[PATCH] DWARF: turn dw_loc_descr_node field into hash map for frame offset check

[Pierre-Marie de Rodat <derodat at adacore dot com>]

Hello,

As discussed on
<https://gcc.gnu.org/ml/gcc-patches/2016-02/msg01708.html>, this change
removes a field in the dw_loc_descr_node structure so we can get rid of
the CHECKING_P macro usage.

This field was used to perform consistency checks for frame offset in
DWARF procedures. As a replacement, this commit turns the "visited
nodes" set in resolve_args_picking_1 into a map that remembers for each
dw_loc_descr_node the frame offset associated to it, so that the
consistency check is still operational.

Boostrapped and regtested on x86_64-linux. Ok to commit? Thank you in
advance!
---
 gcc/dwarf2out.c | 37 +++++++++++++++++++------------------
 gcc/dwarf2out.h |  6 ------
 2 files changed, 19 insertions(+), 24 deletions(-)

diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 0bbff87..463863d 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -1325,9 +1325,6 @@ new_loc_descr (enum dwarf_location_atom op, unsigned HOST_WIDE_INT oprnd1,
   dw_loc_descr_ref descr = ggc_cleared_alloc<dw_loc_descr_node> ();
 
   descr->dw_loc_opc = op;
-#if CHECKING_P
-  descr->dw_loc_frame_offset = -1;
-#endif
   descr->dw_loc_oprnd1.val_class = dw_val_class_unsigned_const;
   descr->dw_loc_oprnd1.val_entry = NULL;
   descr->dw_loc_oprnd1.v.val_unsigned = oprnd1;
@@ -15353,12 +15350,14 @@ is_handled_procedure_type (tree type)
 	  && int_size_in_bytes (type) <= DWARF2_ADDR_SIZE);
 }
 
-/* Helper for resolve_args_picking.  Stop when coming across VISITED nodes.  */
+/* Helper for resolve_args_picking: do the same but stop when coming across
+   visited nodes.  For each node we visit, register in FRAME_OFFSETS the frame
+   offset *before* evaluating the corresponding operation.  */
 
 static bool
 resolve_args_picking_1 (dw_loc_descr_ref loc, unsigned initial_frame_offset,
 			struct dwarf_procedure_info *dpi,
-			hash_set<dw_loc_descr_ref> &visited)
+			hash_map<dw_loc_descr_ref, unsigned> &frame_offsets)
 {
   /* The "frame_offset" identifier is already used to name a macro... */
   unsigned frame_offset_ = initial_frame_offset;
@@ -15366,19 +15365,18 @@ resolve_args_picking_1 (dw_loc_descr_ref loc, unsigned initial_frame_offset,
 
   for (l = loc; l != NULL;)
     {
+      bool existed;
+      unsigned &l_frame_offset = frame_offsets.get_or_insert (l, &existed);
+
       /* If we already met this node, there is nothing to compute anymore.  */
-      if (visited.add (l))
+      if (existed)
 	{
-#if CHECKING_P
 	  /* Make sure that the stack size is consistent wherever the execution
 	     flow comes from.  */
-	  gcc_assert ((unsigned) l->dw_loc_frame_offset == frame_offset_);
-#endif
+	  gcc_assert ((unsigned) l_frame_offset == frame_offset_);
 	  break;
 	}
-#if CHECKING_P
-      l->dw_loc_frame_offset = frame_offset_;
-#endif
+      l_frame_offset = frame_offset_;
 
       /* If needed, relocate the picking offset with respect to the frame
 	 offset. */
@@ -15601,7 +15599,7 @@ resolve_args_picking_1 (dw_loc_descr_ref loc, unsigned initial_frame_offset,
 	{
 	case DW_OP_bra:
 	  if (!resolve_args_picking_1 (l->dw_loc_next, frame_offset_, dpi,
-				       visited))
+				       frame_offsets))
 	    return false;
 	  /* Fall through... */
 
@@ -15623,17 +15621,20 @@ resolve_args_picking_1 (dw_loc_descr_ref loc, unsigned initial_frame_offset,
 
 /* Make a DFS over operations reachable through LOC (i.e. follow branch
    operations) in order to resolve the operand of DW_OP_pick operations that
-   target DWARF procedure arguments (DPI).  Stop at already visited nodes.
-   INITIAL_FRAME_OFFSET is the frame offset *before* LOC is executed.  Return
-   if all relocations were successful.  */
+   target DWARF procedure arguments (DPI).  INITIAL_FRAME_OFFSET is the frame
+   offset *before* LOC is executed.  Return if all relocations were
+   successful.  */
 
 static bool
 resolve_args_picking (dw_loc_descr_ref loc, unsigned initial_frame_offset,
 		      struct dwarf_procedure_info *dpi)
 {
-  hash_set<dw_loc_descr_ref> visited;
+  /* Associate to all visited operations the frame offset *before* evaluating
+     this operation.  */
+  hash_map<dw_loc_descr_ref, unsigned> frame_offsets;
 
-  return resolve_args_picking_1 (loc, initial_frame_offset, dpi, visited);
+  return resolve_args_picking_1 (loc, initial_frame_offset, dpi,
+				 frame_offsets);
 }
 
 /* Try to generate a DWARF procedure that computes the same result as FNDECL.
diff --git a/gcc/dwarf2out.h b/gcc/dwarf2out.h
index 91b3d6b..abf0550 100644
--- a/gcc/dwarf2out.h
+++ b/gcc/dwarf2out.h
@@ -239,12 +239,6 @@ struct GTY((chain_next ("%h.dw_loc_next"))) dw_loc_descr_node {
      frame offset.  */
   unsigned int frame_offset_rel : 1;
   int dw_loc_addr;
-#if CHECKING_P
-  /* When translating a function into a DWARF procedure, contains the frame
-     offset *before* evaluating this operation.  It is -1 when not yet
-     initialized.  */
-  int dw_loc_frame_offset;
-#endif
   dw_val_node dw_loc_oprnd1;
   dw_val_node dw_loc_oprnd2;
 };
-- 
2.7.4