This patch tries to improve alias-analysis between an SSA_NAME and
a declaration a little. For a case like:
int array1[10], array2[10];
ptr1 = array1 + x;
ptr2 = ptr1 + y;
, *ptr2 should not alias with array2.
If we can't disambiguate from points-to information, this patch
tries to find a determined ADDR_EXPR following the defining
statements and then disambiguate by compare_base_decls. On spec2017
502.gcc, there are several thousands of new non-aliasing relation
found. (No obvious improvements or regressions found, though.)
Bootstrapped and tested on aarch64-unknown-linux-gnu.
Thanks,
Di Zhao
gcc/ChangeLog:
* tree-ssa-alias.cc (ptr_deref_may_alias_decl_p): try
to find ADDR_EXPR for SSA_NAME ptrs.
---
gcc/tree-ssa-alias.cc | 42 ++++++++++++++++++++++++++++++++++--------
1 file changed, 34 insertions(+), 8 deletions(-)
diff --git a/gcc/tree-ssa-alias.cc b/gcc/tree-ssa-alias.cc
index cf38fe506a8..a6fe1e7b227 100644
--- a/gcc/tree-ssa-alias.cc
+++ b/gcc/tree-ssa-alias.cc
@@ -271,6 +271,38 @@ ptr_deref_may_alias_decl_p (tree ptr, tree decl)
return ptr_deref_may_alias_decl_p (ptr, decl);
}
+ if (TREE_CODE (ptr) == SSA_NAME)
+ {
+ /* First disambiguate from points-to information. */
+ pi = SSA_NAME_PTR_INFO (ptr);
+ if (pi && !pt_solution_includes (&pi->pt, decl))
+ return false;
+
+ /* Try to find an ADDR_EXPR by walking the defining statements, so we can
+ probably disambiguate from compare_base_decls. */
+ gimple *def_stmt;
+ while ((def_stmt = SSA_NAME_DEF_STMT (ptr)))
+ {
+ if (is_gimple_assign (def_stmt)
+ && gimple_assign_rhs_code (def_stmt) == POINTER_PLUS_EXPR)
+ {
+ ptr = gimple_assign_rhs1 (def_stmt);
+ if (TREE_CODE (ptr) != SSA_NAME)
+ break;
+ }
+ /* See if we can find a certain defining source. */
+ else if (gimple_code (def_stmt) == GIMPLE_PHI
+ && gimple_phi_num_args (def_stmt) == 1)
+ {
+ ptr = PHI_ARG_DEF (def_stmt, 0);
+ if (TREE_CODE (ptr) != SSA_NAME)
+ break;
+ }
+ else
+ break;
+ }
+ }
+
/* ADDR_EXPR pointers either just offset another pointer or directly
specify the pointed-to set. */
if (TREE_CODE (ptr) == ADDR_EXPR)
@@ -279,7 +311,7 @@ ptr_deref_may_alias_decl_p (tree ptr, tree decl)
if (base
&& (TREE_CODE (base) == MEM_REF
|| TREE_CODE (base) == TARGET_MEM_REF))
- ptr = TREE_OPERAND (base, 0);
+ return ptr_deref_may_alias_decl_p (TREE_OPERAND (base, 0), decl);
else if (base
&& DECL_P (base))
return compare_base_decls (base, decl) != 0;
@@ -294,13 +326,7 @@ ptr_deref_may_alias_decl_p (tree ptr, tree decl)
if (!may_be_aliased (decl))
return false;
- /* If we do not have useful points-to information for this pointer
- we cannot disambiguate anything else. */
- pi = SSA_NAME_PTR_INFO (ptr);
- if (!pi)
- return true;
-
- return pt_solution_includes (&pi->pt, decl);
+ return true;
}
/* Return true if dereferenced PTR1 and PTR2 may alias.
--
2.25.1
