On 09/25/2011 10:57 AM, Richard Guenther wrote: > On Sat, Sep 24, 2011 at 5:29 PM, Eric Botcazou <ebotca...@adacore.com> wrote: >>> This is an updated version of the patch. I have 2 new patches and an >>> updated testcase which I will sent out individually. >>> >>> Patch set was bootstrapped and reg-tested on x86_64. >>> >>> Ok for trunk? >>> >>> Thanks, >>> - Tom >>> >>> 2011-07-30 Tom de Vries <t...@codesourcery.com> >>> >>> PR middle-end/43513 >>> * Makefile.in (tree-ssa-ccp.o): Add $(PARAMS_H) to rule. >>> * tree-ssa-ccp.c (params.h): Include. >>> (fold_builtin_alloca_for_var): New function. >>> (ccp_fold_stmt): Use fold_builtin_alloca_for_var. >> >> We have detected another fallout on some Ada code: the transformation >> replaces >> a call to __builtin_alloca with &var, i.e. it introduces an aliased variable, >> which invalidates the points-to information of some subsequent call, fooling >> DSE into thinking that it can eliminate a live store. > > Ugh, yeah. I suppose PTA assigned a HEAP var as pointed-to object for the > original pointer, even if the transformed stmt > > orig_ptr_1 = &a; > > has the points-to information preserved for orig_ptr_1 further propagation of > &a will make accesses through orig_ptr_1 have different alias properties. > > What should work in this special case of a singleton points-to set of > orig_ptr_1 > (might want to check that) is, do > > SET_DECL_PT_UID (decl-of-a, DECL_UID (pointed-to orig_ptr_1)); > > The brute force approach is not acceptable (it'll wreck IPA points-to info). > > A helper like pt_solution_singleton_p (struct pt_solution *pt, unsigned *uid) > whould be nice to have for this. > > Note that we don't have points-to information computed during the first > CCP pass, so the above should be conditional on SSA_NAME_PTR_INFO > being present and not ! ->anything (but then assert that we actually do have > a singleton, or fail the folding). >
I tried to implement the approach you describe above in attached patch. Currently testing on x86_64. Thanks, - Tom > Richard. > >> The brute force approach >> >> Index: tree-ssa-ccp.c >> =================================================================== >> --- tree-ssa-ccp.c (revision 179038) >> +++ tree-ssa-ccp.c (working copy) >> @@ -2014,7 +2014,10 @@ do_ssa_ccp (void) >> ccp_initialize (); >> ssa_propagate (ccp_visit_stmt, ccp_visit_phi_node); >> if (ccp_finalize ()) >> - return (TODO_cleanup_cfg | TODO_update_ssa | TODO_remove_unused_locals); >> + return (TODO_cleanup_cfg >> + | TODO_update_ssa >> + | TODO_rebuild_alias >> + | TODO_remove_unused_locals); >> else >> return 0; >> } >> >> works, but we might want to be move clever. Thoughts? >> >> -- >> Eric Botcazou >>
Index: gcc/tree-ssa-ccp.c =================================================================== --- gcc/tree-ssa-ccp.c (revision 179043) +++ gcc/tree-ssa-ccp.c (working copy) @@ -1729,6 +1729,17 @@ fold_builtin_alloca_for_var (gimple stmt array_type = build_array_type_nelts (elem_type, n_elem); var = create_tmp_var (array_type, NULL); DECL_ALIGN (var) = align; + { + struct ptr_info_def *pi = SSA_NAME_PTR_INFO (lhs); + if (pi != NULL && !pi->pt.anything) + { + bool singleton_p; + unsigned uid; + singleton_p = pt_solution_singleton_p (&pi->pt, &uid); + gcc_assert (singleton_p); + SET_DECL_PT_UID (var, uid); + } + } /* Fold alloca to the address of the array. */ return fold_convert (TREE_TYPE (lhs), build_fold_addr_expr (var)); Index: gcc/tree-ssa-alias.h =================================================================== --- gcc/tree-ssa-alias.h (revision 179043) +++ gcc/tree-ssa-alias.h (working copy) @@ -126,6 +126,7 @@ extern void dump_alias_stats (FILE *); /* In tree-ssa-structalias.c */ extern unsigned int compute_may_aliases (void); extern bool pt_solution_empty_p (struct pt_solution *); +extern bool pt_solution_singleton_p (struct pt_solution *, unsigned *); extern bool pt_solution_includes_global (struct pt_solution *); extern bool pt_solution_includes (struct pt_solution *, const_tree); extern bool pt_solutions_intersect (struct pt_solution *, struct pt_solution *); Index: gcc/tree-ssa-structalias.c =================================================================== --- gcc/tree-ssa-structalias.c (revision 179043) +++ gcc/tree-ssa-structalias.c (working copy) @@ -5978,6 +5978,21 @@ pt_solution_empty_p (struct pt_solution return true; } +/* Return true if the points-to solution *PT only point to a single var, and + return the var uid in *UID. */ + +bool +pt_solution_singleton_p (struct pt_solution *pt, unsigned *uid) +{ + if (pt->anything || pt->nonlocal || pt->escaped || pt->ipa_escaped + || pt->null || pt->vars == NULL + || !bitmap_single_bit_set_p (pt->vars)) + return false; + + *uid = bitmap_first_set_bit (pt->vars); + return true; +} + /* Return true if the points-to solution *PT includes global memory. */ bool