On Wed, 3 Sep 2014, Richard Biener wrote:
>
> Ok, so with recent activity in that mgrid bug (PR55334) I tried
> to remember what solution we thought of after determining that
> ADD_RESTRICT is a no-go.
>
> The following very prototypish patch implements the idea of
> computing known non-dependences and maintaining them over
> the compilation (mainly inlining / cloning for PR55334).
>
> So the patch piggy-backs on PTA (bad - PTA doesn't compute
> must-aliases, so it will work only for a very limited set
> of testcases now - but at least it might work for
> non-register restrict stuff).
>
> The representation of "non-dependences" is the most interesting
> bit of course. We partition memory references into different
> cliques in which all references are independent. And we
> split that clique again into sets of references based on the
> same pointer.
>
> That allows us to disambiguate equal clique but distinct pointer
> memory references.
>
> For restrict you'd put all(!) memory references in the BLOCK
> where the restrict pointer is live into the same clique
> and assign a distinct ptr based on which restrict pointer this
> is based on. You make all references not based on any
> restrict pointer have ptr == 0 (not implemented in the prototype
> patch - they don't get a clique assigned).
>
> The patch simplifies this by taking function scope as the
> only BLOCK to consider, thus inside a function the clique
> will be unique (before inlining).
>
> I can see issues arising with assigning numbers in the frontend
> based on real BLOCKs and
>
> {
> int * restrict q;
> {
> int * restrict p;
> *p = *q;
> }
> {
> int * restrict r;
> *r = *q;
> }
>
> that is, non-dependences based on pointers coming from different
> nested scopes. The FE in this case would need to "duplicate"
> the ptr value for 'q' to not make *p and *r falsely a
> non-dependence. But I think we're not planning to assign
> this in the C frontend family (maybe the Fortran FE though).
>
> To preserve correctness cliques from inlined functions need to
> be remapped to an unused clique number so struct function
> gets a max_clique number. (remapping not implemented in
> the prototype)
>
> Any correctness / missed-optimization holes to punch? That is,
> given a set of non-dependent reference pairs, can you assign
> that clique, ptr values in a correct and optimal way?
> (it somehow assumes transitivity, if the set is *a, *b; *b, *c;
> then *a, *c are also non-dependent)
>
> It all depends on a conservative but agressive must-be-based-on
> analysis of course. You'd meet that with the conservative
> may-be-based-on analysis from PTA and compute the proper
> non-dependences from that.
>
> Comments welcome.
>
> Patch tested on
>
> static inline void foo (int * __restrict__ p, int * __restrict__ q)
> {
> int i;
> for (i = 0; i < 1024; ++i)
> p[i] = q[i];
> }
>
> void bar (int *p, int *q)
> {
> foo (p, q);
> }
>
> where it still vectorizes the loop in bar without alias check.
Updated patch with a tiny fix to manage fixing PR55334 (IPA-CP
issue with mgrid) and renaming all-over-the-place.
Still lacks the clique remapping code in the inliner which is
required for correctness and still lacks code to deal with
disambiguating restrct vs. non-restrict accesses.
Improves mgrid performance by 10%, still fixes the above tiny
testcase but otherwise untested.
Richard.
2014-09-05 Richard Biener <rguent...@suse.de>
PR tree-optimization/55334
Index: trunk/gcc/function.h
===================================================================
*** trunk.orig/gcc/function.h 2014-09-05 14:05:43.799777783 +0200
--- trunk/gcc/function.h 2014-09-05 14:10:30.961758013 +0200
*************** struct GTY(()) function {
*** 593,598 ****
--- 593,601 ----
a string describing the reason for failure. */
const char * GTY((skip)) cannot_be_copied_reason;
+ /* Last assigned dependence info clique. */
+ unsigned short last_clique;
+
/* Collected bit flags. */
/* Number of units of general registers that need saving in stdarg
Index: trunk/gcc/tree-inline.c
===================================================================
*** trunk.orig/gcc/tree-inline.c 2014-09-05 14:05:43.799777783 +0200
--- trunk/gcc/tree-inline.c 2014-09-05 14:10:10.303759435 +0200
*************** remap_gimple_op_r (tree *tp, int *walk_s
*** 929,934 ****
--- 929,938 ----
TREE_THIS_VOLATILE (*tp) = TREE_THIS_VOLATILE (old);
TREE_SIDE_EFFECTS (*tp) = TREE_SIDE_EFFECTS (old);
TREE_NO_WARNING (*tp) = TREE_NO_WARNING (old);
+ /* ??? Properly remap the clique to a new one. */
+ if (MR_DEPENDENCE_CLIQUE (old) != 0)
+ MR_DEPENDENCE_CLIQUE (*tp) = MR_DEPENDENCE_CLIQUE (old);
+ MR_DEPENDENCE_BASE (*tp) = MR_DEPENDENCE_BASE (old);
/* We cannot propagate the TREE_THIS_NOTRAP flag if we have
remapped a parameter as the property might be valid only
for the parameter itself. */
*************** copy_tree_body_r (tree *tp, int *walk_su
*** 1180,1185 ****
--- 1184,1193 ----
TREE_THIS_VOLATILE (*tp) = TREE_THIS_VOLATILE (old);
TREE_SIDE_EFFECTS (*tp) = TREE_SIDE_EFFECTS (old);
TREE_NO_WARNING (*tp) = TREE_NO_WARNING (old);
+ /* ??? Properly remap the clique to a new one. */
+ if (MR_DEPENDENCE_CLIQUE (old) != 0)
+ MR_DEPENDENCE_CLIQUE (*tp) = MR_DEPENDENCE_CLIQUE (old);
+ MR_DEPENDENCE_BASE (*tp) = MR_DEPENDENCE_BASE (old);
/* We cannot propagate the TREE_THIS_NOTRAP flag if we have
remapped a parameter as the property might be valid only
for the parameter itself. */
Index: trunk/gcc/tree-pretty-print.c
===================================================================
*** trunk.orig/gcc/tree-pretty-print.c 2014-09-05 14:05:43.799777783 +0200
--- trunk/gcc/tree-pretty-print.c 2014-09-05 14:13:42.869744800 +0200
*************** dump_generic_node (pretty_printer *buffe
*** 1081,1087 ****
/* Same value types ignoring qualifiers. */
&& (TYPE_MAIN_VARIANT (TREE_TYPE (node))
== TYPE_MAIN_VARIANT
! (TREE_TYPE (TREE_TYPE (TREE_OPERAND (node, 1))))))
{
if (TREE_CODE (TREE_OPERAND (node, 0)) != ADDR_EXPR)
{
--- 1081,1088 ----
/* Same value types ignoring qualifiers. */
&& (TYPE_MAIN_VARIANT (TREE_TYPE (node))
== TYPE_MAIN_VARIANT
! (TREE_TYPE (TREE_TYPE (TREE_OPERAND (node, 1)))))
! && MR_DEPENDENCE_CLIQUE (node) == 0)
{
if (TREE_CODE (TREE_OPERAND (node, 0)) != ADDR_EXPR)
{
*************** dump_generic_node (pretty_printer *buffe
*** 1112,1117 ****
--- 1113,1125 ----
dump_generic_node (buffer, TREE_OPERAND (node, 1),
spc, flags, false);
}
+ if (MR_DEPENDENCE_CLIQUE (node) != 0)
+ {
+ pp_string (buffer, " clique ");
+ pp_unsigned_wide_integer (buffer, MR_DEPENDENCE_CLIQUE (node));
+ pp_string (buffer, " base ");
+ pp_unsigned_wide_integer (buffer, MR_DEPENDENCE_BASE (node));
+ }
pp_right_bracket (buffer);
}
break;
*************** dump_generic_node (pretty_printer *buffe
*** 1450,1456 ****
/* Same value types ignoring qualifiers. */
&& (TYPE_MAIN_VARIANT (TREE_TYPE (op0))
== TYPE_MAIN_VARIANT
! (TREE_TYPE (TREE_TYPE (TREE_OPERAND (op0, 1))))))))
{
op0 = TREE_OPERAND (op0, 0);
str = "->";
--- 1458,1465 ----
/* Same value types ignoring qualifiers. */
&& (TYPE_MAIN_VARIANT (TREE_TYPE (op0))
== TYPE_MAIN_VARIANT
! (TREE_TYPE (TREE_TYPE (TREE_OPERAND (op0, 1)))))
! && MR_DEPENDENCE_CLIQUE (op0) == 0)))
{
op0 = TREE_OPERAND (op0, 0);
str = "->";
Index: trunk/gcc/tree-ssa-alias.c
===================================================================
*** trunk.orig/gcc/tree-ssa-alias.c 2014-09-05 14:05:43.799777783 +0200
--- trunk/gcc/tree-ssa-alias.c 2014-09-05 14:10:10.304759435 +0200
*************** refs_may_alias_p_1 (ao_ref *ref1, ao_ref
*** 1371,1376 ****
--- 1371,1404 ----
return decl_refs_may_alias_p (ref1->ref, base1, offset1, max_size1,
ref2->ref, base2, offset2, max_size2);
+ /* Handle restrict based accesses.
+ ??? ao_ref_base strips inner MEM_REF [&decl], recover from that
+ here. */
+ tree rbase1 = base1;
+ tree rbase2 = base2;
+ if (var1_p)
+ {
+ rbase1 = ref1->ref;
+ if (rbase1)
+ while (handled_component_p (rbase1))
+ rbase1 = TREE_OPERAND (rbase1, 0);
+ }
+ if (var2_p)
+ {
+ rbase2 = ref2->ref;
+ if (rbase2)
+ while (handled_component_p (rbase2))
+ rbase2 = TREE_OPERAND (rbase2, 0);
+ }
+ if (rbase1 && rbase2
+ && (TREE_CODE (base1) == MEM_REF || TREE_CODE (base1) == TARGET_MEM_REF)
+ && (TREE_CODE (base2) == MEM_REF || TREE_CODE (base2) == TARGET_MEM_REF)
+ /* If the accesses are in the same restrict clique... */
+ && MR_DEPENDENCE_CLIQUE (base1) == MR_DEPENDENCE_CLIQUE (base2)
+ /* But based on different pointers they do not alias. */
+ && MR_DEPENDENCE_BASE (base1) != MR_DEPENDENCE_BASE (base2))
+ return false;
+
ind1_p = (TREE_CODE (base1) == MEM_REF
|| TREE_CODE (base1) == TARGET_MEM_REF);
ind2_p = (TREE_CODE (base2) == MEM_REF
Index: trunk/gcc/tree-ssa-structalias.c
===================================================================
*** trunk.orig/gcc/tree-ssa-structalias.c 2014-09-05 14:05:43.799777783
+0200
--- trunk/gcc/tree-ssa-structalias.c 2014-09-05 14:25:22.078696660 +0200
***************
*** 52,57 ****
--- 52,60 ----
#include "splay-tree.h"
#include "params.h"
#include "alias.h"
+ #include "tree-phinodes.h"
+ #include "ssa-iterators.h"
+ #include "tree-pretty-print.h"
/* The idea behind this analyzer is to generate set constraints from the
program, then solve the resulting constraints in order to generate the
*************** struct variable_info
*** 272,283 ****
--- 275,293 ----
/* True if this field has only restrict qualified pointers. */
unsigned int only_restrict_pointers : 1;
+ /* True if this represents a heap var created for a restrict qualified
+ pointer. */
+ unsigned int is_restrict_var : 1;
+
/* True if this represents a global variable. */
unsigned int is_global_var : 1;
/* True if this represents a IPA function info. */
unsigned int is_fn_info : 1;
+ /* ??? Store somewhere better. */
+ unsigned short ruid;
+
/* The ID of the variable for the next field in this structure
or zero for the last field in this structure. */
unsigned next;
*************** new_var_info (tree t, const char *name)
*** 369,374 ****
--- 379,385 ----
ret->is_heap_var = false;
ret->may_have_pointers = true;
ret->only_restrict_pointers = false;
+ ret->is_restrict_var = false;
ret->is_global_var = (t == NULL_TREE);
ret->is_fn_info = false;
if (t && DECL_P (t))
*************** static varinfo_t
*** 3773,3778 ****
--- 3784,3790 ----
make_constraint_from_restrict (varinfo_t lhs, const char *name)
{
varinfo_t vi = make_heapvar (name);
+ vi->is_restrict_var = 1;
vi->is_global_var = 1;
vi->may_have_pointers = 1;
make_constraint_from (lhs, vi->id);
*************** intra_create_variable_infos (struct func
*** 5845,5850 ****
--- 5857,5863 ----
tree heapvar = build_fake_var_decl (TREE_TYPE (TREE_TYPE (t)));
DECL_EXTERNAL (heapvar) = 1;
vi = create_variable_info_for_1 (heapvar, "PARM_NOALIAS");
+ vi->is_restrict_var = 1;
insert_vi_for_tree (heapvar, vi);
lhsc.var = p->id;
lhsc.type = SCALAR;
*************** compute_may_aliases (void)
*** 6948,6953 ****
--- 6961,7061 ----
if (dump_file)
dump_alias_info (dump_file);
+ {
+ unsigned short clique = 0;
+ unsigned short last_ruid = 0;
+ for (unsigned i = 0; i < num_ssa_names; ++i)
+ {
+ tree ptr = ssa_name (i);
+ if (!ptr || !POINTER_TYPE_P (TREE_TYPE (ptr)))
+ continue;
+
+ /* Avoid all this when ptr is not dereferenced? */
+ tree p = ptr;
+ if (SSA_NAME_IS_DEFAULT_DEF (ptr)
+ && (TREE_CODE (SSA_NAME_VAR (ptr)) == PARM_DECL
+ || TREE_CODE (SSA_NAME_VAR (ptr)) == RESULT_DECL))
+ p = SSA_NAME_VAR (ptr);
+
+ varinfo_t vi = get_varinfo (find (lookup_vi_for_tree (p)->id));
+ bitmap_iterator bi;
+ unsigned j;
+ varinfo_t restrict_var = NULL;
+ EXECUTE_IF_SET_IN_BITMAP (vi->solution, 0, j, bi)
+ {
+ varinfo_t oi = get_varinfo (j);
+ if (oi->is_restrict_var)
+ {
+ if (restrict_var)
+ {
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, "found restrict pointed-to "
+ "for ");
+ print_generic_expr (dump_file, ptr, 0);
+ fprintf (dump_file, " but not exclusively\n");
+ }
+ restrict_var = NULL;
+ break;
+ }
+ restrict_var = oi;
+ }
+ /* NULL is the only other valid points-to entry. */
+ else if (oi->id != nothing_id)
+ {
+ restrict_var = NULL;
+ break;
+ }
+ }
+ /* Ok, found that ptr must(!) point to a single(!) restrict
+ variable. */
+ /* ??? PTA isn't really a proper propagation engine to compute
+ this property.
+ ??? We can handle merging of two restricts
+ by unifying them. */
+ if (restrict_var)
+ {
+ if (clique == 0)
+ clique = ++cfun->last_clique;
+ if (restrict_var->ruid == 0)
+ restrict_var->ruid = ++last_ruid;
+
+ /* Now look at possible dereferences of ptr. */
+ imm_use_iterator ui;
+ gimple use_stmt;
+ FOR_EACH_IMM_USE_STMT (use_stmt, ui, ptr)
+ {
+ /* ??? Calls and asms. */
+ if (!gimple_assign_single_p (use_stmt))
+ continue;
+ tree *ref = gimple_assign_lhs_ptr (use_stmt);
+ while (handled_component_p (*ref))
+ ref = &TREE_OPERAND (*ref, 0);
+ if (TREE_CODE (*ref) == MEM_REF
+ && TREE_OPERAND (*ref, 0) == ptr)
+ {
+ MR_DEPENDENCE_CLIQUE (*ref) = clique;
+ MR_DEPENDENCE_BASE (*ref) = restrict_var->ruid;
+ }
+ ref = gimple_assign_rhs1_ptr (use_stmt);
+ while (handled_component_p (*ref))
+ ref = &TREE_OPERAND (*ref, 0);
+ if (TREE_CODE (*ref) == MEM_REF
+ && TREE_OPERAND (*ref, 0) == ptr)
+ {
+ MR_DEPENDENCE_CLIQUE (*ref) = clique;
+ MR_DEPENDENCE_BASE (*ref) = restrict_var->ruid;
+ }
+ }
+
+ /* ??? Accesses not based on a restrict pointer should
+ all get into the clique but share a single ptr ID.
+ That way they get disabiguated against restrict
+ accesses but not against each other. */
+ }
+ }
+ }
+
/* Deallocate memory used by aliasing data structures and the internal
points-to solution. */
delete_points_to_sets ();
Index: trunk/gcc/tree-data-ref.c
===================================================================
*** trunk.orig/gcc/tree-data-ref.c 2014-09-05 14:05:43.799777783 +0200
--- trunk/gcc/tree-data-ref.c 2014-09-05 14:10:10.306759435 +0200
*************** dr_analyze_indices (struct data_referenc
*** 980,988 ****
--- 980,991 ----
guaranteed.
As a band-aid, mark the access so we can special-case
it in dr_may_alias_p. */
+ tree old = ref;
ref = fold_build2_loc (EXPR_LOCATION (ref),
MEM_REF, TREE_TYPE (ref),
base, memoff);
+ MR_DEPENDENCE_CLIQUE (ref) = MR_DEPENDENCE_CLIQUE (old);
+ MR_DEPENDENCE_BASE (ref) = MR_DEPENDENCE_BASE (old);
access_fns.safe_push (access_fn);
}
}
*************** dr_may_alias_p (const struct data_refere
*** 1389,1394 ****
--- 1392,1403 ----
return false;
}
+ if ((TREE_CODE (addr_a) == MEM_REF || TREE_CODE (addr_a) == TARGET_MEM_REF)
+ && (TREE_CODE (addr_b) == MEM_REF || TREE_CODE (addr_b) ==
TARGET_MEM_REF)
+ && MR_DEPENDENCE_CLIQUE (addr_a) == MR_DEPENDENCE_CLIQUE (addr_b)
+ && MR_DEPENDENCE_BASE (addr_a) != MR_DEPENDENCE_BASE (addr_b))
+ return false;
+
/* If we had an evolution in a pointer-based MEM_REF BASE_OBJECT we
do not know the size of the base-object. So we cannot do any
offset/overlap based analysis but have to rely on points-to
Index: trunk/gcc/tree-core.h
===================================================================
*** trunk.orig/gcc/tree-core.h 2014-09-05 14:05:43.799777783 +0200
--- trunk/gcc/tree-core.h 2014-09-05 14:10:10.306759435 +0200
*************** struct GTY(()) tree_base {
*** 802,807 ****
--- 802,817 ----
/* Internal function code. */
enum internal_fn ifn;
+
+ /* The following two fields are used for MEM_REF and TARGET_MEM_REF
+ expression trees and specify known data non-dependences. For
+ two memory references in a function they are known to not
+ alias if dependence_info.clique are equal and dependence_info.base
+ are distinct. */
+ struct {
+ unsigned short clique;
+ unsigned short base;
+ } dependence_info;
} GTY((skip(""))) u;
};
Index: trunk/gcc/tree.h
===================================================================
*** trunk.orig/gcc/tree.h 2014-09-05 14:05:43.799777783 +0200
--- trunk/gcc/tree.h 2014-09-05 14:10:10.307759435 +0200
*************** extern void protected_set_expr_location
*** 1081,1086 ****
--- 1081,1091 ----
#define TMR_STEP(NODE) (TREE_OPERAND (TARGET_MEM_REF_CHECK (NODE), 3))
#define TMR_INDEX2(NODE) (TREE_OPERAND (TARGET_MEM_REF_CHECK (NODE), 4))
+ #define MR_DEPENDENCE_CLIQUE(NODE) \
+ (TREE_CHECK2 (NODE, MEM_REF, TARGET_MEM_REF)->base.u.dependence_info.clique)
+ #define MR_DEPENDENCE_BASE(NODE) \
+ (TREE_CHECK2 (NODE, MEM_REF, TARGET_MEM_REF)->base.u.dependence_info.base)
+
/* The operands of a BIND_EXPR. */
#define BIND_EXPR_VARS(NODE) (TREE_OPERAND (BIND_EXPR_CHECK (NODE), 0))
#define BIND_EXPR_BODY(NODE) (TREE_OPERAND (BIND_EXPR_CHECK (NODE), 1))
