[gcc r14-1127] tree-optimization/109849 - missed code hoisting

[gcc r14-1127] tree-optimization/109849 - missed code hoisting

[Richard Biener]

https://gcc.gnu.org/g:9e2017ae6ac788d3e36999bb0f0d20ea0f62c20e

commit r14-1127-g9e2017ae6ac788d3e36999bb0f0d20ea0f62c20e
Author: Richard Biener <rguenther@suse.de>
Date:   Thu May 18 13:52:29 2023 +0200

    tree-optimization/109849 - missed code hoisting
    
    The following fixes code hoisting to properly consider ANTIC_OUT instead
    of ANTIC_IN.  That's a bit expensive to re-compute but since we no
    longer iterate we're doing this only once per BB which should be
    acceptable.  This avoids missing hoistings to the end of blocks where
    something in the block clobbers the hoisted value.
    
            PR tree-optimization/109849
            * tree-ssa-pre.cc (do_hoist_insertion): Compute ANTIC_OUT
            and use that to determine what to hoist.
    
            * gcc.dg/tree-ssa/ssa-hoist-8.c: New testcase.

Diff:
---
 gcc/testsuite/gcc.dg/tree-ssa/ssa-hoist-8.c | 22 +++++++++++++
 gcc/tree-ssa-pre.cc                         | 48 +++++++++++++++++++++++++----
 2 files changed, 64 insertions(+), 6 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-hoist-8.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-hoist-8.c
new file mode 100644
index 00000000000..66bb48e0dc1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-hoist-8.c
@@ -0,0 +1,22 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-pre-stats" } */
+
+int mem;
+void foo ();
+int bar (int flag)
+{
+  int res;
+  foo ();
+  /* Hoist the load of mem here even though foo () clobbers it.  */
+  if (flag)
+    res = mem;
+  else
+    {
+      res = mem;
+      mem = 2;
+    }
+  return res;
+}
+
+/* { dg-final { scan-tree-dump "HOIST inserted: 1" "pre" } } */
+/* { dg-final { scan-tree-dump-times " = mem;" 1 "pre" } } */
diff --git a/gcc/tree-ssa-pre.cc b/gcc/tree-ssa-pre.cc
index 1f7eea93c16..d56431b4145 100644
--- a/gcc/tree-ssa-pre.cc
+++ b/gcc/tree-ssa-pre.cc
@@ -3622,19 +3622,51 @@ do_hoist_insertion (basic_block block)
       && stmt_ends_bb_p (gsi_stmt (last)))
     return false;
 
-  /* Compute the set of hoistable expressions from ANTIC_IN.  First compute
+  /* We have multiple successors, compute ANTIC_OUT by taking the intersection
+     of all of ANTIC_IN translating through PHI nodes.  Note we do not have to
+     worry about iteration stability here so just intersect the expression sets
+     as well.  This is a simplification of what we do in compute_antic_aux.  */
+  bitmap_set_t ANTIC_OUT = bitmap_set_new ();
+  bool first = true;
+  FOR_EACH_EDGE (e, ei, block->succs)
+    {
+      if (first)
+	{
+	  phi_translate_set (ANTIC_OUT, ANTIC_IN (e->dest), e);
+	  first = false;
+	}
+      else if (!gimple_seq_empty_p (phi_nodes (e->dest)))
+	{
+	  bitmap_set_t tmp = bitmap_set_new ();
+	  phi_translate_set (tmp, ANTIC_IN (e->dest), e);
+	  bitmap_and_into (&ANTIC_OUT->values, &tmp->values);
+	  bitmap_and_into (&ANTIC_OUT->expressions, &tmp->expressions);
+	  bitmap_set_free (tmp);
+	}
+      else
+	{
+	  bitmap_and_into (&ANTIC_OUT->values, &ANTIC_IN (e->dest)->values);
+	  bitmap_and_into (&ANTIC_OUT->expressions,
+			   &ANTIC_IN (e->dest)->expressions);
+	}
+    }
+
+  /* Compute the set of hoistable expressions from ANTIC_OUT.  First compute
      hoistable values.  */
   bitmap_set hoistable_set;
 
-  /* A hoistable value must be in ANTIC_IN(block)
+  /* A hoistable value must be in ANTIC_OUT(block)
      but not in AVAIL_OUT(BLOCK).  */
   bitmap_initialize (&hoistable_set.values, &grand_bitmap_obstack);
   bitmap_and_compl (&hoistable_set.values,
-		    &ANTIC_IN (block)->values, &AVAIL_OUT (block)->values);
+		    &ANTIC_OUT->values, &AVAIL_OUT (block)->values);
 
   /* Short-cut for a common case: hoistable_set is empty.  */
   if (bitmap_empty_p (&hoistable_set.values))
-    return false;
+    {
+      bitmap_set_free (ANTIC_OUT);
+      return false;
+    }
 
   /* Compute which of the hoistable values is in AVAIL_OUT of
      at least one of the successors of BLOCK.  */
@@ -3652,11 +3684,14 @@ do_hoist_insertion (basic_block block)
 
   /* Short-cut for a common case: availout_in_some is empty.  */
   if (bitmap_empty_p (&availout_in_some))
-    return false;
+    {
+      bitmap_set_free (ANTIC_OUT);
+      return false;
+    }
 
   /* Hack hoitable_set in-place so we can use sorted_array_from_bitmap_set.  */
   bitmap_move (&hoistable_set.values, &availout_in_some);
-  hoistable_set.expressions = ANTIC_IN (block)->expressions;
+  hoistable_set.expressions = ANTIC_OUT->expressions;
 
   /* Now finally construct the topological-ordered expression set.  */
   vec<pre_expr> exprs = sorted_array_from_bitmap_set (&hoistable_set);
@@ -3731,6 +3766,7 @@ do_hoist_insertion (basic_block block)
     }
 
   exprs.release ();
+  bitmap_set_free (ANTIC_OUT);
 
   return new_stuff;
 }