/* 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)))
if (TREE_CODE (TREE_OPERAND (stmt, 1)) == ADDR_EXPR)
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
TREE_OPERAND (lhs, 0) = unshare_expr (TREE_OPERAND (stmt, 1));
fold_stmt_inplace (use_stmt);
tidy_after_forward_propagate_addr (use_stmt);
- return 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 (TREE_CODE (rhs) == ADDR_EXPR)
{
if (forward_propagate_addr_expr (stmt))
- bsi_remove (&bsi);
+ bsi_remove (&bsi, true);
else
bsi_next (&bsi);
}
PROP_cfg | PROP_ssa
| PROP_alias, /* properties_required */
0, /* properties_provided */
- 0, /* properties_destroyed */
+ PROP_tmt_usage, /* properties_destroyed */
0, /* todo_flags_start */
- TODO_dump_func | TODO_ggc_collect /* todo_flags_finish */
+ TODO_update_tmt_usage |TODO_dump_func /* todo_flags_finish */
+ | TODO_ggc_collect
| TODO_update_ssa | TODO_verify_ssa,
0 /* letter */
};
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