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Re: [PATCH] Alternative solution for PR36343, missed call-clobbering due to TBAA pruning of points-to sets
On Wed, 28 May 2008, Richard Guenther wrote:
> On Wed, 28 May 2008, Daniel Berlin wrote:
>
> > This is fine by me.
>
> It seems I have to track down some Ada failures with the patch, so
> don't hold your breath.
The problem was that we cannot disregard escapes to pure/const functions
as we do not track call-used variables separately.
So, this is what I committed after bootstrapping and testing on
x86_64-unknown-linux-gnu for all languages including Ada.
Thanks,
Richard.
2008-05-27 Richard Guenther <rguenther@suse.de>
PR tree-optimization/36343
PR tree-optimization/36346
PR tree-optimization/36347
* tree-flow.h (clobber_what_p_points_to): Declare.
* tree-ssa-structalias.c (set_uids_in_ptset): Whether the
pointed-to variable is dereferenced is irrelevant to whether
the pointer can access the pointed-to variable.
(clobber_what_p_points_to): New function.
* tree-ssa-alias.c (set_initial_properties): Use it.
* tree-ssa.c (verify_flow_sensitive_alias_info): Adjust
call clobber check for NMTs.
* gcc.c-torture/execute/pr36343.c: New testcase.
Index: gcc/tree-flow.h
===================================================================
*** gcc/tree-flow.h.orig 2008-05-29 10:58:13.000000000 +0200
--- gcc/tree-flow.h 2008-05-29 11:02:57.000000000 +0200
*************** tree gimple_fold_indirect_ref (tree);
*** 1167,1172 ****
--- 1167,1173 ----
/* In tree-ssa-structalias.c */
bool find_what_p_points_to (tree);
+ bool clobber_what_p_points_to (tree);
/* In tree-ssa-live.c */
extern void remove_unused_locals (void);
Index: gcc/tree-ssa-alias.c
===================================================================
*** gcc/tree-ssa-alias.c.orig 2008-05-29 10:58:13.000000000 +0200
--- gcc/tree-ssa-alias.c 2008-05-29 11:14:50.000000000 +0200
*************** set_initial_properties (struct alias_inf
*** 545,552 ****
{
struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr);
tree tag = symbol_mem_tag (SSA_NAME_VAR (ptr));
!
! if (pi->value_escapes_p)
{
/* If PTR escapes then its associated memory tags and
pointed-to variables are call-clobbered. */
--- 545,558 ----
{
struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr);
tree tag = symbol_mem_tag (SSA_NAME_VAR (ptr));
!
! /* A pointer that only escapes via a function return does not
! add to the call clobber or call used solution.
! To exclude ESCAPE_TO_PURE_CONST we would need to track
! call used variables separately or compute those properly
! in the operand scanner. */
! if (pi->value_escapes_p
! && pi->escape_mask & ~ESCAPE_TO_RETURN)
{
/* If PTR escapes then its associated memory tags and
pointed-to variables are call-clobbered. */
*************** set_initial_properties (struct alias_inf
*** 556,579 ****
if (tag)
mark_call_clobbered (tag, pi->escape_mask);
! if (pi->pt_vars)
! {
! bitmap_iterator bi;
! unsigned int j;
! EXECUTE_IF_SET_IN_BITMAP (pi->pt_vars, 0, j, bi)
! {
! tree alias = referenced_var (j);
!
! /* If you clobber one part of a structure, you
! clobber the entire thing. While this does not make
! the world a particularly nice place, it is necessary
! in order to allow C/C++ tricks that involve
! pointer arithmetic to work. */
! if (!unmodifiable_var_p (alias))
! mark_call_clobbered (alias, pi->escape_mask);
! }
! }
! else if (pi->pt_anything)
{
any_pt_anything = true;
pt_anything_mask |= pi->escape_mask;
--- 562,574 ----
if (tag)
mark_call_clobbered (tag, pi->escape_mask);
! /* Defer to points-to analysis if possible, otherwise
! clobber all addressable variables. Parameters cannot
! point to local memory though.
! ??? Properly tracking which pointers point to non-local
! memory only would make a big difference here. */
! if (!clobber_what_p_points_to (ptr)
! && !(pi->escape_mask & ESCAPE_IS_PARM))
{
any_pt_anything = true;
pt_anything_mask |= pi->escape_mask;
Index: gcc/testsuite/gcc.c-torture/execute/pr36343.c
===================================================================
*** /dev/null 1970-01-01 00:00:00.000000000 +0000
--- gcc/testsuite/gcc.c-torture/execute/pr36343.c 2008-05-29 11:02:57.000000000 +0200
***************
*** 0 ****
--- 1,32 ----
+ extern void abort (void);
+
+ void __attribute__((noinline))
+ bar (int **p)
+ {
+ float *q = (float *)p;
+ *q = 0.0;
+ }
+
+ float __attribute__((noinline))
+ foo (int b)
+ {
+ int *i = 0;
+ float f = 1.0;
+ int **p;
+ if (b)
+ p = &i;
+ else
+ p = (int **)&f;
+ bar (p);
+ if (b)
+ return **p;
+ return f;
+ }
+
+ int main()
+ {
+ if (foo(0) != 0.0)
+ abort ();
+ return 0;
+ }
+
Index: gcc/tree-ssa-structalias.c
===================================================================
*** gcc/tree-ssa-structalias.c.orig 2008-05-29 10:58:13.000000000 +0200
--- gcc/tree-ssa-structalias.c 2008-05-29 11:02:57.000000000 +0200
*************** set_uids_in_ptset (tree ptr, bitmap into
*** 4664,4680 ****
|| TREE_CODE (vi->decl) == RESULT_DECL)
{
/* Just add VI->DECL to the alias set.
! Don't type prune artificial vars. */
! if (vi->is_artificial_var)
bitmap_set_bit (into, DECL_UID (vi->decl));
else
{
alias_set_type var_alias_set, ptr_alias_set;
var_alias_set = get_alias_set (vi->decl);
ptr_alias_set = get_alias_set (TREE_TYPE (TREE_TYPE (ptr)));
! if (no_tbaa_pruning
! || (!is_derefed && !vi->directly_dereferenced)
! || alias_sets_conflict_p (ptr_alias_set, var_alias_set))
bitmap_set_bit (into, DECL_UID (vi->decl));
}
}
--- 4664,4682 ----
|| TREE_CODE (vi->decl) == RESULT_DECL)
{
/* Just add VI->DECL to the alias set.
! Don't type prune artificial vars or points-to sets
! for pointers that have not been dereferenced or with
! type-based pruning disabled. */
! if (vi->is_artificial_var
! || !is_derefed
! || no_tbaa_pruning)
bitmap_set_bit (into, DECL_UID (vi->decl));
else
{
alias_set_type var_alias_set, ptr_alias_set;
var_alias_set = get_alias_set (vi->decl);
ptr_alias_set = get_alias_set (TREE_TYPE (TREE_TYPE (ptr)));
! if (alias_sets_conflict_p (ptr_alias_set, var_alias_set))
bitmap_set_bit (into, DECL_UID (vi->decl));
}
}
*************** find_what_p_points_to (tree p)
*** 4885,4891 ****
--- 4887,4957 ----
return false;
}
+ /* Mark everything that p points to as call clobbered. Returns true
+ if everything is done and false if all addressable variables need to
+ be clobbered because p points to anything. */
+ bool
+ clobber_what_p_points_to (tree p)
+ {
+ tree lookup_p = p;
+ varinfo_t vi;
+ struct ptr_info_def *pi;
+ unsigned int i;
+ bitmap_iterator bi;
+
+ if (!have_alias_info)
+ return false;
+
+ /* For parameters, get at the points-to set for the actual parm
+ decl. */
+ if (TREE_CODE (p) == SSA_NAME
+ && TREE_CODE (SSA_NAME_VAR (p)) == PARM_DECL
+ && SSA_NAME_IS_DEFAULT_DEF (p))
+ lookup_p = SSA_NAME_VAR (p);
+
+ vi = lookup_vi_for_tree (lookup_p);
+ if (!vi)
+ return false;
+
+ /* We are asking for the points-to solution of pointers. */
+ gcc_assert (!vi->is_artificial_var
+ && vi->size == vi->fullsize);
+
+ pi = get_ptr_info (p);
+
+ /* This variable may have been collapsed, let's get the real
+ variable. */
+ vi = get_varinfo (find (vi->id));
+
+ /* Mark variables in the solution call-clobbered. */
+ EXECUTE_IF_SET_IN_BITMAP (vi->solution, 0, i, bi)
+ {
+ varinfo_t vi = get_varinfo (i);
+
+ if (vi->is_artificial_var)
+ {
+ /* nothing_id and readonly_id do not cause any
+ call clobber ops. For anything_id and integer_id
+ we need to clobber all addressable vars. */
+ if (vi->id == anything_id
+ || vi->id == integer_id)
+ return false;
+ }
+
+ /* Only artificial heap-vars are further interesting. */
+ if (vi->is_artificial_var && !vi->is_heap_var)
+ continue;
+
+ if ((TREE_CODE (vi->decl) == VAR_DECL
+ || TREE_CODE (vi->decl) == PARM_DECL
+ || TREE_CODE (vi->decl) == RESULT_DECL)
+ && !unmodifiable_var_p (vi->decl))
+ mark_call_clobbered (vi->decl, pi->escape_mask);
+ }
+
+ return true;
+ }
/* Dump points-to information to OUTFILE. */
Index: gcc/tree-ssa.c
===================================================================
*** gcc/tree-ssa.c.orig 2008-05-29 10:58:13.000000000 +0200
--- gcc/tree-ssa.c 2008-05-29 12:25:22.000000000 +0200
*************** verify_flow_sensitive_alias_info (void)
*** 571,577 ****
goto err;
}
! if (pi->value_escapes_p && pi->name_mem_tag)
{
tree t = memory_partition (pi->name_mem_tag);
if (t == NULL_TREE)
--- 571,579 ----
goto err;
}
! if (pi->value_escapes_p
! && pi->escape_mask & ~ESCAPE_TO_RETURN
! && pi->name_mem_tag)
{
tree t = memory_partition (pi->name_mem_tag);
if (t == NULL_TREE)