[PATCH] Improve backwards threader debugging dumps.

[PATCH] Improve backwards threader debugging dumps.

[Aldy Hernandez]

This patch adds debugging helpers to the backwards threader.  I have
also noticed that profitable_path_p() can bail early on paths that
crosses loops and leave the dump of blocks incomplete.  Fixed as
well.

Unfortunately the new methods cannot be marked const, because we call
the solver's dump which is not const.  I believe this was because the
ranger dump calls m_cache.block_range().  This could probably use a
cleanup at a later time.

Tested on x86-64 Linux.

OK?

gcc/ChangeLog:

	* tree-ssa-threadbackward.c (back_threader::dump): New.
	(back_threader::debug): New.
	(back_threader_profitability::profitable_path_p): Dump blocks
	even if we are bailing early.
---
 gcc/tree-ssa-threadbackward.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c
index 3aad1493c4d..b9a0d9a60ad 100644
--- a/gcc/tree-ssa-threadbackward.c
+++ b/gcc/tree-ssa-threadbackward.c
@@ -42,6 +42,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-range-path.h"
 #include "ssa.h"
 #include "tree-cfgcleanup.h"
+#include "tree-pretty-print.h"
 
 // Path registry for the backwards threader.  After all paths have been
 // registered with register_path(), thread_through_all_blocks() is called
@@ -89,6 +90,8 @@ private:
   edge find_taken_edge (const vec<basic_block> &path);
   edge find_taken_edge_cond (const vec<basic_block> &path, gcond *);
   edge find_taken_edge_switch (const vec<basic_block> &path, gswitch *);
+  virtual void debug ();
+  virtual void dump (FILE *out);
 
   back_threader_registry m_registry;
   back_threader_profitability m_profit;
@@ -519,6 +522,30 @@ debug (const vec <basic_block> &path)
   dump_path (stderr, path);
 }
 
+void
+back_threader::dump (FILE *out)
+{
+  m_solver.dump (out);
+  fprintf (out, "\nCandidates for pre-computation:\n");
+  fprintf (out, "===================================\n");
+
+  bitmap_iterator bi;
+  unsigned i;
+
+  EXECUTE_IF_SET_IN_BITMAP (m_imports, 0, i, bi)
+    {
+      tree name = ssa_name (i);
+      print_generic_expr (out, name, TDF_NONE);
+      fprintf (out, "\n");
+    }
+}
+
+void
+back_threader::debug ()
+{
+  dump (stderr);
+}
+
 back_threader_registry::back_threader_registry (int max_allowable_paths)
   : m_max_allowable_paths (max_allowable_paths)
 {
@@ -607,6 +634,14 @@ back_threader_profitability::profitable_path_p (const vec<basic_block> &m_path,
 	  if (bb->loop_father != loop)
 	    {
 	      path_crosses_loops = true;
+
+	      // Dump rest of blocks.
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		for (j++; j < m_path.length (); j++)
+		  {
+		    bb = m_path[j];
+		    fprintf (dump_file, " bb:%i", bb->index);
+		  }
 	      break;
 	    }
 
-- 
2.31.1

[PATCH] Abstract PHI and forwarder block checks in jump threader.

[Aldy Hernandez]

This patch abstracts out a couple common idioms in the forward
threader that I found useful while navigating the code base.

Tested on x86-64 Linux.

OK?

gcc/ChangeLog:

	* tree-ssa-threadedge.c (has_phis_p): New.
	(forwarder_block_p): New.
	(potentially_threadable_block): Call forwarder_block_p.
	(jump_threader::thread_around_empty_blocks): Call has_phis_p.
	(jump_threader::thread_through_normal_block): Call
	forwarder_block_p.
---
 gcc/tree-ssa-threadedge.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c
index e57f6d3e39c..3db54a199fd 100644
--- a/gcc/tree-ssa-threadedge.c
+++ b/gcc/tree-ssa-threadedge.c
@@ -95,6 +95,21 @@ jump_threader::thread_through_all_blocks (bool may_peel_loop_headers)
   return m_registry->thread_through_all_blocks (may_peel_loop_headers);
 }
 
+static inline bool
+has_phis_p (basic_block bb)
+{
+  return !gsi_end_p (gsi_start_phis (bb));
+}
+
+/* Return TRUE for a forwarder block which is defined as having PHIs
+   but no instructions.  */
+
+static bool
+forwarder_block_p (basic_block bb)
+{
+  return gsi_end_p (gsi_start_nondebug_bb (bb)) && has_phis_p (bb);
+}
+
 /* Return TRUE if we may be able to thread an incoming edge into
    BB to an outgoing edge from BB.  Return FALSE otherwise.  */
 
@@ -107,9 +122,8 @@ potentially_threadable_block (basic_block bb)
      not optimized away because they forward from outside a loop
      to the loop header.   We want to thread through them as we can
      sometimes thread to the loop exit, which is obviously profitable.
-     the interesting case here is when the block has PHIs.  */
-  if (gsi_end_p (gsi_start_nondebug_bb (bb))
-      && !gsi_end_p (gsi_start_phis (bb)))
+     The interesting case here is when the block has PHIs.  */
+  if (forwarder_block_p (bb))
     return true;
 
   /* If BB has a single successor or a single predecessor, then
@@ -854,7 +868,7 @@ jump_threader::thread_around_empty_blocks (vec<jump_thread_edge *> *path,
   /* The key property of these blocks is that they need not be duplicated
      when threading.  Thus they cannot have visible side effects such
      as PHI nodes.  */
-  if (!gsi_end_p (gsi_start_phis (bb)))
+  if (has_phis_p (bb))
     return false;
 
   /* Skip over DEBUG statements at the start of the block.  */
@@ -994,8 +1008,7 @@ jump_threader::thread_through_normal_block (vec<jump_thread_edge *> *path,
     {
       /* First case.  The statement simply doesn't have any instructions, but
 	 does have PHIs.  */
-      if (gsi_end_p (gsi_start_nondebug_bb (e->dest))
-	  && !gsi_end_p (gsi_start_phis (e->dest)))
+      if (forwarder_block_p (e->dest))
 	return 0;
 
       /* Second case.  */
-- 
2.31.1

Re: [PATCH] Improve backwards threader debugging dumps.

[Jeff Law]

On 9/3/2021 7:56 AM, Aldy Hernandez wrote:
> This patch adds debugging helpers to the backwards threader.  I have
> also noticed that profitable_path_p() can bail early on paths that
> crosses loops and leave the dump of blocks incomplete.  Fixed as
> well.
>
> Unfortunately the new methods cannot be marked const, because we call
> the solver's dump which is not const.  I believe this was because the
> ranger dump calls m_cache.block_range().  This could probably use a
> cleanup at a later time.
>
> Tested on x86-64 Linux.
>
> OK?
>
> gcc/ChangeLog:
>
> 	* tree-ssa-threadbackward.c (back_threader::dump): New.
> 	(back_threader::debug): New.
> 	(back_threader_profitability::profitable_path_p): Dump blocks
> 	even if we are bailing early.
OK
jeff

Re: [PATCH] Abstract PHI and forwarder block checks in jump threader.

[Jeff Law]

On 9/3/2021 7:56 AM, Aldy Hernandez wrote:
> This patch abstracts out a couple common idioms in the forward
> threader that I found useful while navigating the code base.
>
> Tested on x86-64 Linux.
>
> OK?
>
> gcc/ChangeLog:
>
> 	* tree-ssa-threadedge.c (has_phis_p): New.
> 	(forwarder_block_p): New.
> 	(potentially_threadable_block): Call forwarder_block_p.
> 	(jump_threader::thread_around_empty_blocks): Call has_phis_p.
> 	(jump_threader::thread_through_normal_block): Call
> 	forwarder_block_p.
OK
jeff