The following tries to address the inconsistency with folding
two addresses based on two decls vs. one pointer vs a decl address
caused by the latter not honoring interposition.
Honza, is
+ /* If obj1 is interposable give up. */
+ if (VAR_P (obj1)
+ && (TREE_STATIC (obj1) || DECL_EXTERNAL (obj1)))
+ {
+ varpool_node *node = varpool_node::get (obj1);
+ if (! node
+ || ! node->analyzed
+ || ! decl_binds_to_current_def_p (obj1))
+ return false;
+ }
conservatively correct? I tried to learn from
symtab_node::equal_address_to but I'm not 100% sure. Esp.
in what cases can I expect a NULL node from varpool_node::get?
Basically I am using the above to decide whether I can use
the ultimate alias target of two decls to decide whether they
are not equal (points-to uses the DECL_UID of the ultimate alias
target in the bitmaps).
Maybe you can factor out a symtab helper for me? I think I
want to catch all cases where symtab_node::equal_address_to
would return -1 (thus with respect to aliases the above doesn't
look conservative?)
Thanks,
Richard.
2016-10-19 Richard Biener <rguent...@suse.de>
PR tree-optimization/78035
* tree-ssa-alias.h (struct pt_solution): Add vars_contains_interposable
flag.
* tree-ssa-structalias.c: Include varasm.h.
(set_uids_in_ptset): Set vars_contains_interposable for
interposable variables.
(ipa_escaped_pt): Adjust.
* tree-ssa-alias.c: Include varasm.h.
(ptrs_compare_unequal): If pt->vars_contains_interposable or
a decl is interposable then do not conclude anything about
address equality.
(dump_points_to_solution): Handle vars_contains_interposable.
* gimple-pretty-print.c (pp_points_to_solution): Likewise.
* gcc.target/i386/pr78035.c: New testcase.
Index: gcc/testsuite/gcc.target/i386/pr78035.c
===================================================================
--- gcc/testsuite/gcc.target/i386/pr78035.c (revision 0)
+++ gcc/testsuite/gcc.target/i386/pr78035.c (revision 0)
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+extern int a;
+extern int b;
+extern int c;
+
+int foo(int choose_a)
+{
+ int *p;
+ if (choose_a)
+ p = &a;
+ else
+ p = &b;
+ return p != &c;
+}
+
+int bar ()
+{
+ return &a != &c;
+}
+
+/* We should not optimize away either comparison. */
+/* { dg-final { scan-assembler-times "cmp" 2 } } */
Index: gcc/tree-ssa-alias.c
===================================================================
--- gcc/tree-ssa-alias.c (revision 241362)
+++ gcc/tree-ssa-alias.c (working copy)
@@ -32,12 +32,12 @@ along with GCC; see the file COPYING3.
#include "tree-pretty-print.h"
#include "alias.h"
#include "fold-const.h"
-
#include "langhooks.h"
#include "dumpfile.h"
#include "tree-eh.h"
#include "tree-dfa.h"
#include "ipa-reference.h"
+#include "varasm.h"
/* Broad overview of how alias analysis on gimple works:
@@ -366,15 +366,39 @@ ptrs_compare_unequal (tree ptr1, tree pt
/* We may not use restrict to optimize pointer comparisons.
See PR71062. So we have to assume that restrict-pointed-to
may be in fact obj1. */
- if (!pi || pi->pt.vars_contains_restrict)
+ if (! pi
+ || pi->pt.vars_contains_restrict
+ || pi->pt.vars_contains_interposable)
return false;
+ /* If obj1 is interposable give up. */
+ if (VAR_P (obj1)
+ && (TREE_STATIC (obj1) || DECL_EXTERNAL (obj1)))
+ {
+ varpool_node *node = varpool_node::get (obj1);
+ if (! node
+ || ! node->analyzed
+ || ! decl_binds_to_current_def_p (obj1))
+ return false;
+ }
return !pt_solution_includes (&pi->pt, obj1);
}
else if (TREE_CODE (ptr1) == SSA_NAME && obj2)
{
struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr1);
- if (!pi || pi->pt.vars_contains_restrict)
+ if (! pi
+ || pi->pt.vars_contains_restrict
+ || pi->pt.vars_contains_interposable)
return false;
+ /* If obj2 is interposable give up. */
+ if (VAR_P (obj2)
+ && (TREE_STATIC (obj2) || DECL_EXTERNAL (obj2)))
+ {
+ varpool_node *node = varpool_node::get (obj2);
+ if (! node
+ || ! node->analyzed
+ || ! decl_binds_to_current_def_p (obj2))
+ return false;
+ }
return !pt_solution_includes (&pi->pt, obj2);
}
@@ -545,7 +569,12 @@ dump_points_to_solution (FILE *file, str
comma = ", ";
}
if (pt->vars_contains_restrict)
- fprintf (file, "%srestrict", comma);
+ {
+ fprintf (file, "%srestrict", comma);
+ comma = ", ";
+ }
+ if (pt->vars_contains_interposable)
+ fprintf (file, "%sinterposable", comma);
fprintf (file, ")");
}
}
Index: gcc/tree-ssa-alias.h
===================================================================
--- gcc/tree-ssa-alias.h (revision 241362)
+++ gcc/tree-ssa-alias.h (working copy)
@@ -57,6 +57,8 @@ struct GTY(()) pt_solution
/* Nonzero if the vars bitmap includes a anonymous variable used to
represent storage pointed to by a restrict qualified pointer. */
unsigned int vars_contains_restrict : 1;
+ /* Nonzero if the vars bitmap includes an interposable variable. */
+ unsigned int vars_contains_interposable : 1;
/* Set of variables that this pointer may point to. */
bitmap vars;
Index: gcc/gimple-pretty-print.c
===================================================================
--- gcc/gimple-pretty-print.c (revision 241362)
+++ gcc/gimple-pretty-print.c (working copy)
@@ -728,6 +728,12 @@ pp_points_to_solution (pretty_printer *b
{
pp_string (buffer, comma);
pp_string (buffer, "restrict");
+ comma = ", ";
+ }
+ if (pt->vars_contains_interposable)
+ {
+ pp_string (buffer, comma);
+ pp_string (buffer, "interposable");
}
pp_string (buffer, ")");
}
Index: gcc/tree-ssa-structalias.c
===================================================================
--- gcc/tree-ssa-structalias.c (revision 241362)
+++ gcc/tree-ssa-structalias.c (working copy)
@@ -39,6 +39,8 @@
#include "tree-dfa.h"
#include "params.h"
#include "gimple-walk.h"
+#include "varasm.h"
+
/* The idea behind this analyzer is to generate set constraints from the
program, then solve the resulting constraints in order to generate the
@@ -6344,6 +6346,18 @@ set_uids_in_ptset (bitmap into, bitmap f
&& fndecl
&& ! auto_var_in_fn_p (vi->decl, fndecl)))
pt->vars_contains_nonlocal = true;
+
+ /* If we have a variable that is interposable record that fact
+ for pointer comparison simplification. */
+ if (VAR_P (vi->decl)
+ && (DECL_EXTERNAL (vi->decl) || TREE_PUBLIC (vi->decl)))
+ {
+ varpool_node *node = varpool_node::get (vi->decl);
+ if (! node
+ || ! node->analyzed
+ || ! decl_binds_to_current_def_p (node->decl))
+ pt->vars_contains_interposable = true;
+ }
}
else if (TREE_CODE (vi->decl) == FUNCTION_DECL
@@ -7576,7 +7590,8 @@ make_pass_build_ealias (gcc::context *ct
/* IPA PTA solutions for ESCAPED. */
struct pt_solution ipa_escaped_pt
- = { true, false, false, false, false, false, false, false, false, NULL };
+ = { true, false, false, false, false,
+ false, false, false, false, false, NULL };
/* Associate node with varinfo DATA. Worker for
cgraph_for_symbol_thunks_and_aliases. */
