[Bug tree-optimization/21639] poisoned ggc memory used for -ftree-vectorize

[dorit at il dot ibm dot com]

------- Additional Comments From dorit at il dot ibm dot com  2005-05-24 11:53 -------
I can reproduce this problem on powerpc-apple-darwin, even without the 
options "-maltivec -mabi-altivec" (which means that no simd vectorization takes 
place). What happens is that the scalar_evolution_info hash table is corrupted 
between vectorization pass and tree_unroll_loops_completely pass. It looks like 
this corruption takes place during pass_lower_vector_ssa (which is enabled by -
ftree-vectorize), when executing the todo_flags_finish for this pass.

The scalar_evolution_info htab before pass_lower_vector_ssa looks like this:

==============================
after execute pass:
(classify_chrec {0, +, 1}_1
  affine_univariate
)
(classify_chrec 
(classify_chrec {1, +, 1}_2
  affine_univariate
) 
(classify_chrec {0, +, 1}_2
  affine_univariate
)

( 
-----------------------------------------
3       affine univariate chrecs
0       affine multivariate chrecs
0       degree greater than 2 polynomials
0       chrec_dont_know chrecs
-----------------------------------------
4       total chrecs
1       with undetermined coefficients
-----------------------------------------
21      chrecs in the scev database
55      sets in the scev database
73      gets in the scev database
-----------------------------------------
)
==============================


After pass_lower_vector_ssa the scalar_evolution_info htab looks like this:

==============================
(classify_chrec <<< Unknown tree:  >>>

)
(classify_chrec
(classify_chrec <<< Unknown tree:  >>>

)
(classify_chrec <<< Unknown tree:  >>>

)

(
-----------------------------------------
0       affine univariate chrecs
0       affine multivariate chrecs
0       degree greater than 2 polynomials
0       chrec_dont_know chrecs
-----------------------------------------
4       total chrecs
1       with undetermined coefficients
-----------------------------------------
21      chrecs in the scev database
55      sets in the scev database
73      gets in the scev database
-----------------------------------------
)
==============================


Removing the "TODO_ggc_collect" from the todo_flags_finish of 
pass_lower_vector_ssa solves the problem (in tree-complex.c):

==============================
 struct tree_opt_pass pass_lower_vector_ssa = 
 {
   "veclower",                          /* name */
   gate_expand_vector_operations,       /* gate */
   expand_vector_operations,            /* execute */
   NULL,                                        /* sub */
   NULL,                                        /* next */
   0,                                   /* static_pass_number */
   0,                                   /* tv_id */
   PROP_cfg,                            /* properties_required */
   0,                                   /* properties_provided */
   0,                                   /* properties_destroyed */
   0,                                   /* todo_flags_start */
   TODO_dump_func | TODO_update_ssa     /* todo_flags_finish */
-    | TODO_ggc_collect | TODO_verify_ssa
+    | TODO_verify_ssa
     | TODO_verify_stmts | TODO_verify_flow,
   0                                    /* letter */
 };
==============================

Paolo, is the above solution ok with you? If so, I'll go ahead and prepare a 
patch. Alternatively, if ggc_collect is really required here, then adding a 
call to scev_reset() would also solve the problem (again, in tree-complex.c):

==============================
 expand_vector_operations (void)
 {
   block_stmt_iterator bsi;
   basic_block bb;
 
   FOR_EACH_BB (bb)
     {
       for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
        {
          expand_vector_operations_1 (&bsi);
          update_stmt_if_modified (bsi_stmt (bsi));
        }
     }
+
+  scev_reset ();
+
 }
==============================

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |paolo dot bonzini at lu dot
                   |                            |unisi dot ch


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21639