mono/mini/branch-opts.c

   1 /*
   2  * branch-opts.c: Branch optimizations support
   3  *
   4  * Authors:
   5  *   Patrik Torstensson (Patrik.Torstesson at gmail.com)
   6  *
   7  * (C) 2005 Ximian, Inc.  http://www.ximian.com
   8  */
   9  #include "mini.h"
  10
  11  /*
  12  * Used by the arch code to replace the exception handling
  13  * with a direct branch. This is safe to do if the
  14  * exception object isn't used, no rethrow statement and
  15  * no filter statement (verify).
  16  *
  17  */
  18 MonoInst *
  19 mono_branch_optimize_exception_target (MonoCompile *cfg, MonoBasicBlock *bb, const char * exname)
  20 {
  21         MonoMethod *method = cfg->method;
  22         MonoMethodHeader *header = mono_method_get_header (method);
  23         MonoExceptionClause *clause;
  24         MonoClass *exclass;
  25         int i;
  26
  27         if (!(cfg->opt & MONO_OPT_EXCEPTION))
  28                 return NULL;
  29
  30         if (bb->region == -1 || !MONO_BBLOCK_IS_IN_REGION (bb, MONO_REGION_TRY))
  31                 return NULL;
  32
  33         exclass = mono_class_from_name (mono_get_corlib (), "System", exname);
  34         /* search for the handler */
  35         for (i = 0; i < header->num_clauses; ++i) {
  36                 clause = &header->clauses [i];
  37                 if (MONO_OFFSET_IN_CLAUSE (clause, bb->real_offset)) {
  38                         if (clause->flags == MONO_EXCEPTION_CLAUSE_NONE && clause->data.catch_class && mono_class_is_assignable_from (clause->data.catch_class, exclass)) {
  39                                 MonoBasicBlock *tbb;
  40
  41                                 /* get the basic block for the handler and
  42                                  * check if the exception object is used.
  43                                  * Flag is set during method_to_ir due to
  44                                  * pop-op is optmized away in codegen (burg).
  45                                  */
  46                                 tbb = g_hash_table_lookup (cfg->bb_hash, header->code + clause->handler_offset);
  47                                 if (tbb && tbb->flags & BB_EXCEPTION_DEAD_OBJ && !(tbb->flags & BB_EXCEPTION_UNSAFE)) {
  48                                         MonoBasicBlock *targetbb = tbb;
  49                                         gboolean unsafe = FALSE;
  50
  51                                         /* Check if this catch clause is ok to optimize by
  52                                          * looking for the BB_EXCEPTION_UNSAFE in every BB that
  53                                          * belongs to the same region.
  54                                          *
  55                                          * UNSAFE flag is set during method_to_ir (OP_RETHROW)
  56                                          */
  57                                         while (!unsafe && tbb->next_bb && tbb->region == tbb->next_bb->region) {
  58                                                 if (tbb->next_bb->flags & BB_EXCEPTION_UNSAFE)  {
  59                                                         unsafe = TRUE;
  60                                                         break;
  61                                                 }
  62                                                 tbb = tbb->next_bb;
  63                                         }
  64
  65                                         if (!unsafe) {
  66                                                 MonoInst *jump;
  67
  68                                                 /* Create dummy inst to allow easier integration in
  69                                                  * arch dependent code (opcode ignored)
  70                                                  */
  71                                                 MONO_INST_NEW (cfg, jump, CEE_BR);
  72
  73                                                 /* Allocate memory for our branch target */
  74                                                 jump->inst_i1 = mono_mempool_alloc0 (cfg->mempool, sizeof (MonoInst));
  75                                                 jump->inst_true_bb = targetbb;
  76
  77                                                 if (cfg->verbose_level > 2)
  78                                                         g_print ("found exception to optimize - returning branch to BB%d (%s) (instead of throw) for method %s:%s\n", targetbb->block_num, clause->data.catch_class->name, cfg->method->klass->name, cfg->method->name);
  79
  80                                                 return jump;
  81                                         }
  82
  83                                         return NULL;
  84                                 }
  85                         } else {
  86                                 /* Branching to an outer clause could skip inner clauses */
  87                                 return NULL;
  88                         }
  89                 }
  90         }
  91
  92         return NULL;
  93 }
  94