On Fri, Oct 18, 2013 at 7:12 PM, Jeff Law <l...@redhat.com> wrote:
>
>
> Back in 2011 I wrote code to detect cases when traversing a particular path
> could be proven to trigger undefined behaviour (such as a null pointer
> dereference). That original patch would find the control dependent edges
> leading to the dereference and eliminate those edges. The result being those
> paths with undefined behaviour simply vanished.
>
> The problem with that implementation is there could have been observable
> side effects on those paths prior to triggering the undefined behaviour.
>
> At that time I speculated we could isolate the path (via block copying) with
> undefined behaviour. On the duplicate path we'd replace the undefined
> behaviour with a trap and remove only the outgoing edges. That would still
> preserve any visible side effects on the undefined path up to the undefined
> behaviour and we still often get to simplify the main path, though not as
> much as the original version from 2011.
>
> That's precisely what this patch does. When we have a PHI which feeds a
> memory dereference in the same block as the PHI and one (or more) of the PHI
> args is NULL we duplicate the block, redirect incoming edges with the NULL
> PHI args to the duplicate and change the statement with the memory
> dereference to a trap.
>
> You can certainly ask is this actually helpful. In my experience, yes. I'm
> regularly seeing stuff like
>
> x2 = PHI (x1, x1, 0, 0);
> *x2
>
> When we isolate the paths with NULL incoming values, we're left with
> x2 = PHI (x1, x1)
>
> And we can propagate x1 into uses of x2. The block now has just one pred
> and the current block can sometimes be merged into that single pred. I've
> seen the combination of those two then lead to identification additional
> common subexpressions.
>
> You might also ask how often such paths show up. In a bootstrap about a
> week ago, this triggered ~3500 times.
>
> The code tries to be reasonably smart and re-use an existing duplicate when
> there's multiple NULL values in a PHI node. That triggers often enough to
> be worth the marginal amount of book keeping.
>
> The code doesn't yet handle the case where there's multiple dereferences in
> the block. There's no guarantee the first dereference will be the first one
> we find on the immediate use list. It's on my TODO list.
>
>
> There's no reason this same framework couldn't be used to do the same thing
> for an out of bounds array access. Similarly, it wouldn't be hard to issue
> a warning when these transformations are applied.
>
> Posting at this time to get some feedback. Planning a formal RFA prior to
> close of 4.9 stage1.
>
> And, of course, this bootstrapps and regression tests. 20030711-3 is
> clearly optimized further with this patch, but I'll cobble together some
> more testcases next week.
>
>
> I'm not familiar with the options stuff, so if someone could look at that
> more closely, I'd appreciate it. Similarly for the bits to create a new
> pass structure.
>
>
> Thoughts, comments, flames?
I wonder why this isn't part of the regular jump-threading code - after
all the opportunity is to thead to __builtin_unreachable () ;) Otherwise
the question is always where you'd place this pass and whether it
enables jump threading or CSE opportunities (that at least it does).
Richard.
>
>
>
>
>
> * Makefile.in (OBJS): Add tree-ssa-isolate-paths.
> * common.opt (-ftree-isolate-paths): Add option and documentation.
> * opts.c (default_options_table): Add OPT_ftree_isolate_paths.
> * passes.def: Add path isolation pass.
> * timevar.def (TV_TREE_SSA_ISOLATE_PATHS): New timevar.
> * tree-pass.h (make_isolate_paths): Declare.
> * tree-ssa-isolate-paths.c: New file.
>
> * gcc.dg/pr38984.c: Add -fno-tree-isolate-paths.
> * gcc.dg/tree-ssa/20030711-3.c: Update expected output.
>
> * testsuite/libmudflap.c/fail20-frag.c: Add -fno-tree-isolate-paths.
>
>
> diff --git a/gcc/Makefile.in b/gcc/Makefile.in
> index ba39ac9..e7c18bc 100644
> --- a/gcc/Makefile.in
> +++ b/gcc/Makefile.in
> @@ -1412,6 +1412,7 @@ OBJS = \
> tree-ssa-dse.o \
> tree-ssa-forwprop.o \
> tree-ssa-ifcombine.o \
> + tree-ssa-isolate-paths.o \
> tree-ssa-live.o \
> tree-ssa-loop-ch.o \
> tree-ssa-loop-im.o \
> diff --git a/gcc/common.opt b/gcc/common.opt
> index 1f11fcd..1fd1bcc 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -2104,6 +2104,12 @@ foptimize-strlen
> Common Report Var(flag_optimize_strlen) Optimization
> Enable string length optimizations on trees
>
> +ftree-isolate-paths
> +Common Report Var(flag_tree_isolate_paths) Init(1) Optimization
> +Detect paths which trigger undefined behaviour. Isolate those paths from
> +the main control flow and turn the statement with undefined behaviour into
> +a trap.
> +
> ftree-loop-distribution
> Common Report Var(flag_tree_loop_distribution) Optimization
> Enable loop distribution on trees
> diff --git a/gcc/opts.c b/gcc/opts.c
> index 728d36d..b6ed0c2 100644
> --- a/gcc/opts.c
> +++ b/gcc/opts.c
> @@ -453,6 +453,7 @@ static const struct default_options
> default_options_table[] =
> { OPT_LEVELS_1_PLUS, OPT_ftree_ch, NULL, 1 },
> { OPT_LEVELS_1_PLUS, OPT_fcombine_stack_adjustments, NULL, 1 },
> { OPT_LEVELS_1_PLUS, OPT_fcompare_elim, NULL, 1 },
> + { OPT_LEVELS_1_PLUS, OPT_ftree_isolate_paths, NULL, 1 },
> { OPT_LEVELS_1_PLUS, OPT_ftree_slsr, NULL, 1 },
>
> /* -O2 optimizations. */
> diff --git a/gcc/passes.def b/gcc/passes.def
> index 84eb3f3..1f2c810 100644
> --- a/gcc/passes.def
> +++ b/gcc/passes.def
> @@ -173,6 +173,13 @@ along with GCC; see the file COPYING3. If not see
> only examines PHIs to discover const/copy propagation
> opportunities. */
> NEXT_PASS (pass_phi_only_cprop);
> + /* At this point the majority of const/copy propagations
> + are exposed. Go ahead and identify paths that should never
> + be executed in a conforming program and isolate those paths.
> +
> + This will simplify the CFG in the main path and provide PRE
> + DOM and other passes additional opportunities to optimize. */
> + NEXT_PASS (pass_isolate_paths);
> NEXT_PASS (pass_dse);
> NEXT_PASS (pass_reassoc);
> NEXT_PASS (pass_dce);
> diff --git a/gcc/testsuite/gcc.dg/pr38984.c b/gcc/testsuite/gcc.dg/pr38984.c
> index 11f1e7f..196ca39 100644
> --- a/gcc/testsuite/gcc.dg/pr38984.c
> +++ b/gcc/testsuite/gcc.dg/pr38984.c
> @@ -1,5 +1,5 @@
> /* { dg-do compile } */
> -/* { dg-options "-O2 -fno-delete-null-pointer-checks -fdump-tree-optimized"
> }
> +/* { dg-options "-O2 -fno-delete-null-pointer-checks -fdump-tree-optimized
> -fno-tree-isolate-paths" }
> * */
>
> int f(int *p)
> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/20030711-3.c
> b/gcc/testsuite/gcc.dg/tree-ssa/20030711-3.c
> index ec04e17..bcd5681 100644
> --- a/gcc/testsuite/gcc.dg/tree-ssa/20030711-3.c
> +++ b/gcc/testsuite/gcc.dg/tree-ssa/20030711-3.c
> @@ -52,10 +52,10 @@ get_alias_set (t)
> /* There should be one load of decl.rtl. */
> /* { dg-final { scan-tree-dump-times "decl\\.rtl" 1 "dom2"} } */
>
> -/* There should be two loads of rtmem. */
> -/* { dg-final { scan-tree-dump-times "rtmem" 2 "dom2"} } */
> +/* There should be one load of rtmem. */
> +/* { dg-final { scan-tree-dump-times "rtmem" 1 "dom2"} } */
>
> -/* There should be one load of alias. */
> -/* { dg-final { scan-tree-dump-times "->alias" 1 "dom2"} } */
> +/* There should be no load of alias. */
> +/* { dg-final { scan-tree-dump-not "->alias" "dom2"} } */
>
> /* { dg-final { cleanup-tree-dump "dom2" } } */
> diff --git a/gcc/timevar.def b/gcc/timevar.def
> index 5a880a8..119bd95 100644
> --- a/gcc/timevar.def
> +++ b/gcc/timevar.def
> @@ -144,6 +144,7 @@ DEFTIMEVAR (TV_TREE_SSA_INCREMENTAL , "tree SSA
> incremental")
> DEFTIMEVAR (TV_TREE_OPS , "tree operand scan")
> DEFTIMEVAR (TV_TREE_SSA_DOMINATOR_OPTS , "dominator optimization")
> DEFTIMEVAR (TV_TREE_SRA , "tree SRA")
> +DEFTIMEVAR (TV_TREE_SSA_ISOLATE_PATHS , "tree SSA isolate paths")
> DEFTIMEVAR (TV_TREE_CCP , "tree CCP")
> DEFTIMEVAR (TV_TREE_PHI_CPROP , "tree PHI const/copy prop")
> DEFTIMEVAR (TV_TREE_SPLIT_EDGES , "tree split crit edges")
> diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h
> index e72fe9a..30a3afd 100644
> --- a/gcc/tree-pass.h
> +++ b/gcc/tree-pass.h
> @@ -427,6 +427,7 @@ extern gimple_opt_pass *make_pass_sink_code
> (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_fre (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_check_data_deps (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_copy_prop (gcc::context *ctxt);
> +extern gimple_opt_pass *make_pass_isolate_paths (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_vrp (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_uncprop (gcc::context *ctxt);
> extern gimple_opt_pass *make_pass_return_slot (gcc::context *ctxt);
> diff --git a/libmudflap/testsuite/libmudflap.c/fail20-frag.c
> b/libmudflap/testsuite/libmudflap.c/fail20-frag.c
> index 0dd8bb7..54200cc 100644
> --- a/libmudflap/testsuite/libmudflap.c/fail20-frag.c
> +++ b/libmudflap/testsuite/libmudflap.c/fail20-frag.c
> @@ -11,3 +11,4 @@ return 0;
> /* { dg-output "Nearby object 1.*" } */
> /* { dg-output "mudflap object.*.NULL.*" } */
> /* { dg-do run { xfail *-*-* } } */
> +/* { dg-options "-lmudflap -fmudflap -fno-tree-isolate-paths" } */
> *** /dev/null Mon Sep 30 09:08:45 2013
> --- tree-ssa-isolate-paths.c Thu Oct 17 15:38:23 2013
> ***************
> *** 0 ****
> --- 1,399 ----
> + /* Detect paths through the CFG which can never be executed in a
> conforming
> + program and isolate them.
> +
> + Copyright (C) 2013
> + Free Software Foundation, Inc.
> +
> + This file is part of GCC.
> +
> + GCC is free software; you can redistribute it and/or modify
> + it under the terms of the GNU General Public License as published by
> + the Free Software Foundation; either version 3, or (at your option)
> + any later version.
> +
> + GCC is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + GNU General Public License for more details.
> +
> + You should have received a copy of the GNU General Public License
> + along with GCC; see the file COPYING3. If not see
> + <http://www.gnu.org/licenses/>. */
> +
> + #include "config.h"
> + #include "system.h"
> + #include "coretypes.h"
> + #include "tm.h"
> + #include "tree.h"
> + #include "flags.h"
> + #include "tm_p.h"
> + #include "basic-block.h"
> + #include "output.h"
> + #include "function.h"
> + #include "tree-pretty-print.h"
> + #include "gimple-pretty-print.h"
> + #include "timevar.h"
> + #include "tree-dump.h"
> + #include "tree-flow.h"
> + #include "tree-pass.h"
> + #include "tree-ssa.h"
> + #include "tree-ssa-propagate.h"
> + #include "langhooks.h"
> + #include "cfgloop.h"
> +
> +
> + /* Note if we've optimized anything and thus want to run CFG cleanups
> + when this pass is complete. Obviously if this pass does nothing, then
> + CFG cleanups would be a waste of time. */
> + bool cfg_altered;
> +
> + /* BB when reached via incoming edge E will exhibit undefined behaviour
> + at STMT. Isolate and optimize the path which exhibits undefined
> + behaviour.
> +
> + Isolation is simple. Duplicate BB and redirect E to BB'.
> +
> + Optimization is simple as well. Replace STMT in BB' with an
> + unconditional trap and remove all outgoing edges from BB'.
> +
> + DUPLICATE is a pre-existing duplicate, use it as BB' if it exists.
> +
> + Return BB'. */
> +
> + basic_block
> + isolate_path (basic_block bb, basic_block duplicate, edge e, gimple stmt)
> + {
> + gimple_stmt_iterator si, si2;
> + edge_iterator ei;
> + edge e2;
> +
> +
> + /* First duplicate BB if we have not done so already and remove all
> + the duplicate's outgoing edges as duplicate is going to
> unconditionally
> + trap. Removing the outgoing edges is both an optimization and
> ensures
> + we don't need to do any PHI node updates. */
> + if (!duplicate)
> + {
> + duplicate = duplicate_block (bb, NULL, NULL);
> + for (ei = ei_start (duplicate->succs); (e2 = ei_safe_edge (ei)); )
> + remove_edge (e2);
> + }
> +
> + /* Complete the isolation step by redirecting E to reach DUPLICATE. */
> + e2 = redirect_edge_and_branch (e, duplicate);
> + flush_pending_stmts (e2);
> +
> +
> + /* There may be more than one statement in DUPLICATE which exhibits
> + undefined behaviour. Ultimately we want the first such statement in
> + DUPLCIATE so that we're able to delete as much code as possible.
> +
> + So each time we discover undefined behaviour in DUPLICATE, search for
> + the statement which triggers undefined behaviour. If found, then
> transform
> + the statement into a trap and delete everything after the statement.
> If
> + not found, then this particular instance was subsumed by an earlier
> instance
> + of undefined behaviour and there's nothing to do.
> +
> + This is made more complicated by the fact that we have STMT, which is
> in BB
> + rather than in DUPLICATE. So we set up two iterators, one for each
> block and
> + walk forward looking for STMT in BB, advancing each iterator at each
> step.
> +
> + When we find STMT the second iterator should point to STMT's
> equivalent in
> + duplicate. If DUPLICATE ends before STMT is found in BB, then
> there's nothing
> + to do.
> +
> + Ignore labels and debug statements. */
> + for (si = gsi_start_nondebug_bb (bb), si2 = gsi_start_nondebug_bb
> (duplicate);
> + !gsi_end_p (si) && !gsi_end_p (si2);
> + gsi_next_nondebug (&si), gsi_next_nondebug (&si2))
> + {
> + while (gimple_code (gsi_stmt (si)) == GIMPLE_LABEL)
> + gsi_next_nondebug (&si);
> + while (gimple_code (gsi_stmt (si2)) == GIMPLE_LABEL)
> + gsi_next_nondebug (&si2);
> + if (gsi_stmt (si) == stmt)
> + break;
> + }
> +
> + /* This would be an indicator that we never found STMT in BB, which
> should
> + never happen. */
> + gcc_assert (!gsi_end_p (si));
> +
> + /* If we did not run to the end of DUPLICATE, then SI points to STMT and
> + SI2 points to the duplicate of STMT in DUPLICATE. */
> + if (!gsi_end_p (si2))
> + {
> + /* SI2 is the iterator in the duplicate block and it now points
> + to our victim statement. */
> + gimple_seq seq = NULL;
> + tree t = build_call_expr_loc (0,
> + builtin_decl_explicit (BUILT_IN_TRAP),
> 0);
> + gimplify_and_add (t, &seq);
> + gsi_insert_before (&si2, seq, GSI_SAME_STMT);
> +
> + /* Now delete all remaining statements in this block. */
> + for (; !gsi_end_p (si2);)
> + gsi_remove (&si2, true);
> + }
> +
> + return duplicate;
> + }
> +
> + /* Search the function for statements which, if executed, would cause
> + the program to fault such as a dereference of a NULL pointer.
> +
> + Such a program can't be valid if such a statement was to execute
> + according to ISO standards.
> +
> + We detect explicit NULL pointer dereferences as well as those implied
> + by a PHI argument having a NULL value which unconditionally flows into
> + a dereference in the same block as the PHI.
> +
> + In the former case we replace the offending statement with an
> + unconditional trap and eliminate the outgoing edges from the
> statement's
> + basic block. This may expose secondary optimization opportunities.
> +
> + In the latter case, we isolate the path(s) with the NULL PHI
> + feeding the dereference. We can then replace the offending statement
> + and eliminate the outgoing edges in the duplicate. Again, this may
> + expose secondary optimization opportunities.
> +
> + A warning for both cases may be advisable as well.
> +
> + Other statically detectable violations of the ISO standard could be
> + handled in a similar way, such as out-of-bounds array indexing. */
> +
> + static unsigned int
> + tree_ssa_isolate_paths (void)
> + {
> + basic_block bb;
> +
> + initialize_original_copy_tables ();
> +
> + /* Search all the blocks for edges which, if traversed, will
> + result in undefined behaviour. */
> + cfg_altered = false;
> + FOR_EACH_BB (bb)
> + {
> + gimple_stmt_iterator si;
> +
> + /* First look for a PHI which sets a pointer to NULL and which
> + is then dereferenced within BB. This is somewhat overly
> + conservative, but probably catches most of the interesting
> + cases. */
> + for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si))
> + {
> + gimple phi = gsi_stmt (si);
> + tree lhs = gimple_phi_result (phi);
> +
> + /* If the result is not a pointer, then there is no need to
> + examine the arguments. */
> + if (!POINTER_TYPE_P (TREE_TYPE (lhs)))
> + continue;
> +
> + /* PHI produces a pointer result. See if any of the PHI's
> + arguments are NULL.
> +
> + When we remove an edge, we want to reprocess the current
> + index, hence the ugly way we update I for each iteration. */
> + basic_block duplicate = NULL;
> + for (unsigned i = 0, next_i = 0; i < gimple_phi_num_args (phi); i
> = next_i)
> + {
> + tree op = gimple_phi_arg_def (phi, i);
> +
> + next_i = i + 1;
> + if (operand_equal_p (op, integer_zero_node, 0))
> + {
> + gimple use_stmt;
> + imm_use_iterator iter;
> +
> + /* We've got a NULL PHI argument. Now see if the
> + PHI's result is dereferenced within BB. */
> + FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs)
> + {
> + unsigned int j;
> + bool removed_edge = false;
> +
> + /* We only care about uses in BB which are
> assignements
> + with memory operands.
> +
> + We could see if any uses are as function arguments
> + when the callee has marked the argument as being
> + non-null. */
> + if (gimple_bb (use_stmt) != bb
> + || !gimple_has_mem_ops (use_stmt)
> + || gimple_code (use_stmt) != GIMPLE_ASSIGN)
> + continue;
> +
> + /* Look at each operand for a memory reference using
> + LHS. */
> + for (j = 0; j < gimple_num_ops (use_stmt); j++)
> + {
> + tree op = gimple_op (use_stmt, j);
> +
> + if (op == NULL)
> + continue;
> +
> + while (handled_component_p (op))
> + op = TREE_OPERAND (op, 0);
> +
> + if ((TREE_CODE (op) == MEM_REF
> + || TREE_CODE (op) == INDIRECT_REF)
> + && TREE_OPERAND (op, 0) == lhs)
> + {
> + edge e = gimple_phi_arg_edge (phi, i);
> + duplicate = isolate_path (bb, duplicate,
> + e, use_stmt);
> +
> + /* When we remove an incoming edge, we need to
> + reprocess the Ith element. */
> + next_i = i;
> +
> + removed_edge = true;
> + cfg_altered = true;
> + break;
> + }
> + }
> +
> + /* We really want to process other immediate uses
> here.
> + There may be another immediate use of LHS in this
> + block prior to the one we just turned into a trap.
> +
> + However, for now, we ignore other immediate uses.
> */
> + if (removed_edge)
> + BREAK_FROM_IMM_USE_STMT (iter);
> + }
> + }
> + }
> + }
> +
> + /* Now look at the statements in the block and see if any of
> + them explicitly dereference a NULL pointer. Believe it or
> + not, this does happen from time to time. */
> + bool found = false;
> + for (si = gsi_start_bb (bb); !gsi_end_p (si); gsi_next (&si))
> + {
> + gimple stmt = gsi_stmt (si);
> + unsigned int i;
> +
> + /* We only care about assignments with memory operands.
> +
> + Again, we could see if any uses are as function arguments
> + when the callee has marked the argument as being non-null. */
> + if (!gimple_has_mem_ops (stmt)
> + || gimple_code (stmt) != GIMPLE_ASSIGN)
> + continue;
> +
> + /* Look at each operand for a memory reference using an explicit
> + NULL pointer. */
> + for (i = 0; i < gimple_num_ops (stmt); i++)
> + {
> + tree op = gimple_op (stmt, i);
> +
> + if (op == NULL)
> + continue;
> +
> + while (handled_component_p (op))
> + op = TREE_OPERAND (op, 0);
> +
> + if (TREE_CODE (op) == MEM_REF || TREE_CODE (op) ==
> INDIRECT_REF)
> + {
> + tree op0 = TREE_OPERAND (op, 0);
> + /* If the operand is NULL, then this block will trigger
> undefined
> + behaviour at runtime if we reach STMT. */
> + if (operand_equal_p (op0, integer_zero_node, 0))
> + {
> + /* First insert a TRAP before this statement. */
> + gimple_seq seq = NULL;
> + tree t
> + = build_call_expr_loc (0,builtin_decl_explicit
> (BUILT_IN_TRAP), 0);
> + gimplify_and_add (t, &seq);
> + gsi_insert_before (&si, seq, GSI_SAME_STMT);
> +
> + /* Now delete all remaining statements in this block.
> */
> + for (gimple_stmt_iterator si2 = si; !gsi_end_p (si2);)
> + gsi_remove (&si2, true);
> +
> + /* And finally, remove all outgoing edges from BB. */
> + edge e;
> + for (edge_iterator ei = ei_start (bb->succs);
> + (e = ei_safe_edge (ei)); )
> + remove_edge (e);
> +
> + /* Ignore any more operands on this statement and
> + continue the statement iterator (which should
> + terminate its loop immediately. */
> + found = true;
> + cfg_altered = true;
> + break;
> + }
> + }
> + }
> +
> + if (found)
> + break;
> + }
> + }
> + free_original_copy_tables ();
> +
> + /* We scramble the CFG and loop structures a bit, clean up
> + appropriately. We really should incrementally update the
> + loop structures, in theory it shouldn't be that hard. */
> + if (cfg_altered)
> + {
> + free_dominance_info (CDI_DOMINATORS);
> + free_dominance_info (CDI_POST_DOMINATORS);
> + loops_state_set (LOOPS_NEED_FIXUP);
> + return TODO_cleanup_cfg | TODO_update_ssa;
> + }
> + return 0;
> + }
> +
> + static bool
> + gate_isolate_paths (void)
> + {
> + /* If we do not have a suitable builtin function for the trap statement,
> + then do not perform the optimization. */
> + return (flag_tree_isolate_paths != 0
> + && builtin_decl_explicit (BUILT_IN_TRAP) != NULL);
> +
> + }
> +
> + namespace {
> + const pass_data pass_data_isolate_paths =
> + {
> + GIMPLE_PASS, /* type */
> + "isolatepaths", /* name */
> + OPTGROUP_NONE, /* optinfo_flags */
> + true, /* has_gate */
> + true, /* has_execute */
> + TV_TREE_SSA_ISOLATE_PATHS, /* tv_id */
> + ( PROP_cfg | PROP_ssa ), /* properties_required */
> + 0, /* properties_provided */
> + 0, /* properties_destroyed */
> + 0, /* todo_flags_start */
> + TODO_verify_ssa, /* todo_flags_finish */
> + };
> +
> + class pass_isolate_paths : public gimple_opt_pass
> + {
> + public:
> + pass_isolate_paths (gcc::context *ctxt)
> + : gimple_opt_pass (pass_data_isolate_paths, ctxt)
> + {}
> +
> + /* opt_pass methods: */
> + opt_pass * clone () { return new pass_isolate_paths (m_ctxt); }
> + bool gate () { return gate_isolate_paths (); }
> + unsigned int execute () { return tree_ssa_isolate_paths (); }
> +
> + }; // class pass_uncprop
> + }
> +
> + gimple_opt_pass *
> + make_pass_isolate_paths (gcc::context *ctxt)
> + {
> + return new pass_isolate_paths (ctxt);
> + }
> +
> +
>
