flow.c (find_basic_blocks): During marking phase...

        * flow.c (find_basic_blocks): During marking phase, if we encounter
        an insn with a REG_LABEL note, make the target block live and
        create an edge from the insn to the target block.  Do not make
        edges from all blocks to the target block.

From-SVN: r16469

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index cf2e595..31ead4a 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -5,6 +5,11 @@ Thu Nov 13 12:53:44 1997  Jim Wilson  <wilson@cygnus.com>
 
 Thu Nov 13 11:41:42 1997  Jeffrey A Law  (law@cygnus.com)
 
+       * flow.c (find_basic_blocks): During marking phase, if we encounter
+       an insn with a REG_LABEL note, make the target block live and
+       create an edge from the insn to the target block.  Do not make
+       edges from all blocks to the target block.
+
         * m68k/x-next (OTHER_FIXINCLUDES_DIRS): Include /NextDeveloper/Headers.
 
        * confiugre.in: Tweak NCR entries.

diff --git a/gcc/flow.c b/gcc/flow.c
index d5e777b..ed66ce7 100644 (file)
--- a/gcc/flow.c
+++ b/gcc/flow.c
@@ -378,8 +378,6 @@ find_basic_blocks (f, nonlocal_label_list)
   /* List of label_refs to all labels whose addresses are taken
      and used as data.  */
   rtx label_value_list;
-  /* List of label_refs from REG_LABEL notes.  */
-  rtx reg_label_list;
   rtx x, note, eh_note;
   enum rtx_code prev_code, code;
   int depth, pass;
@@ -389,7 +387,6 @@ find_basic_blocks (f, nonlocal_label_list)
  restart:
 
   label_value_list = 0;
-  reg_label_list = 0;
   block_live_static = block_live;
   bzero (block_live, n_basic_blocks);
   bzero (block_marked, n_basic_blocks);
@@ -553,14 +550,26 @@ find_basic_blocks (f, nonlocal_label_list)
                    if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
                      {
                        
-                       /* We have no idea where the label referenced by this
-                          insn will actually be used.
-
-                          To create an accurate cfg we mark the target blocks
-                          as live and create a list of all the labels
-                          mentioned in REG_LABEL notes.  After we're done
-                          marking blocks, we go back and create an edge from
-                          every live block to labels on the list.  */ 
+                       /* References to labels in non-jumping insns have
+                          REG_LABEL notes attached to them.
+
+                          This can happen for computed gotos; we don't care
+                          about them here since the values are also on the
+                          label_value_list and will be marked live if we find
+                          a live computed goto.
+
+                          This can also happen when we take the address of
+                          a label to pass as an argument to __throw.  Note
+                          throw only uses the value to determine what handler
+                          should be called -- ie the label is not used as
+                          a jump target, it just marks regions in the code.
+
+                          In theory we should be able to ignore the REG_LABEL
+                          notes, but we have to make sure that the label and
+                          associated insns aren't marked dead, so we make
+                          the block in question live and create an edge from
+                          this insn to the label.  This is not strictly
+                          correct, but it is close enough for now.  */
                        for (note = REG_NOTES (insn);
                             note;
                             note = XEXP (note, 1))
@@ -569,9 +578,9 @@ find_basic_blocks (f, nonlocal_label_list)
                              {
                                x = XEXP (note, 0);
                                block_live[BLOCK_NUM (x)] = 1;
-                               reg_label_list
-                                 = gen_rtx (EXPR_LIST, VOIDmode, x,
-                                            reg_label_list);
+                               mark_label_ref (gen_rtx (LABEL_REF,
+                                                        VOIDmode, x),
+                                               insn, 0);
                              }
                          }
 
@@ -632,22 +641,6 @@ find_basic_blocks (f, nonlocal_label_list)
              }
        }
 
-      /* We couldn't determine what edges are needed for labels on the
-        reg_label_list above.  So make an edge from every live block to
-        to every label on the reg_label_list.  */
-      if (reg_label_list)
-       {
-         for (i = 1; i < n_basic_blocks; i++)
-         if (block_live[i])
-           {
-             rtx x;
-
-             for (x = reg_label_list; x; x = XEXP (x, 1))
-               mark_label_ref (gen_rtx (LABEL_REF, VOIDmode, XEXP (x, 0)),
-                               basic_block_end[i], 0);
-           }
-       }
-
       /* This should never happen.  If it does that means we've computed an
         incorrect flow graph, which can lead to aborts/crashes later in the
         compiler or incorrect code generation.