1061 lines
32 KiB
C
1061 lines
32 KiB
C
/* Forward propagation of expressions for single use variables.
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Copyright (C) 2004, 2005 Free Software Foundation, Inc.
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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
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GCC is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License 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 COPYING. If not, write to
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the Free Software Foundation, 51 Franklin Street, Fifth Floor,
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Boston, MA 02110-1301, USA. */
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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 "tm.h"
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#include "ggc.h"
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#include "tree.h"
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#include "rtl.h"
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#include "tm_p.h"
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#include "basic-block.h"
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#include "timevar.h"
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#include "diagnostic.h"
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#include "tree-flow.h"
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#include "tree-pass.h"
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#include "tree-dump.h"
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#include "langhooks.h"
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/* This pass propagates the RHS of assignment statements into use
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sites of the LHS of the assignment. It's basically a specialized
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form of tree combination. It is hoped all of this can disappear
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when we have a generalized tree combiner.
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Note carefully that after propagation the resulting statement
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must still be a proper gimple statement. Right now we simply
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only perform propagations we know will result in valid gimple
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code. One day we'll want to generalize this code.
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One class of common cases we handle is forward propagating a single use
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variable into a COND_EXPR.
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bb0:
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x = a COND b;
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if (x) goto ... else goto ...
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Will be transformed into:
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bb0:
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if (a COND b) goto ... else goto ...
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Similarly for the tests (x == 0), (x != 0), (x == 1) and (x != 1).
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Or (assuming c1 and c2 are constants):
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bb0:
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x = a + c1;
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if (x EQ/NEQ c2) goto ... else goto ...
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Will be transformed into:
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bb0:
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if (a EQ/NEQ (c2 - c1)) goto ... else goto ...
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Similarly for x = a - c1.
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Or
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bb0:
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x = !a
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if (x) goto ... else goto ...
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Will be transformed into:
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bb0:
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if (a == 0) goto ... else goto ...
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Similarly for the tests (x == 0), (x != 0), (x == 1) and (x != 1).
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For these cases, we propagate A into all, possibly more than one,
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COND_EXPRs that use X.
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Or
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bb0:
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x = (typecast) a
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if (x) goto ... else goto ...
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Will be transformed into:
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bb0:
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if (a != 0) goto ... else goto ...
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(Assuming a is an integral type and x is a boolean or x is an
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integral and a is a boolean.)
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Similarly for the tests (x == 0), (x != 0), (x == 1) and (x != 1).
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For these cases, we propagate A into all, possibly more than one,
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COND_EXPRs that use X.
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In addition to eliminating the variable and the statement which assigns
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a value to the variable, we may be able to later thread the jump without
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adding insane complexity in the dominator optimizer.
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Also note these transformations can cascade. We handle this by having
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a worklist of COND_EXPR statements to examine. As we make a change to
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a statement, we put it back on the worklist to examine on the next
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iteration of the main loop.
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A second class of propagation opportunities arises for ADDR_EXPR
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nodes.
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ptr = &x->y->z;
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res = *ptr;
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Will get turned into
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res = x->y->z;
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Or
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ptr = &x[0];
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ptr2 = ptr + <constant>;
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Will get turned into
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ptr2 = &x[constant/elementsize];
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Or
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ptr = &x[0];
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offset = index * element_size;
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offset_p = (pointer) offset;
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ptr2 = ptr + offset_p
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Will get turned into:
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ptr2 = &x[index];
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We also propagate casts into SWITCH_EXPR and COND_EXPR conditions to
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allow us to remove the cast and {NOT_EXPR,NEG_EXPR} into a subsequent
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{NOT_EXPR,NEG_EXPR}.
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This will (of course) be extended as other needs arise. */
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/* Set to true if we delete EH edges during the optimization. */
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static bool cfg_changed;
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/* Given an SSA_NAME VAR, return true if and only if VAR is defined by
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a comparison. */
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static bool
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ssa_name_defined_by_comparison_p (tree var)
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{
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tree def = SSA_NAME_DEF_STMT (var);
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if (TREE_CODE (def) == MODIFY_EXPR)
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{
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tree rhs = TREE_OPERAND (def, 1);
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return COMPARISON_CLASS_P (rhs);
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}
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return 0;
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}
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/* Forward propagate a single-use variable into COND once. Return a
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new condition if successful. Return NULL_TREE otherwise. */
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static tree
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forward_propagate_into_cond_1 (tree cond, tree *test_var_p)
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{
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tree new_cond = NULL_TREE;
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enum tree_code cond_code = TREE_CODE (cond);
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tree test_var = NULL_TREE;
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tree def;
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tree def_rhs;
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/* If the condition is not a lone variable or an equality test of an
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SSA_NAME against an integral constant, then we do not have an
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optimizable case.
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Note these conditions also ensure the COND_EXPR has no
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virtual operands or other side effects. */
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if (cond_code != SSA_NAME
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&& !((cond_code == EQ_EXPR || cond_code == NE_EXPR)
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&& TREE_CODE (TREE_OPERAND (cond, 0)) == SSA_NAME
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&& CONSTANT_CLASS_P (TREE_OPERAND (cond, 1))
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&& INTEGRAL_TYPE_P (TREE_TYPE (TREE_OPERAND (cond, 1)))))
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return NULL_TREE;
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/* Extract the single variable used in the test into TEST_VAR. */
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if (cond_code == SSA_NAME)
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test_var = cond;
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else
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test_var = TREE_OPERAND (cond, 0);
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/* Now get the defining statement for TEST_VAR. Skip this case if
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it's not defined by some MODIFY_EXPR. */
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def = SSA_NAME_DEF_STMT (test_var);
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if (TREE_CODE (def) != MODIFY_EXPR)
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return NULL_TREE;
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def_rhs = TREE_OPERAND (def, 1);
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/* If TEST_VAR is set by adding or subtracting a constant
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from an SSA_NAME, then it is interesting to us as we
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can adjust the constant in the conditional and thus
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eliminate the arithmetic operation. */
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if (TREE_CODE (def_rhs) == PLUS_EXPR
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|| TREE_CODE (def_rhs) == MINUS_EXPR)
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{
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tree op0 = TREE_OPERAND (def_rhs, 0);
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tree op1 = TREE_OPERAND (def_rhs, 1);
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/* The first operand must be an SSA_NAME and the second
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operand must be a constant. */
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if (TREE_CODE (op0) != SSA_NAME
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|| !CONSTANT_CLASS_P (op1)
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|| !INTEGRAL_TYPE_P (TREE_TYPE (op1)))
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return NULL_TREE;
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/* Don't propagate if the first operand occurs in
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an abnormal PHI. */
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if (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0))
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return NULL_TREE;
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if (has_single_use (test_var))
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{
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enum tree_code new_code;
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tree t;
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/* If the variable was defined via X + C, then we must
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subtract C from the constant in the conditional.
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Otherwise we add C to the constant in the
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conditional. The result must fold into a valid
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gimple operand to be optimizable. */
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new_code = (TREE_CODE (def_rhs) == PLUS_EXPR
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? MINUS_EXPR : PLUS_EXPR);
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t = int_const_binop (new_code, TREE_OPERAND (cond, 1), op1, 0);
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if (!is_gimple_val (t))
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return NULL_TREE;
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new_cond = build2 (cond_code, boolean_type_node, op0, t);
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}
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}
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/* These cases require comparisons of a naked SSA_NAME or
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comparison of an SSA_NAME against zero or one. */
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else if (TREE_CODE (cond) == SSA_NAME
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|| integer_zerop (TREE_OPERAND (cond, 1))
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|| integer_onep (TREE_OPERAND (cond, 1)))
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{
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/* If TEST_VAR is set from a relational operation
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between two SSA_NAMEs or a combination of an SSA_NAME
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and a constant, then it is interesting. */
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if (COMPARISON_CLASS_P (def_rhs))
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{
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tree op0 = TREE_OPERAND (def_rhs, 0);
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tree op1 = TREE_OPERAND (def_rhs, 1);
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/* Both operands of DEF_RHS must be SSA_NAMEs or
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constants. */
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if ((TREE_CODE (op0) != SSA_NAME
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&& !is_gimple_min_invariant (op0))
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|| (TREE_CODE (op1) != SSA_NAME
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&& !is_gimple_min_invariant (op1)))
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return NULL_TREE;
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/* Don't propagate if the first operand occurs in
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an abnormal PHI. */
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if (TREE_CODE (op0) == SSA_NAME
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&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0))
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return NULL_TREE;
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/* Don't propagate if the second operand occurs in
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an abnormal PHI. */
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if (TREE_CODE (op1) == SSA_NAME
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&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op1))
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return NULL_TREE;
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if (has_single_use (test_var))
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{
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/* TEST_VAR was set from a relational operator. */
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new_cond = build2 (TREE_CODE (def_rhs),
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boolean_type_node, op0, op1);
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/* Invert the conditional if necessary. */
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if ((cond_code == EQ_EXPR
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&& integer_zerop (TREE_OPERAND (cond, 1)))
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|| (cond_code == NE_EXPR
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&& integer_onep (TREE_OPERAND (cond, 1))))
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{
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new_cond = invert_truthvalue (new_cond);
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/* If we did not get a simple relational
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expression or bare SSA_NAME, then we can
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not optimize this case. */
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if (!COMPARISON_CLASS_P (new_cond)
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&& TREE_CODE (new_cond) != SSA_NAME)
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new_cond = NULL_TREE;
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}
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}
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}
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/* If TEST_VAR is set from a TRUTH_NOT_EXPR, then it
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is interesting. */
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else if (TREE_CODE (def_rhs) == TRUTH_NOT_EXPR)
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{
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enum tree_code new_code;
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def_rhs = TREE_OPERAND (def_rhs, 0);
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/* DEF_RHS must be an SSA_NAME or constant. */
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if (TREE_CODE (def_rhs) != SSA_NAME
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&& !is_gimple_min_invariant (def_rhs))
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return NULL_TREE;
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/* Don't propagate if the operand occurs in
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an abnormal PHI. */
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if (TREE_CODE (def_rhs) == SSA_NAME
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&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def_rhs))
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return NULL_TREE;
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if (cond_code == SSA_NAME
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|| (cond_code == NE_EXPR
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&& integer_zerop (TREE_OPERAND (cond, 1)))
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|| (cond_code == EQ_EXPR
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&& integer_onep (TREE_OPERAND (cond, 1))))
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new_code = EQ_EXPR;
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else
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new_code = NE_EXPR;
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new_cond = build2 (new_code, boolean_type_node, def_rhs,
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fold_convert (TREE_TYPE (def_rhs),
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integer_zero_node));
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}
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/* If TEST_VAR was set from a cast of an integer type
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to a boolean type or a cast of a boolean to an
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integral, then it is interesting. */
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else if (TREE_CODE (def_rhs) == NOP_EXPR
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|| TREE_CODE (def_rhs) == CONVERT_EXPR)
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{
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tree outer_type;
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tree inner_type;
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outer_type = TREE_TYPE (def_rhs);
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inner_type = TREE_TYPE (TREE_OPERAND (def_rhs, 0));
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if ((TREE_CODE (outer_type) == BOOLEAN_TYPE
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&& INTEGRAL_TYPE_P (inner_type))
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|| (TREE_CODE (inner_type) == BOOLEAN_TYPE
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&& INTEGRAL_TYPE_P (outer_type)))
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;
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else if (INTEGRAL_TYPE_P (outer_type)
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&& INTEGRAL_TYPE_P (inner_type)
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&& TREE_CODE (TREE_OPERAND (def_rhs, 0)) == SSA_NAME
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&& ssa_name_defined_by_comparison_p (TREE_OPERAND (def_rhs,
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0)))
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;
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else
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return NULL_TREE;
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/* Don't propagate if the operand occurs in
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an abnormal PHI. */
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if (TREE_CODE (TREE_OPERAND (def_rhs, 0)) == SSA_NAME
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&& SSA_NAME_OCCURS_IN_ABNORMAL_PHI (TREE_OPERAND
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(def_rhs, 0)))
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return NULL_TREE;
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if (has_single_use (test_var))
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{
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enum tree_code new_code;
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tree new_arg;
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if (cond_code == SSA_NAME
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|| (cond_code == NE_EXPR
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&& integer_zerop (TREE_OPERAND (cond, 1)))
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|| (cond_code == EQ_EXPR
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&& integer_onep (TREE_OPERAND (cond, 1))))
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new_code = NE_EXPR;
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else
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new_code = EQ_EXPR;
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new_arg = TREE_OPERAND (def_rhs, 0);
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new_cond = build2 (new_code, boolean_type_node, new_arg,
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fold_convert (TREE_TYPE (new_arg),
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integer_zero_node));
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}
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}
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}
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*test_var_p = test_var;
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return new_cond;
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}
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/* COND is a condition of the form:
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x == const or x != const
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Look back to x's defining statement and see if x is defined as
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x = (type) y;
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If const is unchanged if we convert it to type, then we can build
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the equivalent expression:
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y == const or y != const
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Which may allow further optimizations.
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Return the equivalent comparison or NULL if no such equivalent comparison
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was found. */
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static tree
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find_equivalent_equality_comparison (tree cond)
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{
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tree op0 = TREE_OPERAND (cond, 0);
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tree op1 = TREE_OPERAND (cond, 1);
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tree def_stmt = SSA_NAME_DEF_STMT (op0);
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while (def_stmt
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&& TREE_CODE (def_stmt) == MODIFY_EXPR
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&& TREE_CODE (TREE_OPERAND (def_stmt, 1)) == SSA_NAME)
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def_stmt = SSA_NAME_DEF_STMT (TREE_OPERAND (def_stmt, 1));
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/* OP0 might have been a parameter, so first make sure it
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was defined by a MODIFY_EXPR. */
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if (def_stmt && TREE_CODE (def_stmt) == MODIFY_EXPR)
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{
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tree def_rhs = TREE_OPERAND (def_stmt, 1);
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/* If either operand to the comparison is a pointer to
|
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a function, then we can not apply this optimization
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as some targets require function pointers to be
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canonicalized and in this case this optimization would
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eliminate a necessary canonicalization. */
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if ((POINTER_TYPE_P (TREE_TYPE (op0))
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&& TREE_CODE (TREE_TYPE (TREE_TYPE (op0))) == FUNCTION_TYPE)
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|| (POINTER_TYPE_P (TREE_TYPE (op1))
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&& TREE_CODE (TREE_TYPE (TREE_TYPE (op1))) == FUNCTION_TYPE))
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return NULL;
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/* Now make sure the RHS of the MODIFY_EXPR is a typecast. */
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if ((TREE_CODE (def_rhs) == NOP_EXPR
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|| TREE_CODE (def_rhs) == CONVERT_EXPR)
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&& TREE_CODE (TREE_OPERAND (def_rhs, 0)) == SSA_NAME)
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{
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tree def_rhs_inner = TREE_OPERAND (def_rhs, 0);
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tree def_rhs_inner_type = TREE_TYPE (def_rhs_inner);
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tree new;
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if (TYPE_PRECISION (def_rhs_inner_type)
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> TYPE_PRECISION (TREE_TYPE (def_rhs)))
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return NULL;
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|
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/* If the inner type of the conversion is a pointer to
|
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a function, then we can not apply this optimization
|
|
as some targets require function pointers to be
|
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canonicalized. This optimization would result in
|
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canonicalization of the pointer when it was not originally
|
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needed/intended. */
|
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if (POINTER_TYPE_P (def_rhs_inner_type)
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&& TREE_CODE (TREE_TYPE (def_rhs_inner_type)) == FUNCTION_TYPE)
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return NULL;
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|
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/* What we want to prove is that if we convert OP1 to
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the type of the object inside the NOP_EXPR that the
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result is still equivalent to SRC.
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If that is true, the build and return new equivalent
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condition which uses the source of the typecast and the
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new constant (which has only changed its type). */
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new = fold_build1 (TREE_CODE (def_rhs), def_rhs_inner_type, op1);
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STRIP_USELESS_TYPE_CONVERSION (new);
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if (is_gimple_val (new) && tree_int_cst_equal (new, op1))
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return build2 (TREE_CODE (cond), TREE_TYPE (cond),
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def_rhs_inner, new);
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}
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}
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return NULL;
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}
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|
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/* STMT is a COND_EXPR
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This routine attempts to find equivalent forms of the condition
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which we may be able to optimize better. */
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|
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static void
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simplify_cond (tree stmt)
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{
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tree cond = COND_EXPR_COND (stmt);
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|
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if (COMPARISON_CLASS_P (cond))
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{
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tree op0 = TREE_OPERAND (cond, 0);
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tree op1 = TREE_OPERAND (cond, 1);
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|
|
if (TREE_CODE (op0) == SSA_NAME && is_gimple_min_invariant (op1))
|
|
{
|
|
/* First see if we have test of an SSA_NAME against a constant
|
|
where the SSA_NAME is defined by an earlier typecast which
|
|
is irrelevant when performing tests against the given
|
|
constant. */
|
|
if (TREE_CODE (cond) == EQ_EXPR || TREE_CODE (cond) == NE_EXPR)
|
|
{
|
|
tree new_cond = find_equivalent_equality_comparison (cond);
|
|
|
|
if (new_cond)
|
|
{
|
|
COND_EXPR_COND (stmt) = new_cond;
|
|
update_stmt (stmt);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Forward propagate a single-use variable into COND_EXPR as many
|
|
times as possible. */
|
|
|
|
static void
|
|
forward_propagate_into_cond (tree cond_expr)
|
|
{
|
|
gcc_assert (TREE_CODE (cond_expr) == COND_EXPR);
|
|
|
|
while (1)
|
|
{
|
|
tree test_var = NULL_TREE;
|
|
tree cond = COND_EXPR_COND (cond_expr);
|
|
tree new_cond = forward_propagate_into_cond_1 (cond, &test_var);
|
|
|
|
/* Return if unsuccessful. */
|
|
if (new_cond == NULL_TREE)
|
|
break;
|
|
|
|
/* Dump details. */
|
|
if (dump_file && (dump_flags & TDF_DETAILS))
|
|
{
|
|
fprintf (dump_file, " Replaced '");
|
|
print_generic_expr (dump_file, cond, dump_flags);
|
|
fprintf (dump_file, "' with '");
|
|
print_generic_expr (dump_file, new_cond, dump_flags);
|
|
fprintf (dump_file, "'\n");
|
|
}
|
|
|
|
COND_EXPR_COND (cond_expr) = new_cond;
|
|
update_stmt (cond_expr);
|
|
|
|
if (has_zero_uses (test_var))
|
|
{
|
|
tree def = SSA_NAME_DEF_STMT (test_var);
|
|
block_stmt_iterator bsi = bsi_for_stmt (def);
|
|
bsi_remove (&bsi, true);
|
|
}
|
|
}
|
|
|
|
/* There are further simplifications that can be performed
|
|
on COND_EXPRs. Specifically, when comparing an SSA_NAME
|
|
against a constant where the SSA_NAME is the result of a
|
|
conversion. Perhaps this should be folded into the rest
|
|
of the COND_EXPR simplification code. */
|
|
simplify_cond (cond_expr);
|
|
}
|
|
|
|
/* We've just substituted an ADDR_EXPR into stmt. Update all the
|
|
relevant data structures to match. */
|
|
|
|
static void
|
|
tidy_after_forward_propagate_addr (tree stmt)
|
|
{
|
|
/* We may have turned a trapping insn into a non-trapping insn. */
|
|
if (maybe_clean_or_replace_eh_stmt (stmt, stmt)
|
|
&& tree_purge_dead_eh_edges (bb_for_stmt (stmt)))
|
|
cfg_changed = true;
|
|
|
|
if (TREE_CODE (TREE_OPERAND (stmt, 1)) == ADDR_EXPR)
|
|
recompute_tree_invariant_for_addr_expr (TREE_OPERAND (stmt, 1));
|
|
|
|
mark_new_vars_to_rename (stmt);
|
|
}
|
|
|
|
/* STMT defines LHS which is contains the address of the 0th element
|
|
in an array. USE_STMT uses LHS to compute the address of an
|
|
arbitrary element within the array. The (variable) byte offset
|
|
of the element is contained in OFFSET.
|
|
|
|
We walk back through the use-def chains of OFFSET to verify that
|
|
it is indeed computing the offset of an element within the array
|
|
and extract the index corresponding to the given byte offset.
|
|
|
|
We then try to fold the entire address expression into a form
|
|
&array[index].
|
|
|
|
If we are successful, we replace the right hand side of USE_STMT
|
|
with the new address computation. */
|
|
|
|
static bool
|
|
forward_propagate_addr_into_variable_array_index (tree offset, tree lhs,
|
|
tree stmt, tree use_stmt)
|
|
{
|
|
tree index;
|
|
|
|
/* The offset must be defined by a simple MODIFY_EXPR statement. */
|
|
if (TREE_CODE (offset) != MODIFY_EXPR)
|
|
return false;
|
|
|
|
/* The RHS of the statement which defines OFFSET must be a gimple
|
|
cast of another SSA_NAME. */
|
|
offset = TREE_OPERAND (offset, 1);
|
|
if (!is_gimple_cast (offset))
|
|
return false;
|
|
|
|
offset = TREE_OPERAND (offset, 0);
|
|
if (TREE_CODE (offset) != SSA_NAME)
|
|
return false;
|
|
|
|
/* Get the defining statement of the offset before type
|
|
conversion. */
|
|
offset = SSA_NAME_DEF_STMT (offset);
|
|
|
|
/* The statement which defines OFFSET before type conversion
|
|
must be a simple MODIFY_EXPR. */
|
|
if (TREE_CODE (offset) != MODIFY_EXPR)
|
|
return false;
|
|
|
|
/* The RHS of the statement which defines OFFSET must be a
|
|
multiplication of an object by the size of the array elements.
|
|
This implicitly verifies that the size of the array elements
|
|
is constant. */
|
|
offset = TREE_OPERAND (offset, 1);
|
|
if (TREE_CODE (offset) != MULT_EXPR
|
|
|| TREE_CODE (TREE_OPERAND (offset, 1)) != INTEGER_CST
|
|
|| !simple_cst_equal (TREE_OPERAND (offset, 1),
|
|
TYPE_SIZE_UNIT (TREE_TYPE (TREE_TYPE (lhs)))))
|
|
return false;
|
|
|
|
/* The first operand to the MULT_EXPR is the desired index. */
|
|
index = TREE_OPERAND (offset, 0);
|
|
|
|
/* Replace the pointer addition with array indexing. */
|
|
TREE_OPERAND (use_stmt, 1) = unshare_expr (TREE_OPERAND (stmt, 1));
|
|
TREE_OPERAND (TREE_OPERAND (TREE_OPERAND (use_stmt, 1), 0), 1) = index;
|
|
|
|
/* That should have created gimple, so there is no need to
|
|
record information to undo the propagation. */
|
|
fold_stmt_inplace (use_stmt);
|
|
tidy_after_forward_propagate_addr (use_stmt);
|
|
return true;
|
|
}
|
|
|
|
/* STMT is a statement of the form SSA_NAME = ADDR_EXPR <whatever>.
|
|
|
|
Try to forward propagate the ADDR_EXPR into the use USE_STMT.
|
|
Often this will allow for removal of an ADDR_EXPR and INDIRECT_REF
|
|
node or for recovery of array indexing from pointer arithmetic.
|
|
|
|
CHANGED is an optional pointer to a boolean variable set to true if
|
|
either the LHS or RHS was changed in the USE_STMT.
|
|
|
|
Return true if the propagation was successful (the propagation can
|
|
be not totally successful, yet things may have been changed). */
|
|
|
|
static bool
|
|
forward_propagate_addr_expr_1 (tree stmt, tree use_stmt, bool *changed)
|
|
{
|
|
tree name = TREE_OPERAND (stmt, 0);
|
|
tree lhs, rhs, array_ref;
|
|
|
|
/* Strip away any outer COMPONENT_REF/ARRAY_REF nodes from the LHS.
|
|
ADDR_EXPR will not appear on the LHS. */
|
|
lhs = TREE_OPERAND (use_stmt, 0);
|
|
while (TREE_CODE (lhs) == COMPONENT_REF || TREE_CODE (lhs) == ARRAY_REF)
|
|
lhs = TREE_OPERAND (lhs, 0);
|
|
|
|
/* Now see if the LHS node is an INDIRECT_REF using NAME. If so,
|
|
propagate the ADDR_EXPR into the use of NAME and fold the result. */
|
|
if (TREE_CODE (lhs) == INDIRECT_REF && TREE_OPERAND (lhs, 0) == name)
|
|
{
|
|
/* This should always succeed in creating gimple, so there is
|
|
no need to save enough state to undo this propagation. */
|
|
TREE_OPERAND (lhs, 0) = unshare_expr (TREE_OPERAND (stmt, 1));
|
|
fold_stmt_inplace (use_stmt);
|
|
tidy_after_forward_propagate_addr (use_stmt);
|
|
if (changed)
|
|
*changed = true;
|
|
}
|
|
|
|
/* Trivial case. The use statement could be a trivial copy. We
|
|
go ahead and handle that case here since it's trivial and
|
|
removes the need to run copy-prop before this pass to get
|
|
the best results. Also note that by handling this case here
|
|
we can catch some cascading effects, ie the single use is
|
|
in a copy, and the copy is used later by a single INDIRECT_REF
|
|
for example. */
|
|
else if (TREE_CODE (lhs) == SSA_NAME && TREE_OPERAND (use_stmt, 1) == name)
|
|
{
|
|
TREE_OPERAND (use_stmt, 1) = unshare_expr (TREE_OPERAND (stmt, 1));
|
|
tidy_after_forward_propagate_addr (use_stmt);
|
|
if (changed)
|
|
*changed = true;
|
|
return true;
|
|
}
|
|
|
|
/* Strip away any outer COMPONENT_REF, ARRAY_REF or ADDR_EXPR
|
|
nodes from the RHS. */
|
|
rhs = TREE_OPERAND (use_stmt, 1);
|
|
while (TREE_CODE (rhs) == COMPONENT_REF
|
|
|| TREE_CODE (rhs) == ARRAY_REF
|
|
|| TREE_CODE (rhs) == ADDR_EXPR)
|
|
rhs = TREE_OPERAND (rhs, 0);
|
|
|
|
/* Now see if the RHS node is an INDIRECT_REF using NAME. If so,
|
|
propagate the ADDR_EXPR into the use of NAME and fold the result. */
|
|
if (TREE_CODE (rhs) == INDIRECT_REF && TREE_OPERAND (rhs, 0) == name)
|
|
{
|
|
/* This should always succeed in creating gimple, so there is
|
|
no need to save enough state to undo this propagation. */
|
|
TREE_OPERAND (rhs, 0) = unshare_expr (TREE_OPERAND (stmt, 1));
|
|
fold_stmt_inplace (use_stmt);
|
|
tidy_after_forward_propagate_addr (use_stmt);
|
|
if (changed)
|
|
*changed = true;
|
|
return true;
|
|
}
|
|
|
|
/* The remaining cases are all for turning pointer arithmetic into
|
|
array indexing. They only apply when we have the address of
|
|
element zero in an array. If that is not the case then there
|
|
is nothing to do. */
|
|
array_ref = TREE_OPERAND (TREE_OPERAND (stmt, 1), 0);
|
|
if (TREE_CODE (array_ref) != ARRAY_REF
|
|
|| TREE_CODE (TREE_TYPE (TREE_OPERAND (array_ref, 0))) != ARRAY_TYPE
|
|
|| !integer_zerop (TREE_OPERAND (array_ref, 1)))
|
|
return false;
|
|
|
|
/* If the use of the ADDR_EXPR must be a PLUS_EXPR, or else there
|
|
is nothing to do. */
|
|
if (TREE_CODE (rhs) != PLUS_EXPR)
|
|
return false;
|
|
|
|
/* Try to optimize &x[0] + C where C is a multiple of the size
|
|
of the elements in X into &x[C/element size]. */
|
|
if (TREE_OPERAND (rhs, 0) == name
|
|
&& TREE_CODE (TREE_OPERAND (rhs, 1)) == INTEGER_CST)
|
|
{
|
|
tree orig = unshare_expr (rhs);
|
|
TREE_OPERAND (rhs, 0) = unshare_expr (TREE_OPERAND (stmt, 1));
|
|
|
|
/* If folding succeeds, then we have just exposed new variables
|
|
in USE_STMT which will need to be renamed. If folding fails,
|
|
then we need to put everything back the way it was. */
|
|
if (fold_stmt_inplace (use_stmt))
|
|
{
|
|
tidy_after_forward_propagate_addr (use_stmt);
|
|
if (changed)
|
|
*changed = true;
|
|
return true;
|
|
}
|
|
else
|
|
{
|
|
TREE_OPERAND (use_stmt, 1) = orig;
|
|
update_stmt (use_stmt);
|
|
return false;
|
|
}
|
|
}
|
|
|
|
/* Try to optimize &x[0] + OFFSET where OFFSET is defined by
|
|
converting a multiplication of an index by the size of the
|
|
array elements, then the result is converted into the proper
|
|
type for the arithmetic. */
|
|
if (TREE_OPERAND (rhs, 0) == name
|
|
&& TREE_CODE (TREE_OPERAND (rhs, 1)) == SSA_NAME
|
|
/* Avoid problems with IVopts creating PLUS_EXPRs with a
|
|
different type than their operands. */
|
|
&& lang_hooks.types_compatible_p (TREE_TYPE (name), TREE_TYPE (rhs)))
|
|
{
|
|
bool res;
|
|
tree offset_stmt = SSA_NAME_DEF_STMT (TREE_OPERAND (rhs, 1));
|
|
|
|
res = forward_propagate_addr_into_variable_array_index (offset_stmt, lhs,
|
|
stmt, use_stmt);
|
|
if (res && changed)
|
|
*changed = true;
|
|
return res;
|
|
}
|
|
|
|
/* Same as the previous case, except the operands of the PLUS_EXPR
|
|
were reversed. */
|
|
if (TREE_OPERAND (rhs, 1) == name
|
|
&& TREE_CODE (TREE_OPERAND (rhs, 0)) == SSA_NAME
|
|
/* Avoid problems with IVopts creating PLUS_EXPRs with a
|
|
different type than their operands. */
|
|
&& lang_hooks.types_compatible_p (TREE_TYPE (name), TREE_TYPE (rhs)))
|
|
{
|
|
bool res;
|
|
tree offset_stmt = SSA_NAME_DEF_STMT (TREE_OPERAND (rhs, 0));
|
|
res = forward_propagate_addr_into_variable_array_index (offset_stmt, lhs,
|
|
stmt, use_stmt);
|
|
if (res && changed)
|
|
*changed = true;
|
|
return res;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/* STMT is a statement of the form SSA_NAME = ADDR_EXPR <whatever>.
|
|
SOME is a pointer to a boolean value indicating whether we
|
|
propagated the address expression anywhere.
|
|
|
|
Try to forward propagate the ADDR_EXPR into all uses of the SSA_NAME.
|
|
Often this will allow for removal of an ADDR_EXPR and INDIRECT_REF
|
|
node or for recovery of array indexing from pointer arithmetic.
|
|
Returns true, if all uses have been propagated into. */
|
|
|
|
static bool
|
|
forward_propagate_addr_expr (tree stmt, bool *some)
|
|
{
|
|
int stmt_loop_depth = bb_for_stmt (stmt)->loop_depth;
|
|
tree name = TREE_OPERAND (stmt, 0);
|
|
imm_use_iterator iter;
|
|
tree use_stmt;
|
|
bool all = true;
|
|
|
|
FOR_EACH_IMM_USE_STMT (use_stmt, iter, name)
|
|
{
|
|
bool result;
|
|
|
|
/* If the use is not in a simple assignment statement, then
|
|
there is nothing we can do. */
|
|
if (TREE_CODE (use_stmt) != MODIFY_EXPR)
|
|
{
|
|
all = false;
|
|
continue;
|
|
}
|
|
|
|
/* If the use is in a deeper loop nest, then we do not want
|
|
to propagate the ADDR_EXPR into the loop as that is likely
|
|
adding expression evaluations into the loop. */
|
|
if (bb_for_stmt (use_stmt)->loop_depth > stmt_loop_depth)
|
|
{
|
|
all = false;
|
|
continue;
|
|
}
|
|
|
|
/* If the use_stmt has side-effects, don't propagate into it. */
|
|
if (stmt_ann (use_stmt)->has_volatile_ops)
|
|
{
|
|
all = false;
|
|
continue;
|
|
}
|
|
|
|
result = forward_propagate_addr_expr_1 (stmt, use_stmt, some);
|
|
*some |= result;
|
|
all &= result;
|
|
}
|
|
|
|
return all;
|
|
}
|
|
|
|
/* If we have lhs = ~x (STMT), look and see if earlier we had x = ~y.
|
|
If so, we can change STMT into lhs = y which can later be copy
|
|
propagated. Similarly for negation.
|
|
|
|
This could trivially be formulated as a forward propagation
|
|
to immediate uses. However, we already had an implementation
|
|
from DOM which used backward propagation via the use-def links.
|
|
|
|
It turns out that backward propagation is actually faster as
|
|
there's less work to do for each NOT/NEG expression we find.
|
|
Backwards propagation needs to look at the statement in a single
|
|
backlink. Forward propagation needs to look at potentially more
|
|
than one forward link. */
|
|
|
|
static void
|
|
simplify_not_neg_expr (tree stmt)
|
|
{
|
|
tree rhs = TREE_OPERAND (stmt, 1);
|
|
tree rhs_def_stmt = SSA_NAME_DEF_STMT (TREE_OPERAND (rhs, 0));
|
|
|
|
/* See if the RHS_DEF_STMT has the same form as our statement. */
|
|
if (TREE_CODE (rhs_def_stmt) == MODIFY_EXPR
|
|
&& TREE_CODE (TREE_OPERAND (rhs_def_stmt, 1)) == TREE_CODE (rhs))
|
|
{
|
|
tree rhs_def_operand = TREE_OPERAND (TREE_OPERAND (rhs_def_stmt, 1), 0);
|
|
|
|
/* Verify that RHS_DEF_OPERAND is a suitable SSA_NAME. */
|
|
if (TREE_CODE (rhs_def_operand) == SSA_NAME
|
|
&& ! SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rhs_def_operand))
|
|
{
|
|
TREE_OPERAND (stmt, 1) = rhs_def_operand;
|
|
update_stmt (stmt);
|
|
}
|
|
}
|
|
}
|
|
|
|
/* STMT is a SWITCH_EXPR for which we attempt to find equivalent forms of
|
|
the condition which we may be able to optimize better. */
|
|
|
|
static void
|
|
simplify_switch_expr (tree stmt)
|
|
{
|
|
tree cond = SWITCH_COND (stmt);
|
|
tree def, to, ti;
|
|
|
|
/* The optimization that we really care about is removing unnecessary
|
|
casts. That will let us do much better in propagating the inferred
|
|
constant at the switch target. */
|
|
if (TREE_CODE (cond) == SSA_NAME)
|
|
{
|
|
def = SSA_NAME_DEF_STMT (cond);
|
|
if (TREE_CODE (def) == MODIFY_EXPR)
|
|
{
|
|
def = TREE_OPERAND (def, 1);
|
|
if (TREE_CODE (def) == NOP_EXPR)
|
|
{
|
|
int need_precision;
|
|
bool fail;
|
|
|
|
def = TREE_OPERAND (def, 0);
|
|
|
|
#ifdef ENABLE_CHECKING
|
|
/* ??? Why was Jeff testing this? We are gimple... */
|
|
gcc_assert (is_gimple_val (def));
|
|
#endif
|
|
|
|
to = TREE_TYPE (cond);
|
|
ti = TREE_TYPE (def);
|
|
|
|
/* If we have an extension that preserves value, then we
|
|
can copy the source value into the switch. */
|
|
|
|
need_precision = TYPE_PRECISION (ti);
|
|
fail = false;
|
|
if (! INTEGRAL_TYPE_P (ti))
|
|
fail = true;
|
|
else if (TYPE_UNSIGNED (to) && !TYPE_UNSIGNED (ti))
|
|
fail = true;
|
|
else if (!TYPE_UNSIGNED (to) && TYPE_UNSIGNED (ti))
|
|
need_precision += 1;
|
|
if (TYPE_PRECISION (to) < need_precision)
|
|
fail = true;
|
|
|
|
if (!fail)
|
|
{
|
|
SWITCH_COND (stmt) = def;
|
|
update_stmt (stmt);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Main entry point for the forward propagation optimizer. */
|
|
|
|
static unsigned int
|
|
tree_ssa_forward_propagate_single_use_vars (void)
|
|
{
|
|
basic_block bb;
|
|
unsigned int todoflags = 0;
|
|
|
|
cfg_changed = false;
|
|
|
|
FOR_EACH_BB (bb)
|
|
{
|
|
block_stmt_iterator bsi;
|
|
|
|
/* Note we update BSI within the loop as necessary. */
|
|
for (bsi = bsi_start (bb); !bsi_end_p (bsi); )
|
|
{
|
|
tree stmt = bsi_stmt (bsi);
|
|
|
|
/* If this statement sets an SSA_NAME to an address,
|
|
try to propagate the address into the uses of the SSA_NAME. */
|
|
if (TREE_CODE (stmt) == MODIFY_EXPR)
|
|
{
|
|
tree lhs = TREE_OPERAND (stmt, 0);
|
|
tree rhs = TREE_OPERAND (stmt, 1);
|
|
|
|
|
|
if (TREE_CODE (lhs) != SSA_NAME)
|
|
{
|
|
bsi_next (&bsi);
|
|
continue;
|
|
}
|
|
|
|
if (TREE_CODE (rhs) == ADDR_EXPR)
|
|
{
|
|
bool some = false;
|
|
if (forward_propagate_addr_expr (stmt, &some))
|
|
bsi_remove (&bsi, true);
|
|
else
|
|
bsi_next (&bsi);
|
|
if (some)
|
|
todoflags |= TODO_update_smt_usage;
|
|
}
|
|
else if ((TREE_CODE (rhs) == BIT_NOT_EXPR
|
|
|| TREE_CODE (rhs) == NEGATE_EXPR)
|
|
&& TREE_CODE (TREE_OPERAND (rhs, 0)) == SSA_NAME)
|
|
{
|
|
simplify_not_neg_expr (stmt);
|
|
bsi_next (&bsi);
|
|
}
|
|
else
|
|
bsi_next (&bsi);
|
|
}
|
|
else if (TREE_CODE (stmt) == SWITCH_EXPR)
|
|
{
|
|
simplify_switch_expr (stmt);
|
|
bsi_next (&bsi);
|
|
}
|
|
else if (TREE_CODE (stmt) == COND_EXPR)
|
|
{
|
|
forward_propagate_into_cond (stmt);
|
|
bsi_next (&bsi);
|
|
}
|
|
else
|
|
bsi_next (&bsi);
|
|
}
|
|
}
|
|
|
|
if (cfg_changed)
|
|
cleanup_tree_cfg ();
|
|
return todoflags;
|
|
}
|
|
|
|
|
|
static bool
|
|
gate_forwprop (void)
|
|
{
|
|
return 1;
|
|
}
|
|
|
|
struct tree_opt_pass pass_forwprop = {
|
|
"forwprop", /* name */
|
|
gate_forwprop, /* gate */
|
|
tree_ssa_forward_propagate_single_use_vars, /* execute */
|
|
NULL, /* sub */
|
|
NULL, /* next */
|
|
0, /* static_pass_number */
|
|
TV_TREE_FORWPROP, /* tv_id */
|
|
PROP_cfg | PROP_ssa
|
|
| PROP_alias, /* properties_required */
|
|
0, /* properties_provided */
|
|
PROP_smt_usage, /* properties_destroyed */
|
|
0, /* todo_flags_start */
|
|
TODO_dump_func /* todo_flags_finish */
|
|
| TODO_ggc_collect
|
|
| TODO_update_ssa | TODO_verify_ssa,
|
|
0 /* letter */
|
|
};
|