/* This pass propagates the RHS of assignment statements into use
sites of the LHS of the assignment. It's basically a specialized
- form of tree combination.
+ form of tree combination. It is hoped all of this can disappear
+ when we have a generalized tree combiner.
Note carefully that after propagation the resulting statement
must still be a proper gimple statement. Right now we simply
ptr2 = &x[index];
+ We also propagate casts into SWITCH_EXPR and COND_EXPR conditions to
+ allow us to remove the cast and {NOT_EXPR,NEG_EXPR} into a subsequent
+ {NOT_EXPR,NEG_EXPR}.
This will (of course) be extended as other needs arise. */
return new_cond;
}
+/* COND is a condition of the form:
+
+ x == const or x != const
+
+ Look back to x's defining statement and see if x is defined as
+
+ x = (type) y;
+
+ If const is unchanged if we convert it to type, then we can build
+ the equivalent expression:
+
+
+ y == const or y != const
+
+ Which may allow further optimizations.
+
+ Return the equivalent comparison or NULL if no such equivalent comparison
+ was found. */
+
+static tree
+find_equivalent_equality_comparison (tree cond)
+{
+ tree op0 = TREE_OPERAND (cond, 0);
+ tree op1 = TREE_OPERAND (cond, 1);
+ tree def_stmt = SSA_NAME_DEF_STMT (op0);
+
+ while (def_stmt
+ && TREE_CODE (def_stmt) == MODIFY_EXPR
+ && TREE_CODE (TREE_OPERAND (def_stmt, 1)) == SSA_NAME)
+ def_stmt = SSA_NAME_DEF_STMT (TREE_OPERAND (def_stmt, 1));
+
+ /* OP0 might have been a parameter, so first make sure it
+ was defined by a MODIFY_EXPR. */
+ if (def_stmt && TREE_CODE (def_stmt) == MODIFY_EXPR)
+ {
+ tree def_rhs = TREE_OPERAND (def_stmt, 1);
+
+ /* If either operand to the comparison is a pointer to
+ a function, then we can not apply this optimization
+ as some targets require function pointers to be
+ canonicalized and in this case this optimization would
+ eliminate a necessary canonicalization. */
+ if ((POINTER_TYPE_P (TREE_TYPE (op0))
+ && TREE_CODE (TREE_TYPE (TREE_TYPE (op0))) == FUNCTION_TYPE)
+ || (POINTER_TYPE_P (TREE_TYPE (op1))
+ && TREE_CODE (TREE_TYPE (TREE_TYPE (op1))) == FUNCTION_TYPE))
+ return NULL;
+
+ /* Now make sure the RHS of the MODIFY_EXPR is a typecast. */
+ if ((TREE_CODE (def_rhs) == NOP_EXPR
+ || TREE_CODE (def_rhs) == CONVERT_EXPR)
+ && TREE_CODE (TREE_OPERAND (def_rhs, 0)) == SSA_NAME)
+ {
+ tree def_rhs_inner = TREE_OPERAND (def_rhs, 0);
+ tree def_rhs_inner_type = TREE_TYPE (def_rhs_inner);
+ tree new;
+
+ if (TYPE_PRECISION (def_rhs_inner_type)
+ > TYPE_PRECISION (TREE_TYPE (def_rhs)))
+ return NULL;
+
+ /* If the inner type of the conversion is a pointer to
+ a function, then we can not apply this optimization
+ as some targets require function pointers to be
+ canonicalized. This optimization would result in
+ canonicalization of the pointer when it was not originally
+ needed/intended. */
+ if (POINTER_TYPE_P (def_rhs_inner_type)
+ && TREE_CODE (TREE_TYPE (def_rhs_inner_type)) == FUNCTION_TYPE)
+ return NULL;
+
+ /* What we want to prove is that if we convert OP1 to
+ the type of the object inside the NOP_EXPR that the
+ result is still equivalent to SRC.
+
+ If that is true, the build and return new equivalent
+ condition which uses the source of the typecast and the
+ new constant (which has only changed its type). */
+ new = fold_build1 (TREE_CODE (def_rhs), def_rhs_inner_type, op1);
+ STRIP_USELESS_TYPE_CONVERSION (new);
+ if (is_gimple_val (new) && tree_int_cst_equal (new, op1))
+ return build2 (TREE_CODE (cond), TREE_TYPE (cond),
+ def_rhs_inner, new);
+ }
+ }
+ return NULL;
+}
+
+/* STMT is a COND_EXPR
+
+ This routine attempts to find equivalent forms of the condition
+ which we may be able to optimize better. */
+
+static void
+simplify_cond (tree stmt)
+{
+ tree cond = COND_EXPR_COND (stmt);
+
+ if (COMPARISON_CLASS_P (cond))
+ {
+ tree op0 = TREE_OPERAND (cond, 0);
+ tree op1 = TREE_OPERAND (cond, 1);
+
+ 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. */
{
tree def = SSA_NAME_DEF_STMT (test_var);
block_stmt_iterator bsi = bsi_for_stmt (def);
- bsi_remove (&bsi);
+ 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
static void
tidy_after_forward_propagate_addr (tree stmt)
{
- mark_new_vars_to_rename (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_invarant_for_addr_expr (TREE_OPERAND (stmt, 1));
+ recompute_tree_invariant_for_addr_expr (TREE_OPERAND (stmt, 1));
- update_stmt (stmt);
+ mark_new_vars_to_rename (stmt);
}
/* STMT defines LHS which is contains the address of the 0th element
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.
- Return true, if the propagation was successful. */
+
+ 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)
+forward_propagate_addr_expr_1 (tree stmt, tree use_stmt, bool *changed)
{
tree name = TREE_OPERAND (stmt, 0);
tree lhs, rhs, array_ref;
TREE_OPERAND (lhs, 0) = unshare_expr (TREE_OPERAND (stmt, 1));
fold_stmt_inplace (use_stmt);
tidy_after_forward_propagate_addr (use_stmt);
- return true;
+ if (changed)
+ *changed = true;
}
/* Trivial case. The use statement could be a trivial copy. We
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. */
- if (TREE_CODE (lhs) == SSA_NAME && TREE_OPERAND (use_stmt, 1) == name)
+ 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;
}
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;
}
if (fold_stmt_inplace (use_stmt))
{
tidy_after_forward_propagate_addr (use_stmt);
+ if (changed)
+ *changed = true;
return true;
}
else
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));
- return forward_propagate_addr_into_variable_array_index (offset_stmt, lhs,
- stmt, use_stmt);
+
+ 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
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));
- return forward_propagate_addr_into_variable_array_index (offset_stmt, lhs,
- stmt, use_stmt);
+ 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
Returns true, if all uses have been propagated into. */
static bool
-forward_propagate_addr_expr (tree stmt)
+forward_propagate_addr_expr (tree stmt, bool *some)
{
int stmt_loop_depth = bb_for_stmt (stmt)->loop_depth;
tree name = TREE_OPERAND (stmt, 0);
- use_operand_p imm_use;
imm_use_iterator iter;
+ tree use_stmt;
bool all = true;
- FOR_EACH_IMM_USE_SAFE (imm_use, iter, name)
+ FOR_EACH_IMM_USE_STMT (use_stmt, iter, name)
{
- tree use_stmt = USE_STMT (imm_use);
+ bool result;
/* If the use is not in a simple assignment statement, then
there is nothing we can do. */
all = false;
continue;
}
-
- all = forward_propagate_addr_expr_1 (stmt, use_stmt) && all;
+
+ 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.
-/* Main entry point for the forward propagation optimizer. */
+ 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 (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;
/* 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_CODE (TREE_OPERAND (stmt, 1)) == ADDR_EXPR
- && TREE_CODE (TREE_OPERAND (stmt, 0)) == SSA_NAME)
+ if (TREE_CODE (stmt) == MODIFY_EXPR)
{
- if (forward_propagate_addr_expr (stmt))
- bsi_remove (&bsi);
+ 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);
if (cfg_changed)
cleanup_tree_cfg ();
+ return todoflags;
}
PROP_cfg | PROP_ssa
| PROP_alias, /* properties_required */
0, /* properties_provided */
- 0, /* properties_destroyed */
+ PROP_smt_usage, /* properties_destroyed */
0, /* todo_flags_start */
- TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */
+ TODO_dump_func /* todo_flags_finish */
+ | TODO_ggc_collect
| TODO_update_ssa | TODO_verify_ssa,
0 /* letter */
};
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