/* Detect paths through the CFG which can never be executed in a conforming
program and isolate them.
- Copyright (C) 2013
- Free Software Foundation, Inc.
+ Copyright (C) 2013-2015 Free Software Foundation, Inc.
This file is part of GCC.
#include "config.h"
#include "system.h"
#include "coretypes.h"
+#include "alias.h"
+#include "symtab.h"
+#include "options.h"
#include "tree.h"
+#include "fold-const.h"
#include "flags.h"
+#include "predict.h"
+#include "tm.h"
+#include "hard-reg-set.h"
+#include "function.h"
+#include "dominance.h"
+#include "cfg.h"
#include "basic-block.h"
+#include "tree-ssa-alias.h"
+#include "internal-fn.h"
+#include "gimple-expr.h"
#include "gimple.h"
+#include "gimple-iterator.h"
+#include "gimple-walk.h"
#include "tree-ssa.h"
+#include "stringpool.h"
#include "tree-ssanames.h"
#include "gimple-ssa.h"
#include "tree-ssa-operands.h"
#include "ssa-iterators.h"
#include "cfgloop.h"
#include "tree-pass.h"
+#include "tree-cfg.h"
+#include "diagnostic-core.h"
+#include "intl.h"
static bool cfg_altered;
/* Callback for walk_stmt_load_store_ops.
-
+
Return TRUE if OP will dereference the tree stored in DATA, FALSE
otherwise.
This routine only makes a superficial check for a dereference. Thus,
it must only be used if it is safe to return a false negative. */
static bool
-check_loadstore (gimple stmt ATTRIBUTE_UNUSED, tree op, void *data)
+check_loadstore (gimple stmt, tree op, tree, void *data)
{
if ((TREE_CODE (op) == MEM_REF || TREE_CODE (op) == TARGET_MEM_REF)
&& operand_equal_p (TREE_OPERAND (op, 0), (tree)data, 0))
- return true;
+ {
+ TREE_THIS_VOLATILE (op) = 1;
+ TREE_SIDE_EFFECTS (op) = 1;
+ update_stmt (stmt);
+ return true;
+ }
return false;
}
code that wishes to catch the signal can do so.
If the dereference is a load, then there's nothing to do as the
- LHS will be a throw-away SSA_NAME and the LHS is the NULL dereference.
+ LHS will be a throw-away SSA_NAME and the RHS is the NULL dereference.
If the dereference is a store and we can easily transform the RHS,
- then simplify the RHS to enable more DCE. */
+ then simplify the RHS to enable more DCE. Note that we require the
+ statement to be a GIMPLE_ASSIGN which filters out calls on the RHS. */
gimple stmt = gsi_stmt (*si_p);
if (walk_stmt_load_store_ops (stmt, (void *)op, NULL, check_loadstore)
+ && is_gimple_assign (stmt)
&& INTEGRAL_TYPE_P (TREE_TYPE (gimple_assign_lhs (stmt))))
{
/* We just need to turn the RHS into zero converted to the proper
update_stmt (stmt);
}
- gimple new_stmt
+ gcall *new_stmt
= gimple_build_call (builtin_decl_explicit (BUILT_IN_TRAP), 0);
gimple_seq seq = NULL;
gimple_seq_add_stmt (&seq, new_stmt);
else
gsi_insert_before (si_p, seq, GSI_NEW_STMT);
- /* The iterator points to the __builtin_trap. Advance the iterator
- and delete everything else in the block. */
- gsi_next (si_p);
- for (; !gsi_end_p (*si_p);)
+ /* We must remove statements from the end of the block so that we
+ never reference a released SSA_NAME. */
+ basic_block bb = gimple_bb (gsi_stmt (*si_p));
+ for (gimple_stmt_iterator si = gsi_last_bb (bb);
+ gsi_stmt (si) != gsi_stmt (*si_p);
+ si = gsi_last_bb (bb))
{
- stmt = gsi_stmt (*si_p);
+ stmt = gsi_stmt (si);
unlink_stmt_vdef (stmt);
- gsi_remove (si_p, true);
+ gsi_remove (&si, true);
release_defs (stmt);
}
}
Optimization is simple as well. Replace STMT in BB' with an
unconditional trap and remove all outgoing edges from BB'.
+ If RET_ZERO, do not trap, only return NULL.
+
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, tree op)
+ edge e, gimple stmt, tree op, bool ret_zero)
{
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
if (!duplicate)
{
duplicate = duplicate_block (bb, NULL, NULL);
- for (ei = ei_start (duplicate->succs); (e2 = ei_safe_edge (ei)); )
- remove_edge (e2);
+ if (!ret_zero)
+ for (ei = ei_start (duplicate->succs); (e2 = ei_safe_edge (ei)); )
+ remove_edge (e2);
}
/* Complete the isolation step by redirecting E to reach DUPLICATE. */
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.
+ 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
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.
+ nothing to do.
Ignore labels and debug statements. */
si = gsi_start_nondebug_after_labels_bb (bb);
SI2 points to the duplicate of STMT in DUPLICATE. Insert a trap
before SI2 and remove SI2 and all trailing statements. */
if (!gsi_end_p (si2))
- insert_trap_and_remove_trailing_statements (&si2, op);
+ {
+ if (ret_zero)
+ {
+ greturn *ret = as_a <greturn *> (gsi_stmt (si2));
+ tree zero = build_zero_cst (TREE_TYPE (gimple_return_retval (ret)));
+ gimple_return_set_retval (ret, zero);
+ update_stmt (ret);
+ }
+ else
+ insert_trap_and_remove_trailing_statements (&si2, op);
+ }
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.
+/* Look for PHI nodes which feed statements in the same block where
+ the value of the PHI node implies the statement is erroneous.
- 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. */
+ For example, a NULL PHI arg value which then feeds a pointer
+ dereference.
-static unsigned int
-gimple_ssa_isolate_erroneous_paths (void)
+ When found isolate and optimize the path associated with the PHI
+ argument feeding the erroneous statement. */
+static void
+find_implicit_erroneous_behaviour (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)
+ FOR_EACH_BB_FN (bb, cfun)
{
- gimple_stmt_iterator si;
+ gphi_iterator si;
+
+ /* Out of an abundance of caution, do not isolate paths to a
+ block where the block has any abnormal outgoing edges.
+
+ We might be able to relax this in the future. We have to detect
+ when we have to split the block with the NULL dereference and
+ the trap we insert. We have to preserve abnormal edges out
+ of the isolated block which in turn means updating PHIs at
+ the targets of those abnormal outgoing edges. */
+ if (has_abnormal_or_eh_outgoing_edge_p (bb))
+ continue;
/* First look for a PHI which sets a pointer to NULL and which
is then dereferenced within BB. This is somewhat overly
cases. */
for (si = gsi_start_phis (bb); !gsi_end_p (si); gsi_next (&si))
{
- gimple phi = gsi_stmt (si);
+ gphi *phi = si.phi ();
tree lhs = gimple_phi_result (phi);
/* If the result is not a pointer, then there is no need to
continue;
/* PHI produces a pointer result. See if any of the PHI's
- arguments are NULL.
+ 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. */
i = next_i)
{
tree op = gimple_phi_arg_def (phi, i);
+ edge e = gimple_phi_arg_edge (phi, i);
+ imm_use_iterator iter;
+ gimple use_stmt;
next_i = i + 1;
-
+
+ if (TREE_CODE (op) == ADDR_EXPR)
+ {
+ tree valbase = get_base_address (TREE_OPERAND (op, 0));
+ if ((TREE_CODE (valbase) == VAR_DECL
+ && !is_global_var (valbase))
+ || TREE_CODE (valbase) == PARM_DECL)
+ {
+ FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs)
+ {
+ greturn *return_stmt
+ = dyn_cast <greturn *> (use_stmt);
+ if (!return_stmt)
+ continue;
+
+ if (gimple_return_retval (return_stmt) != lhs)
+ continue;
+
+ if (warning_at (gimple_location (use_stmt),
+ OPT_Wreturn_local_addr,
+ "function may return address "
+ "of local variable"))
+ inform (DECL_SOURCE_LOCATION(valbase),
+ "declared here");
+
+ if (gimple_bb (use_stmt) == bb)
+ {
+ duplicate = isolate_path (bb, duplicate, e,
+ use_stmt, lhs, true);
+
+ /* When we remove an incoming edge, we need to
+ reprocess the Ith element. */
+ next_i = i;
+ cfg_altered = true;
+ }
+ }
+ }
+ }
+
if (!integer_zerop (op))
continue;
- edge e = gimple_phi_arg_edge (phi, i);
- imm_use_iterator iter;
- gimple use_stmt;
-
/* 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)
{
/* We only care about uses in BB. Catching cases in
in other blocks would require more complex path
- isolation code. */
+ isolation code. */
if (gimple_bb (use_stmt) != bb)
continue;
- if (infer_nonnull_range (use_stmt, lhs))
+ if (infer_nonnull_range (use_stmt, lhs,
+ flag_isolate_erroneous_paths_dereference,
+ flag_isolate_erroneous_paths_attribute))
+
{
- duplicate = isolate_path (bb, duplicate,
- e, use_stmt, lhs);
+ duplicate = isolate_path (bb, duplicate, e,
+ use_stmt, lhs, false);
/* When we remove an incoming edge, we need to
reprocess the Ith element. */
}
}
}
+ }
+}
+
+/* Look for statements which exhibit erroneous behaviour. For example
+ a NULL pointer dereference.
+
+ When found, optimize the block containing the erroneous behaviour. */
+static void
+find_explicit_erroneous_behaviour (void)
+{
+ basic_block bb;
+
+ FOR_EACH_BB_FN (bb, cfun)
+ {
+ gimple_stmt_iterator si;
+
+ /* Out of an abundance of caution, do not isolate paths to a
+ block where the block has any abnormal outgoing edges.
+
+ We might be able to relax this in the future. We have to detect
+ when we have to split the block with the NULL dereference and
+ the trap we insert. We have to preserve abnormal edges out
+ of the isolated block which in turn means updating PHIs at
+ the targets of those abnormal outgoing edges. */
+ if (has_abnormal_or_eh_outgoing_edge_p (bb))
+ continue;
/* Now look at the statements in the block and see if any of
them explicitly dereference a NULL pointer. This happens
/* By passing null_pointer_node, we can use infer_nonnull_range
to detect explicit NULL pointer dereferences and other uses
where a non-NULL value is required. */
- if (infer_nonnull_range (stmt, null_pointer_node))
+ if (infer_nonnull_range (stmt, null_pointer_node,
+ flag_isolate_erroneous_paths_dereference,
+ flag_isolate_erroneous_paths_attribute))
{
insert_trap_and_remove_trailing_statements (&si,
null_pointer_node);
cfg_altered = true;
break;
}
+
+ /* Detect returning the address of a local variable. This only
+ becomes undefined behavior if the result is used, so we do not
+ insert a trap and only return NULL instead. */
+ if (greturn *return_stmt = dyn_cast <greturn *> (stmt))
+ {
+ tree val = gimple_return_retval (return_stmt);
+ if (val && TREE_CODE (val) == ADDR_EXPR)
+ {
+ tree valbase = get_base_address (TREE_OPERAND (val, 0));
+ if ((TREE_CODE (valbase) == VAR_DECL
+ && !is_global_var (valbase))
+ || TREE_CODE (valbase) == PARM_DECL)
+ {
+ /* We only need it for this particular case. */
+ calculate_dominance_info (CDI_POST_DOMINATORS);
+ const char* msg;
+ bool always_executed = dominated_by_p
+ (CDI_POST_DOMINATORS,
+ single_succ (ENTRY_BLOCK_PTR_FOR_FN (cfun)), bb);
+ if (always_executed)
+ msg = N_("function returns address of local variable");
+ else
+ msg = N_("function may return address of "
+ "local variable");
+
+ if (warning_at (gimple_location (stmt),
+ OPT_Wreturn_local_addr, msg))
+ inform (DECL_SOURCE_LOCATION(valbase), "declared here");
+ tree zero = build_zero_cst (TREE_TYPE (val));
+ gimple_return_set_retval (return_stmt, zero);
+ update_stmt (stmt);
+ }
+ }
+ }
}
}
+}
+
+/* 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
+gimple_ssa_isolate_erroneous_paths (void)
+{
+ initialize_original_copy_tables ();
+
+ /* Search all the blocks for edges which, if traversed, will
+ result in undefined behaviour. */
+ cfg_altered = false;
+
+ /* First handle cases where traversal of a particular edge
+ triggers undefined behaviour. These cases require creating
+ duplicate blocks and thus new SSA_NAMEs.
+
+ We want that process complete prior to the phase where we start
+ removing edges from the CFG. Edge removal may ultimately result in
+ removal of PHI nodes and thus releasing SSA_NAMEs back to the
+ name manager.
+
+ If the two processes run in parallel we could release an SSA_NAME
+ back to the manager but we could still have dangling references
+ to the released SSA_NAME in unreachable blocks.
+ that any released names not have dangling references in the IL. */
+ find_implicit_erroneous_behaviour ();
+ find_explicit_erroneous_behaviour ();
+
free_original_copy_tables ();
- /* We scramble the CFG and loop structures a bit, clean up
+ /* 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)
return 0;
}
-static bool
-gate_isolate_erroneous_paths (void)
-{
- /* If we do not have a suitable builtin function for the trap statement,
- then do not perform the optimization. */
- return (flag_isolate_erroneous_paths != 0);
-}
-
namespace {
const pass_data pass_data_isolate_erroneous_paths =
{
GIMPLE_PASS, /* type */
"isolate-paths", /* name */
OPTGROUP_NONE, /* optinfo_flags */
- true, /* has_gate */
- true, /* has_execute */
TV_ISOLATE_ERRONEOUS_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 */
+ 0, /* todo_flags_finish */
};
class pass_isolate_erroneous_paths : public gimple_opt_pass
/* opt_pass methods: */
opt_pass * clone () { return new pass_isolate_erroneous_paths (m_ctxt); }
- bool gate () { return gate_isolate_erroneous_paths (); }
- unsigned int execute () { return gimple_ssa_isolate_erroneous_paths (); }
+ virtual bool gate (function *)
+ {
+ /* If we do not have a suitable builtin function for the trap statement,
+ then do not perform the optimization. */
+ return (flag_isolate_erroneous_paths_dereference != 0
+ || flag_isolate_erroneous_paths_attribute != 0);
+ }
+
+ virtual unsigned int execute (function *)
+ {
+ return gimple_ssa_isolate_erroneous_paths ();
+ }
-}; // class pass_uncprop
+}; // class pass_isolate_erroneous_paths
}
gimple_opt_pass *
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