Index: df-problems.c =================================================================== --- df-problems.c (revision 142954) +++ df-problems.c (working copy) @@ -1001,22 +1001,32 @@ df_lr_transfer_function (int bb_index) /* Run the fast dce as a side effect of building LR. */ static void -df_lr_finalize (bitmap all_blocks ATTRIBUTE_UNUSED) +df_lr_finalize (bitmap all_blocks) { if (df->changeable_flags & DF_LR_RUN_DCE) { run_fast_df_dce (); - if (df_lr->problem_data && df_lr->solutions_dirty) + + /* If dce deletes some instructions, we need to recompute the lr + solution before proceeding further. The problem is that fast + dce is a pessimestic dataflow algorithm. In the case where + it deletes a statement S inside of a loop, the uses inside of + S may not be deleted from the dataflow solution because they + were carried around the loop. While it is conservatively + correct to leave these extra bits, the standards of df + require that we maintain the best possible (least fixed + point) solution. The only way to do that is to redo the + iteration from the beginning. See PR35805 for an + example. */ + if (df_lr->solutions_dirty) { - /* If we are here, then it is because we are both verifying - the solution and the dce changed the function. In that case - the verification info built will be wrong. So we leave the - dirty flag true so that the verifier will skip the checking - part and just clean up.*/ - df_lr->solutions_dirty = true; + df_clear_flags (DF_LR_RUN_DCE); + df_lr_alloc (all_blocks); + df_lr_local_compute (all_blocks); + df_worklist_dataflow (df_lr, all_blocks, df->postorder, df->n_blocks); + df_lr_finalize (all_blocks); + df_set_flags (DF_LR_RUN_DCE); } - else - df_lr->solutions_dirty = false; } else df_lr->solutions_dirty = false; Index: dce.c =================================================================== --- dce.c (revision 142954) +++ dce.c (working copy) @@ -601,7 +601,7 @@ dce_process_block (basic_block bb, bool if (dump_file) { - fprintf (dump_file, "processing block %d live out = ", bb->index); + fprintf (dump_file, "processing block %d lr out = ", bb->index); df_print_regset (dump_file, DF_LR_OUT (bb)); }