525 lines
16 KiB
C
525 lines
16 KiB
C
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/* Warn on problematic uses of alloca and variable length arrays.
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Copyright (C) 2016 Free Software Foundation, Inc.
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Contributed by Aldy Hernandez <aldyh@redhat.com>.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 3, or (at your option) any later
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version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3. If not see
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<http://www.gnu.org/licenses/>. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "backend.h"
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#include "tree.h"
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#include "gimple.h"
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#include "tree-pass.h"
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#include "ssa.h"
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#include "gimple-pretty-print.h"
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#include "diagnostic-core.h"
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#include "fold-const.h"
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#include "gimple-iterator.h"
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#include "tree-ssa.h"
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#include "params.h"
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#include "tree-cfg.h"
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#include "calls.h"
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#include "cfgloop.h"
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#include "intl.h"
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const pass_data pass_data_walloca = {
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GIMPLE_PASS,
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"walloca",
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OPTGROUP_NONE,
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TV_NONE,
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PROP_cfg, // properties_required
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0, // properties_provided
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0, // properties_destroyed
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0, // properties_start
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0, // properties_finish
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};
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class pass_walloca : public gimple_opt_pass
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{
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public:
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pass_walloca (gcc::context *ctxt)
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: gimple_opt_pass(pass_data_walloca, ctxt), first_time_p (false)
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{}
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opt_pass *clone () { return new pass_walloca (m_ctxt); }
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void set_pass_param (unsigned int n, bool param)
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{
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gcc_assert (n == 0);
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first_time_p = param;
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}
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virtual bool gate (function *);
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virtual unsigned int execute (function *);
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private:
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// Set to TRUE the first time we run this pass on a function.
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bool first_time_p;
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};
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bool
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pass_walloca::gate (function *fun ATTRIBUTE_UNUSED)
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{
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// The first time this pass is called, it is called before
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// optimizations have been run and range information is unavailable,
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// so we can only perform strict alloca checking.
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if (first_time_p)
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return warn_alloca != 0;
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return warn_alloca_limit > 0 || warn_vla_limit > 0;
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}
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// Possible problematic uses of alloca.
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enum alloca_type {
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// Alloca argument is within known bounds that are appropriate.
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ALLOCA_OK,
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// Alloca argument is KNOWN to have a value that is too large.
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ALLOCA_BOUND_DEFINITELY_LARGE,
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// Alloca argument may be too large.
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ALLOCA_BOUND_MAYBE_LARGE,
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// Alloca argument is bounded but of an indeterminate size.
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ALLOCA_BOUND_UNKNOWN,
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// Alloca argument was casted from a signed integer.
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ALLOCA_CAST_FROM_SIGNED,
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// Alloca appears in a loop.
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ALLOCA_IN_LOOP,
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// Alloca argument is 0.
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ALLOCA_ARG_IS_ZERO,
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// Alloca call is unbounded. That is, there is no controlling
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// predicate for its argument.
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ALLOCA_UNBOUNDED
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};
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// Type of an alloca call with its corresponding limit, if applicable.
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struct alloca_type_and_limit {
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enum alloca_type type;
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// For ALLOCA_BOUND_MAYBE_LARGE and ALLOCA_BOUND_DEFINITELY_LARGE
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// types, this field indicates the assumed limit if known or
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// integer_zero_node if unknown. For any other alloca types, this
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// field is undefined.
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wide_int limit;
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alloca_type_and_limit ();
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alloca_type_and_limit (enum alloca_type type,
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wide_int i) : type(type), limit(i) { }
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alloca_type_and_limit (enum alloca_type type) : type(type) { }
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};
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// NOTE: When we get better range info, this entire function becomes
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// irrelevant, as it should be possible to get range info for an SSA
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// name at any point in the program.
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//
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// We have a few heuristics up our sleeve to determine if a call to
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// alloca() is within bounds. Try them out and return the type of
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// alloca call with its assumed limit (if applicable).
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//
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// Given a known argument (ARG) to alloca() and an EDGE (E)
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// calculating said argument, verify that the last statement in the BB
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// in E->SRC is a gate comparing ARG to an acceptable bound for
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// alloca(). See examples below.
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//
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// If set, ARG_CASTED is the possible unsigned argument to which ARG
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// was casted to. This is to handle cases where the controlling
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// predicate is looking at a casted value, not the argument itself.
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// arg_casted = (size_t) arg;
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// if (arg_casted < N)
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// goto bb3;
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// else
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// goto bb5;
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//
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// MAX_SIZE is WARN_ALLOCA= adjusted for VLAs. It is the maximum size
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// in bytes we allow for arg.
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static struct alloca_type_and_limit
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alloca_call_type_by_arg (tree arg, tree arg_casted, edge e, unsigned max_size)
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{
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basic_block bb = e->src;
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gimple_stmt_iterator gsi = gsi_last_bb (bb);
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gimple *last = gsi_stmt (gsi);
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if (!last || gimple_code (last) != GIMPLE_COND)
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return alloca_type_and_limit (ALLOCA_UNBOUNDED);
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enum tree_code cond_code = gimple_cond_code (last);
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if (e->flags & EDGE_TRUE_VALUE)
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;
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else if (e->flags & EDGE_FALSE_VALUE)
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cond_code = invert_tree_comparison (cond_code, false);
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else
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return alloca_type_and_limit (ALLOCA_UNBOUNDED);
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// Check for:
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// if (ARG .COND. N)
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// goto <bb 3>;
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// else
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// goto <bb 4>;
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// <bb 3>:
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// alloca(ARG);
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if ((cond_code == LE_EXPR
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|| cond_code == LT_EXPR
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|| cond_code == GT_EXPR
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|| cond_code == GE_EXPR)
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&& (gimple_cond_lhs (last) == arg
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|| gimple_cond_lhs (last) == arg_casted))
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{
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if (TREE_CODE (gimple_cond_rhs (last)) == INTEGER_CST)
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{
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tree rhs = gimple_cond_rhs (last);
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int tst = wi::cmpu (wi::to_widest (rhs), max_size);
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if ((cond_code == LT_EXPR && tst == -1)
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|| (cond_code == LE_EXPR && (tst == -1 || tst == 0)))
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return alloca_type_and_limit (ALLOCA_OK);
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else
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{
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// Let's not get too specific as to how large the limit
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// may be. Someone's clearly an idiot when things
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// degrade into "if (N > Y) alloca(N)".
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if (cond_code == GT_EXPR || cond_code == GE_EXPR)
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rhs = integer_zero_node;
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return alloca_type_and_limit (ALLOCA_BOUND_MAYBE_LARGE, rhs);
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}
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}
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else
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return alloca_type_and_limit (ALLOCA_BOUND_UNKNOWN);
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}
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// Similarly, but check for a comparison with an unknown LIMIT.
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// if (LIMIT .COND. ARG)
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// alloca(arg);
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//
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// Where LIMIT has a bound of unknown range.
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//
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// Note: All conditions of the form (ARG .COND. XXXX) where covered
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// by the previous check above, so we only need to look for (LIMIT
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// .COND. ARG) here.
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tree limit = gimple_cond_lhs (last);
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if ((gimple_cond_rhs (last) == arg
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|| gimple_cond_rhs (last) == arg_casted)
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&& TREE_CODE (limit) == SSA_NAME)
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{
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wide_int min, max;
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value_range_type range_type = get_range_info (limit, &min, &max);
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if (range_type == VR_UNDEFINED || range_type == VR_VARYING)
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return alloca_type_and_limit (ALLOCA_BOUND_UNKNOWN);
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// ?? It looks like the above `if' is unnecessary, as we never
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// get any VR_RANGE or VR_ANTI_RANGE here. If we had a range
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// for LIMIT, I suppose we would have taken care of it in
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// alloca_call_type(), or handled above where we handle (ARG .COND. N).
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//
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// If this ever triggers, we should probably figure out why and
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// handle it, though it is likely to be just an ALLOCA_UNBOUNDED.
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return alloca_type_and_limit (ALLOCA_UNBOUNDED);
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}
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return alloca_type_and_limit (ALLOCA_UNBOUNDED);
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}
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// Return TRUE if SSA's definition is a cast from a signed type.
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// If so, set *INVALID_CASTED_TYPE to the signed type.
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static bool
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cast_from_signed_p (tree ssa, tree *invalid_casted_type)
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{
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gimple *def = SSA_NAME_DEF_STMT (ssa);
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if (def
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&& !gimple_nop_p (def)
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&& gimple_assign_cast_p (def)
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&& !TYPE_UNSIGNED (TREE_TYPE (gimple_assign_rhs1 (def))))
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{
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*invalid_casted_type = TREE_TYPE (gimple_assign_rhs1 (def));
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return true;
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}
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return false;
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}
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// Return TRUE if X has a maximum range of MAX, basically covering the
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// entire domain, in which case it's no range at all.
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static bool
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is_max (tree x, wide_int max)
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{
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return wi::max_value (TREE_TYPE (x)) == max;
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}
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// Analyze the alloca call in STMT and return the alloca type with its
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// corresponding limit (if applicable). IS_VLA is set if the alloca
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// call is really a BUILT_IN_ALLOCA_WITH_ALIGN, signifying a VLA.
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//
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// If the alloca call may be too large because of a cast from a signed
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// type to an unsigned type, set *INVALID_CASTED_TYPE to the
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// problematic signed type.
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static struct alloca_type_and_limit
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alloca_call_type (gimple *stmt, bool is_vla, tree *invalid_casted_type)
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{
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gcc_assert (gimple_alloca_call_p (stmt));
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tree len = gimple_call_arg (stmt, 0);
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tree len_casted = NULL;
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wide_int min, max;
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struct alloca_type_and_limit ret = alloca_type_and_limit (ALLOCA_UNBOUNDED);
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gcc_assert (!is_vla || warn_vla_limit > 0);
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gcc_assert (is_vla || warn_alloca_limit > 0);
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// Adjust warn_alloca_max_size for VLAs, by taking the underlying
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// type into account.
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unsigned HOST_WIDE_INT max_size;
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if (is_vla)
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max_size = (unsigned HOST_WIDE_INT) warn_vla_limit;
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else
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max_size = (unsigned HOST_WIDE_INT) warn_alloca_limit;
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// Check for the obviously bounded case.
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if (TREE_CODE (len) == INTEGER_CST)
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{
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if (tree_to_uhwi (len) > max_size)
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return alloca_type_and_limit (ALLOCA_BOUND_DEFINITELY_LARGE, len);
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if (integer_zerop (len))
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return alloca_type_and_limit (ALLOCA_ARG_IS_ZERO);
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ret = alloca_type_and_limit (ALLOCA_OK);
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}
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// Check the range info if available.
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else if (value_range_type range_type = get_range_info (len, &min, &max))
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{
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if (range_type == VR_RANGE)
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{
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if (wi::leu_p (max, max_size))
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ret = alloca_type_and_limit (ALLOCA_OK);
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else
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{
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// A cast may have created a range we don't care
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// about. For instance, a cast from 16-bit to
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// 32-bit creates a range of 0..65535, even if there
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// is not really a determinable range in the
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// underlying code. In this case, look through the
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// cast at the original argument, and fall through
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// to look at other alternatives.
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//
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// We only look at through the cast when its from
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// unsigned to unsigned, otherwise we may risk
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// looking at SIGNED_INT < N, which is clearly not
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// what we want. In this case, we'd be interested
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// in a VR_RANGE of [0..N].
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//
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// Note: None of this is perfect, and should all go
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// away with better range information. But it gets
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// most of the cases.
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gimple *def = SSA_NAME_DEF_STMT (len);
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if (gimple_assign_cast_p (def)
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&& TYPE_UNSIGNED (TREE_TYPE (gimple_assign_rhs1 (def))))
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{
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len_casted = gimple_assign_rhs1 (def);
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range_type = get_range_info (len_casted, &min, &max);
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}
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// An unknown range or a range of the entire domain is
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// really no range at all.
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if (range_type == VR_VARYING
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|| (!len_casted && is_max (len, max))
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|| (len_casted && is_max (len_casted, max)))
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{
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// Fall through.
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}
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else if (range_type != VR_VARYING)
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return
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alloca_type_and_limit (ALLOCA_BOUND_MAYBE_LARGE, max);
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}
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}
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else if (range_type == VR_ANTI_RANGE)
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{
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// There may be some wrapping around going on. Catch it
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// with this heuristic. Hopefully, this VR_ANTI_RANGE
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// nonsense will go away, and we won't have to catch the
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// sign conversion problems with this crap.
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if (cast_from_signed_p (len, invalid_casted_type))
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return alloca_type_and_limit (ALLOCA_CAST_FROM_SIGNED);
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}
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// No easily determined range and try other things.
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}
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// If we couldn't find anything, try a few heuristics for things we
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// can easily determine. Check these misc cases but only accept
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// them if all predecessors have a known bound.
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basic_block bb = gimple_bb (stmt);
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if (ret.type == ALLOCA_UNBOUNDED)
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{
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ret.type = ALLOCA_OK;
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for (unsigned ix = 0; ix < EDGE_COUNT (bb->preds); ix++)
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{
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gcc_assert (!len_casted || TYPE_UNSIGNED (TREE_TYPE (len_casted)));
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ret = alloca_call_type_by_arg (len, len_casted,
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EDGE_PRED (bb, ix), max_size);
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if (ret.type != ALLOCA_OK)
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return ret;
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}
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}
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return ret;
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}
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// Return TRUE if the alloca call in STMT is in a loop, otherwise
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// return FALSE. As an exception, ignore alloca calls for VLAs that
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// occur in a loop since those will be cleaned up when they go out of
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// scope.
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static bool
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in_loop_p (bool is_vla, gimple *stmt)
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{
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basic_block bb = gimple_bb (stmt);
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if (bb->loop_father
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&& bb->loop_father->header != ENTRY_BLOCK_PTR_FOR_FN (cfun))
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{
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// Do not warn on VLAs occurring in a loop, since VLAs are
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// guaranteed to be cleaned up when they go out of scope.
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// That is, there is a corresponding __builtin_stack_restore
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// at the end of the scope in which the VLA occurs.
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tree fndecl = gimple_call_fn (stmt);
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while (TREE_CODE (fndecl) == ADDR_EXPR)
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fndecl = TREE_OPERAND (fndecl, 0);
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if (DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL
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&& is_vla
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&& DECL_FUNCTION_CODE (fndecl) == BUILT_IN_ALLOCA_WITH_ALIGN)
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return false;
|
||
|
|
||
|
return true;
|
||
|
}
|
||
|
return false;
|
||
|
}
|
||
|
|
||
|
unsigned int
|
||
|
pass_walloca::execute (function *fun)
|
||
|
{
|
||
|
basic_block bb;
|
||
|
FOR_EACH_BB_FN (bb, fun)
|
||
|
{
|
||
|
for (gimple_stmt_iterator si = gsi_start_bb (bb); !gsi_end_p (si);
|
||
|
gsi_next (&si))
|
||
|
{
|
||
|
gimple *stmt = gsi_stmt (si);
|
||
|
location_t loc = gimple_location (stmt);
|
||
|
|
||
|
if (!gimple_alloca_call_p (stmt))
|
||
|
continue;
|
||
|
gcc_assert (gimple_call_num_args (stmt) >= 1);
|
||
|
|
||
|
bool is_vla = gimple_alloca_call_p (stmt)
|
||
|
&& gimple_call_alloca_for_var_p (as_a <gcall *> (stmt));
|
||
|
|
||
|
// Strict mode whining for VLAs is handled by the front-end,
|
||
|
// so we can safely ignore this case. Also, ignore VLAs if
|
||
|
// the user doesn't care about them.
|
||
|
if (is_vla
|
||
|
&& (warn_vla > 0 || !warn_vla_limit))
|
||
|
continue;
|
||
|
|
||
|
if (!is_vla && (warn_alloca || !warn_alloca_limit))
|
||
|
{
|
||
|
if (warn_alloca)
|
||
|
warning_at (loc, OPT_Walloca, G_("use of %<alloca%>"));
|
||
|
continue;
|
||
|
}
|
||
|
|
||
|
tree invalid_casted_type = NULL;
|
||
|
struct alloca_type_and_limit t
|
||
|
= alloca_call_type (stmt, is_vla, &invalid_casted_type);
|
||
|
|
||
|
// Even if we think the alloca call is OK, make sure it's
|
||
|
// not in a loop.
|
||
|
if (t.type == ALLOCA_OK && in_loop_p (is_vla, stmt))
|
||
|
t = alloca_type_and_limit (ALLOCA_IN_LOOP);
|
||
|
|
||
|
enum opt_code wcode
|
||
|
= is_vla ? OPT_Wvla_larger_than_ : OPT_Walloca_larger_than_;
|
||
|
char buff[WIDE_INT_MAX_PRECISION / 4 + 4];
|
||
|
switch (t.type)
|
||
|
{
|
||
|
case ALLOCA_OK:
|
||
|
break;
|
||
|
case ALLOCA_BOUND_MAYBE_LARGE:
|
||
|
if (warning_at (loc, wcode,
|
||
|
is_vla ? G_("argument to variable-length array "
|
||
|
"may be too large")
|
||
|
: G_("argument to %<alloca%> may be too large"))
|
||
|
&& t.limit != integer_zero_node)
|
||
|
{
|
||
|
print_decu (t.limit, buff);
|
||
|
inform (loc, G_("limit is %u bytes, but argument "
|
||
|
"may be as large as %s"),
|
||
|
is_vla ? warn_vla_limit : warn_alloca_limit, buff);
|
||
|
}
|
||
|
break;
|
||
|
case ALLOCA_BOUND_DEFINITELY_LARGE:
|
||
|
if (warning_at (loc, wcode,
|
||
|
is_vla ? G_("argument to variable-length array "
|
||
|
"is too large")
|
||
|
: G_("argument to %<alloca%> is too large"))
|
||
|
&& t.limit != integer_zero_node)
|
||
|
{
|
||
|
print_decu (t.limit, buff);
|
||
|
inform (loc, G_("limit is %u bytes, but argument is %s"),
|
||
|
is_vla ? warn_vla_limit : warn_alloca_limit, buff);
|
||
|
}
|
||
|
break;
|
||
|
case ALLOCA_BOUND_UNKNOWN:
|
||
|
warning_at (loc, wcode,
|
||
|
is_vla ? G_("variable-length array bound is unknown")
|
||
|
: G_("%<alloca%> bound is unknown"));
|
||
|
break;
|
||
|
case ALLOCA_UNBOUNDED:
|
||
|
warning_at (loc, wcode,
|
||
|
is_vla ? G_("unbounded use of variable-length array")
|
||
|
: G_("unbounded use of %<alloca%>"));
|
||
|
break;
|
||
|
case ALLOCA_IN_LOOP:
|
||
|
gcc_assert (!is_vla);
|
||
|
warning_at (loc, wcode, G_("use of %<alloca%> within a loop"));
|
||
|
break;
|
||
|
case ALLOCA_CAST_FROM_SIGNED:
|
||
|
gcc_assert (invalid_casted_type != NULL_TREE);
|
||
|
warning_at (loc, wcode,
|
||
|
is_vla ? G_("argument to variable-length array "
|
||
|
"may be too large due to "
|
||
|
"conversion from %qT to %qT")
|
||
|
: G_("argument to %<alloca%> may be too large "
|
||
|
"due to conversion from %qT to %qT"),
|
||
|
invalid_casted_type, size_type_node);
|
||
|
break;
|
||
|
case ALLOCA_ARG_IS_ZERO:
|
||
|
warning_at (loc, wcode,
|
||
|
is_vla ? G_("argument to variable-length array "
|
||
|
"is zero")
|
||
|
: G_("argument to %<alloca%> is zero"));
|
||
|
break;
|
||
|
default:
|
||
|
gcc_unreachable ();
|
||
|
}
|
||
|
}
|
||
|
}
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
|
gimple_opt_pass *
|
||
|
make_pass_walloca (gcc::context *ctxt)
|
||
|
{
|
||
|
return new pass_walloca (ctxt);
|
||
|
}
|