DOMINATORS);
/* Before we can rebuild the loop structures, we need dominators,
which requires no unreachable code. So remove unreachable code. */
delete_unreachable_blocks ();
/* Now rebuild the loop structures. */
cfun->curr_properties &= ~PROP_loops;
loop_optimizer_init (AVOID_CFG_MODIFICATIONS);
cfun->curr_properties |= PROP_loops;
retval = 1;
}
if (retval && current_loops)
loops_state_set (LOOPS_NEED_FIXUP);
return retval;
......
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