df-core.c: Update comments referring to removed features.

2007-12-14  Paolo Bonzini  <bonzini@gnu.org>

	* df-core.c: Update comments referring to removed features.
	* df-problems.c: Likewise.
	* df-scan.c: Likewise.
	* df.h: Likewise.

From-SVN: r130937

gcc/df-core.c

@@ -71,7 +71,7 @@ USAGE:
 
 Here is an example of using the dataflow routines.
 
-      df_[ru,rd,urec,ri,chain]_add_problem (flags);
+      df_[chain,live,note,rd]_add_problem (flags);
 
       df_set_blocks (blocks);
 
@@ -81,7 +81,7 @@ Here is an example of using the dataflow routines.
 
       df_finish_pass (false);
 
-DF_[ru,rd,urec,ri,chain]_ADD_PROBLEM adds a problem, defined by an
+DF_[chain,live,note,rd]_ADD_PROBLEM adds a problem, defined by an
 instance to struct df_problem, to the set of problems solved in this
 instance of df.  All calls to add a problem for a given instance of df
 must occur before the first call to DF_ANALYZE.
@@ -628,9 +628,9 @@ df_remove_problem (struct dataflow *dflow)
 }
 
 
-/* Remove all of the problems that are not permanent.  Scanning, lr,
-   ur and live are permanent, the rest are removable.  Also clear all
-   of the changeable_flags.  */
+/* Remove all of the problems that are not permanent.  Scanning, LR
+   and (at -O2 or higher) LIVE are permanent, the rest are removable.
+   Also clear all of the changeable_flags.  */
 
 void
 df_finish_pass (bool verify ATTRIBUTE_UNUSED)

gcc/df-problems.c

@@ -1304,16 +1304,22 @@ df_lr_verify_transfer_functions (void)
 
 
 /*----------------------------------------------------------------------------
-   COMBINED LIVE REGISTERS AND UNINITIALIZED REGISTERS.
-
-   First find the set of uses for registers that are reachable from
-   the entry block without passing thru a definition.  In and out
-   bitvectors are built for each basic block.  The regnum is used to
-   index into these sets.  See df.h for details.
-
-   Then the in and out sets here are the anded results of the in and
-   out sets from the lr and ur
-   problems. 
+   LIVE AND MUST-INITIALIZED REGISTERS.
+
+   This problem first computes the IN and OUT bitvectors for the
+   must-initialized registers problems, which is a forward problem.
+   It gives the set of registers for which we MUST have an available
+   definition on any path from the entry block to the entry/exit of
+   a basic block.  Sets generate a definition, while clobbers kill
+   a definition.
+
+   In and out bitvectors are built for each basic block and are indexed by
+   regnum (see df.h for details).  In and out bitvectors in struct
+   df_live_bb_info actually refers to the must-initialized problem;
+
+   Then, the in and out sets for the LIVE problem itself are computed.
+   These are the logical AND of the IN and OUT sets from the LR problem
+   and the must-initialized problem. 
 ----------------------------------------------------------------------------*/
 
 /* Private data used to verify the solution for this problem.  */
@@ -1510,7 +1516,7 @@ df_live_init (bitmap all_blocks)
     }
 }
 
-/* Confluence function that ignores fake edges.  */
+/* Forward confluence function that ignores fake edges.  */
 
 static void
 df_live_confluence_n (edge e)
@@ -1525,7 +1531,7 @@ df_live_confluence_n (edge e)
 } 
 
 
-/* Transfer function.  */
+/* Transfer function for the forwards must-initialized problem.  */
 
 static bool
 df_live_transfer_function (int bb_index)
@@ -1540,7 +1546,7 @@ df_live_transfer_function (int bb_index)
 }
 
 
-/* And the LR and UR info to produce the LIVE info.  */
+/* And the LR info with the must-initialized registers, to produce the LIVE info.  */
 
 static void
 df_live_local_finalize (bitmap all_blocks)
@@ -2916,10 +2922,6 @@ static struct df_problem problem_NOTE =
   NULL,                       /* Debugging end block.  */
   NULL,                       /* Incremental solution verify start.  */
   NULL,                       /* Incremental solution verify end.  */
-
-  /* Technically this is only dependent on the live registers problem
-     but it will produce information if built one of uninitialized
-     register problems (UR, UREC) is also run.  */
   &problem_LR,                /* Dependent problem.  */
   TV_DF_NOTE,                 /* Timing variable.  */
   false                       /* Reset blocks on dropping out of blocks_to_analyze.  */

gcc/df-scan.c

@@ -3381,7 +3381,7 @@ df_bb_refs_record (int bb_index, bool scan_insns)
   df_refs_add_to_chains (&collection_rec, bb, NULL);
 
   /* Now that the block has been processed, set the block as dirty so
-     lr and ur will get it processed.  */
+     LR and LIVE will get it processed.  */
   df_set_bb_dirty (bb);
 }
 

gcc/df.h

@@ -36,10 +36,12 @@ struct df_problem;
 struct df_link;
 
 /* Data flow problems.  All problems must have a unique id here.  */ 
+
 /* Scanning is not really a dataflow problem, but it is useful to have
    the basic block functions in the vector so that things get done in
-   a uniform manner.  The first four problems are always defined.  The
-   last 5 are optional and can be added or deleted at any time.  */
+   a uniform manner.  The last four problems can be added or deleted
+   at any time are always defined (though LIVE is always there at -O2
+   or higher); the others are always there.  */
 #define DF_SCAN  0 
 #define DF_LR    1      /* Live Registers backward. */
 #define DF_LIVE  2      /* Live Registers & Uninitialized Registers */