Add more details to hot/cold partitioning comments and documentation.

2004-08-25  Caroline Tice  <ctice@apple.com>

        * bb-reorder.c (partition_hot_cold_basic_blocks):  Add more details
        to comments at start of function.
        * cfgbuild.c (make_edges):  Add more details to hot/cold partitioning
        comment.
        * cfgcleanup.c (try_simplify_condjump, try_forward_edges,
        merge_blocks_move_predecessor_nojumps,
        merge_blocks_move_successor_nojumps, merge_blocks_move,
        try_crossjump_to_edge, try_crossjump_bb): Likewise.
        * cfglayout.c (fixup_reorder_chain): Likewise.
        * cfgrtl.c (rtl_can_merge_blocks, try_redirect_by_replacing_jump,
        cfg_layout_can_merge_blocks_p):  Likewise.
        * ifcvt.c (find_if_case_1, find_if_case_2): Likewise.
        * passes.c (rest_of_compilation): Update comments for calling
        optimization that partitions hot/cold basic blocks.
        * doc/invoke.texi:  Update documentation of
        freorder-blocks-and-partition flag.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@86570 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 57 insertions, 8 deletions

diff --git a/gcc/cfgcleanup.c b/gcc/cfgcleanup.c
index 22821f3a4e6..91412cf84d5 100644
--- a/gcc/cfgcleanup.c
+++ b/gcc/cfgcleanup.c
@@ -150,7 +150,13 @@ try_simplify_condjump (basic_block cbranch_block)
 
   /* If we are partitioning hot/cold basic blocks, we don't want to
      mess up unconditional or indirect jumps that cross between hot
-     and cold sections.  */
+     and cold sections. 
+
+     Basic block partitioning may result in some jumps that appear to
+     be optimizable (or blocks that appear to be mergeable), but which really 
+     must be left untouched (they are required to make it safely across 
+     partition boundaries).  See the comments at the top of 
+     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */
 
   if (flag_reorder_blocks_and_partition
       && (BB_PARTITION (jump_block) != BB_PARTITION (jump_dest_block)
@@ -419,8 +425,14 @@ try_forward_edges (int mode, basic_block b)
 
   /* If we are partitioning hot/cold basic blocks, we don't want to
      mess up unconditional or indirect jumps that cross between hot
-     and cold sections.  */
+     and cold sections. 
   
+     Basic block partitioning may result in some jumps that appear to
+     be optimizable (or blocks that appear to be mergeable), but which really m
+     ust be left untouched (they are required to make it safely across 
+     partition boundaries).  See the comments at the top of 
+     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */
+
   if (flag_reorder_blocks_and_partition
       && find_reg_note (BB_END (b), REG_CROSSING_JUMP, NULL_RTX))
     return false;
@@ -447,7 +459,14 @@ try_forward_edges (int mode, basic_block b)
       counter = 0;
 
       /* If we are partitioning hot/cold basic_blocks, we don't want to mess
-	 up jumps that cross between hot/cold sections.  */
+	 up jumps that cross between hot/cold sections.
+
+	 Basic block partitioning may result in some jumps that appear
+	 to be optimizable (or blocks that appear to be mergeable), but which 
+	 really must be left untouched (they are required to make it safely 
+	 across partition boundaries).  See the comments at the top of
+	 bb-reorder.c:partition_hot_cold_basic_blocks for complete
+	 details.  */
 
       if (flag_reorder_blocks_and_partition
 	  && first != EXIT_BLOCK_PTR
@@ -670,8 +689,14 @@ merge_blocks_move_predecessor_nojumps (basic_block a, basic_block b)
 
   /* If we are partitioning hot/cold basic blocks, we don't want to
      mess up unconditional or indirect jumps that cross between hot
-     and cold sections.  */
+     and cold sections.
   
+     Basic block partitioning may result in some jumps that appear to
+     be optimizable (or blocks that appear to be mergeable), but which really 
+     must be left untouched (they are required to make it safely across 
+     partition boundaries).  See the comments at the top of 
+     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */
+
   if (flag_reorder_blocks_and_partition
       && (BB_PARTITION (a) != BB_PARTITION (b)
 	  || find_reg_note (BB_END (a), REG_CROSSING_JUMP, NULL_RTX)))
@@ -722,8 +747,14 @@ merge_blocks_move_successor_nojumps (basic_block a, basic_block b)
 
   /* If we are partitioning hot/cold basic blocks, we don't want to
      mess up unconditional or indirect jumps that cross between hot
-     and cold sections.  */
+     and cold sections. 
   
+     Basic block partitioning may result in some jumps that appear to
+     be optimizable (or blocks that appear to be mergeable), but which really 
+     must be left untouched (they are required to make it safely across 
+     partition boundaries).  See the comments at the top of 
+     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */
+
   if (flag_reorder_blocks_and_partition
       && (find_reg_note (BB_END (a), REG_CROSSING_JUMP, NULL_RTX)
 	  || BB_PARTITION (a) != BB_PARTITION (b)))
@@ -787,8 +818,14 @@ merge_blocks_move (edge e, basic_block b, basic_block c, int mode)
 
   /* If we are partitioning hot/cold basic blocks, we don't want to
      mess up unconditional or indirect jumps that cross between hot
-     and cold sections.  */
+     and cold sections. 
   
+     Basic block partitioning may result in some jumps that appear to
+     be optimizable (or blocks that appear to be mergeable), but which really 
+     must be left untouched (they are required to make it safely across 
+     partition boundaries).  See the comments at the top of 
+     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */
+
   if (flag_reorder_blocks_and_partition
       && (find_reg_note (BB_END (b), REG_CROSSING_JUMP, NULL_RTX)
 	  || find_reg_note (BB_END (c), REG_CROSSING_JUMP, NULL_RTX)
@@ -1471,7 +1508,13 @@ try_crossjump_to_edge (int mode, edge e1, edge e2)
   newpos1 = newpos2 = NULL_RTX;
 
   /* If we have partitioned hot/cold basic blocks, it is a bad idea
-     to try this optimization.  */
+     to try this optimization. 
+
+     Basic block partitioning may result in some jumps that appear to
+     be optimizable (or blocks that appear to be mergeable), but which really 
+     must be left untouched (they are required to make it safely across 
+     partition boundaries).  See the comments at the top of 
+     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */
 
   if (flag_reorder_blocks_and_partition && no_new_pseudos)
     return false;
@@ -1670,8 +1713,14 @@ try_crossjump_bb (int mode, basic_block bb)
 
   /* If we are partitioning hot/cold basic blocks, we don't want to
      mess up unconditional or indirect jumps that cross between hot
-     and cold sections.  */
+     and cold sections. 
   
+     Basic block partitioning may result in some jumps that appear to
+     be optimizable (or blocks that appear to be mergeable), but which really 
+     must be left untouched (they are required to make it safely across 
+     partition boundaries).  See the comments at the top of 
+     bb-reorder.c:partition_hot_cold_basic_blocks for complete details.  */
+
   if (flag_reorder_blocks_and_partition
       && (BB_PARTITION (bb->pred->src) != BB_PARTITION (bb->pred->pred_next->src)
 	  || (bb->pred->flags & EDGE_CROSSING)))