This moves looking at a functions fnspec to decide whether parameters
point to read-only memory and do alias disambiugations based on that
from a "hack" in VN to generic alias code.
This is to avoid regressions with a fix for PR87132 but looks useful
generally.
Bootstrap & regtest running on x86_64-unknown-linux-gnu.
Richard.
2018-08-29 Richard Biener <rguent...@suse.de>
* tree-core.h: Document use of deprecated_flag in SSA_NAME.
* tree.h (SSA_NAME_POINTS_TO_READONLY_MEMORY): Define.
* tree-into-ssa.c (pass_build_ssa::execute): Initialize
function parameters SSA_NAME_POINTS_TO_READONLY_MEMORY from fnspec.
* tree-ssa-sccvn.c (const_parms, init_const_parms): Remove.
(vn_reference_lookup_3): Remove use of const_parms.
(free_rpo_vn): Do not free const_parms.
(do_rpo_vn): Do not call init_const_parms.
* tree-ssa-alias.c (refs_may_alias_p_1): Honor
SSA_NAME_POINTS_TO_READONLY_MEMORY.
(call_may_clobber_ref_p_1): Likewise.
Index: gcc/tree-core.h
===================================================================
--- gcc/tree-core.h (revision 263944)
+++ gcc/tree-core.h (working copy)
@@ -1238,6 +1238,9 @@ struct GTY(()) tree_base {
IDENTIFIER_TRANSPARENT_ALIAS in
IDENTIFIER_NODE
+ SSA_NAME_POINTS_TO_READONLY_MEMORY in
+ SSA_NAME
+
visited:
TREE_VISITED in
Index: gcc/tree.h
===================================================================
--- gcc/tree.h (revision 263944)
+++ gcc/tree.h (working copy)
@@ -1743,6 +1743,13 @@ extern tree maybe_wrap_with_location (tr
#define SSA_NAME_IS_DEFAULT_DEF(NODE) \
SSA_NAME_CHECK (NODE)->base.default_def_flag
+/* Nonzero if this SSA_NAME is known to point to memory that may not
+ be written to. This is set for default defs of function parameters
+ that have a corresponding r or R specification in the functions
+ fn spec attribute. This is used by alias analysis. */
+#define SSA_NAME_POINTS_TO_READONLY_MEMORY(NODE) \
+ SSA_NAME_CHECK (NODE)->base.deprecated_flag
+
/* Attributes for SSA_NAMEs for pointer-type variables. */
#define SSA_NAME_PTR_INFO(N) \
SSA_NAME_CHECK (N)->ssa_name.info.ptr_info
Index: gcc/tree-into-ssa.c
===================================================================
--- gcc/tree-into-ssa.c (revision 263944)
+++ gcc/tree-into-ssa.c (working copy)
@@ -2490,6 +2490,28 @@ pass_build_ssa::execute (function *fun)
SET_SSA_NAME_VAR_OR_IDENTIFIER (name, DECL_NAME (decl));
}
+ /* Initialize SSA_NAME_POINTS_TO_READONLY_MEMORY. */
+ tree fnspec = lookup_attribute ("fn spec",
+ TYPE_ATTRIBUTES (TREE_TYPE (fun->decl)));
+ if (fnspec)
+ {
+ fnspec = TREE_VALUE (TREE_VALUE (fnspec));
+ unsigned i = 1;
+ for (tree arg = DECL_ARGUMENTS (cfun->decl);
+ arg; arg = DECL_CHAIN (arg), ++i)
+ {
+ if (i >= (unsigned) TREE_STRING_LENGTH (fnspec))
+ break;
+ if (TREE_STRING_POINTER (fnspec)[i] == 'R'
+ || TREE_STRING_POINTER (fnspec)[i] == 'r')
+ {
+ tree name = ssa_default_def (fun, arg);
+ if (name)
+ SSA_NAME_POINTS_TO_READONLY_MEMORY (name) = 1;
+ }
+ }
+ }
+
return 0;
}
Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c (revision 263945)
+++ gcc/tree-ssa-sccvn.c (working copy)
@@ -133,7 +133,6 @@ along with GCC; see the file COPYING3.
static tree *last_vuse_ptr;
static vn_lookup_kind vn_walk_kind;
static vn_lookup_kind default_vn_walk_kind;
-bitmap const_parms;
/* vn_nary_op hashtable helpers. */
@@ -1863,18 +1864,6 @@ vn_reference_lookup_3 (ao_ref *ref, tree
bool lhs_ref_ok = false;
poly_int64 copy_size;
- /* If the reference is based on a parameter that was determined as
- pointing to readonly memory it doesn't change. */
- if (TREE_CODE (base) == MEM_REF
- && TREE_CODE (TREE_OPERAND (base, 0)) == SSA_NAME
- && SSA_NAME_IS_DEFAULT_DEF (TREE_OPERAND (base, 0))
- && bitmap_bit_p (const_parms,
- SSA_NAME_VERSION (TREE_OPERAND (base, 0))))
- {
- *disambiguate_only = true;
- return NULL;
- }
-
/* First try to disambiguate after value-replacing in the definitions LHS.
*/
if (is_gimple_assign (def_stmt))
{
@@ -4514,37 +4503,6 @@ set_hashtable_value_ids (void)
set_value_id_for_result (vr->result, &vr->value_id);
}
-
-/* Allocate and initialize CONST_PARAMS, a bitmap of parameter default defs
- we know point to readonly memory. */
-
-static void
-init_const_parms ()
-{
- /* Collect pointers we know point to readonly memory. */
- const_parms = BITMAP_ALLOC (NULL);
- tree fnspec = lookup_attribute ("fn spec",
- TYPE_ATTRIBUTES (TREE_TYPE (cfun->decl)));
- if (fnspec)
- {
- fnspec = TREE_VALUE (TREE_VALUE (fnspec));
- unsigned i = 1;
- for (tree arg = DECL_ARGUMENTS (cfun->decl);
- arg; arg = DECL_CHAIN (arg), ++i)
- {
- if (i >= (unsigned) TREE_STRING_LENGTH (fnspec))
- break;
- if (TREE_STRING_POINTER (fnspec)[i] == 'R'
- || TREE_STRING_POINTER (fnspec)[i] == 'r')
- {
- tree name = ssa_default_def (cfun, arg);
- if (name)
- bitmap_set_bit (const_parms, SSA_NAME_VERSION (name));
- }
- }
- }
-}
-
/* Return the maximum value id we have ever seen. */
unsigned int
@@ -5606,8 +5564,6 @@ free_rpo_vn (void)
obstack_free (&vn_tables_obstack, NULL);
obstack_free (&vn_tables_insert_obstack, NULL);
- BITMAP_FREE (const_parms);
-
vn_ssa_aux_iterator_type it;
vn_ssa_aux_t info;
FOR_EACH_HASH_TABLE_ELEMENT (*vn_ssa_aux_hash, info, vn_ssa_aux_t, it)
@@ -6326,7 +6277,6 @@ do_rpo_vn (function *fn, edge entry, bit
unsigned region_size = (((unsigned HOST_WIDE_INT)n * num_ssa_names)
/ (n_basic_blocks_for_fn (fn) - NUM_FIXED_BLOCKS));
VN_TOP = create_tmp_var_raw (void_type_node, "vn_top");
- init_const_parms ();
vn_ssa_aux_hash = new hash_table <vn_ssa_aux_hasher> (region_size * 2);
gcc_obstack_init (&vn_ssa_aux_obstack);
Index: gcc/tree-ssa-alias.c
===================================================================
--- gcc/tree-ssa-alias.c (revision 263944)
+++ gcc/tree-ssa-alias.c (working copy)
@@ -1483,6 +1483,16 @@ refs_may_alias_p_1 (ao_ref *ref1, ao_ref
ao_ref_alias_set (ref2)))
return false;
+ /* If the reference is based on a pointer that points to memory
+ that may not be written to then the other reference cannot possibly
+ clobber it. */
+ if ((TREE_CODE (TREE_OPERAND (base2, 0)) == SSA_NAME
+ && SSA_NAME_POINTS_TO_READONLY_MEMORY (TREE_OPERAND (base2, 0)))
+ || (ind1_p
+ && TREE_CODE (TREE_OPERAND (base1, 0)) == SSA_NAME
+ && SSA_NAME_POINTS_TO_READONLY_MEMORY (TREE_OPERAND (base1, 0))))
+ return false;
+
/* Dispatch to the pointer-vs-decl or pointer-vs-pointer disambiguators. */
if (var1_p && ind2_p)
return indirect_ref_may_alias_decl_p (ref2->ref, base2,
@@ -1991,6 +2001,14 @@ call_may_clobber_ref_p_1 (gcall *call, a
|| !is_global_var (base)))
return false;
+ /* If the reference is based on a pointer that points to memory
+ that may not be written to then the call cannot possibly clobber it. */
+ if ((TREE_CODE (base) == MEM_REF
+ || TREE_CODE (base) == TARGET_MEM_REF)
+ && TREE_CODE (TREE_OPERAND (base, 0)) == SSA_NAME
+ && SSA_NAME_POINTS_TO_READONLY_MEMORY (TREE_OPERAND (base, 0)))
+ return false;
+
callee = gimple_call_fndecl (call);
/* Handle those builtin functions explicitly that do not act as
