[PATCH] ipa: Self-DCE of uses of removed call LHSs (PR 108007)

[Martin Jambor <mjambor@suse.cz>]

Hi,

PR 108007 is another manifestation where we rely on DCE to clean-up
after IPA-SRA and if the user explicitely switches DCE off, IPA-SRA
can leave behind statements which are fed uninitialized values and
trap, even though their results are themselves never used.

I have already fixed this for unused parameters in callees, this bug
shows that almost the same thing can happen for removed returns, on
the side of callers.  This means that the issue has to be fixed
elsewhere, in call redirection.  This patch adds a function which
recursivewly looks for uses of operations fed specific SSA names and
removes them all.

That would have been easy if it wasn't for debug statements during
tree-inline (from which call redirection is also invoked).  Debug
statements are decoupled from the rest at this point and iterating
over uses of SSAs does not bring them up.  During tree-inline they are
handled especially at the end, I assume in order to make sure that
relative ordering of UIDs are the same with and without debug info.

This means that during tree-inline we need to make a hash of killed
SSAs, that we already have in copy_body_data, available to the
function making the purging.  So the patch duly does also that, making
the interface slightly ugly.

Bootstrapped and tested on x86_64-linux.  OK for master?  (I am not sure
the problem is grave enough to warrant backporting to release branches
but can do that as well if people think I should.)

Thanks,

Martin


gcc/ChangeLog:

2023-05-11  Martin Jambor  <mjambor@suse.cz>

	PR ipa/108007
	* cgraph.h (cgraph_edge): Add a parameter to
	redirect_call_stmt_to_callee.
	* ipa-param-manipulation.h (ipa_param_adjustments): Added a
	parameter to modify_call.
	* cgraph.cc (cgraph_edge::redirect_call_stmt_to_callee): New
	parameter killed_ssas, pass it to padjs->modify_call.
	* ipa-param-manipulation.cc (purge_transitive_uses): New function.
	(ipa_param_adjustments::modify_call): New parameter killed_ssas.
	Instead of substitutin uses, invoke purge_transitive_uses.  If
	hash of killed SSAs has not been provided, create a temporary one
	and release SSAs that have been added to it.
	* tree-inline.cc (redirect_all_calls): Create
	id->killed_new_ssa_names earlier, pass it to edge redirection,
	adjust a comment.
	(copy_body): Release SSAs in id->killed_new_ssa_names.

gcc/testsuite/ChangeLog:

2023-05-11  Martin Jambor  <mjambor@suse.cz>

	PR ipa/108007
	* gcc.dg/ipa/pr108007.c: New test.
---
 gcc/cgraph.cc                       | 10 +++-
 gcc/cgraph.h                        |  9 ++-
 gcc/ipa-param-manipulation.cc       | 85 +++++++++++++++++++++--------
 gcc/ipa-param-manipulation.h        |  3 +-
 gcc/testsuite/gcc.dg/ipa/pr108007.c | 32 +++++++++++
 gcc/tree-inline.cc                  | 28 ++++++----
 6 files changed, 129 insertions(+), 38 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/ipa/pr108007.c

diff --git a/gcc/cgraph.cc b/gcc/cgraph.cc
index e8f9bec8227..5e923bf0557 100644
--- a/gcc/cgraph.cc
+++ b/gcc/cgraph.cc
@@ -1403,11 +1403,17 @@ cgraph_edge::redirect_callee (cgraph_node *n)
    speculative indirect call, remove "speculative" of the indirect call and
    also redirect stmt to it's final direct target.
 
+   When called from within tree-inline, KILLED_SSAs has to contain the pointer
+   to killed_new_ssa_names within the copy_body_data structure and SSAs
+   discovered to be useless (if LHS is removed) will be added to it, otherwise
+   it needs to be NULL.
+
    It is up to caller to iteratively transform each "speculative"
    direct call as appropriate.  */
 
 gimple *
-cgraph_edge::redirect_call_stmt_to_callee (cgraph_edge *e)
+cgraph_edge::redirect_call_stmt_to_callee (cgraph_edge *e,
+					   hash_set <tree> *killed_ssas)
 {
   tree decl = gimple_call_fndecl (e->call_stmt);
   gcall *new_stmt;
@@ -1527,7 +1533,7 @@ cgraph_edge::redirect_call_stmt_to_callee (cgraph_edge *e)
 	remove_stmt_from_eh_lp (e->call_stmt);
 
       tree old_fntype = gimple_call_fntype (e->call_stmt);
-      new_stmt = padjs->modify_call (e, false);
+      new_stmt = padjs->modify_call (e, false, killed_ssas);
       cgraph_node *origin = e->callee;
       while (origin->clone_of)
 	origin = origin->clone_of;
diff --git a/gcc/cgraph.h b/gcc/cgraph.h
index f5f54769eda..c1a3691b6f5 100644
--- a/gcc/cgraph.h
+++ b/gcc/cgraph.h
@@ -1833,9 +1833,16 @@ public:
      speculative indirect call, remove "speculative" of the indirect call and
      also redirect stmt to it's final direct target.
 
+     When called from within tree-inline, KILLED_SSAs has to contain the
+     pointer to killed_new_ssa_names within the copy_body_data structure and
+     SSAs discovered to be useless (if LHS is removed) will be added to it,
+     otherwise it needs to be NULL.
+
      It is up to caller to iteratively transform each "speculative"
      direct call as appropriate.  */
-  static gimple *redirect_call_stmt_to_callee (cgraph_edge *e);
+  static gimple *redirect_call_stmt_to_callee (cgraph_edge *e,
+					       hash_set <tree>
+					       *killed_ssas = nullptr);
 
   /* Create clone of edge in the node N represented
      by CALL_EXPR the callgraph.  */
diff --git a/gcc/ipa-param-manipulation.cc b/gcc/ipa-param-manipulation.cc
index a286af7f5d9..bf2adeb4bd6 100644
--- a/gcc/ipa-param-manipulation.cc
+++ b/gcc/ipa-param-manipulation.cc
@@ -593,14 +593,63 @@ isra_get_ref_base_and_offset (tree expr, tree *base_p, unsigned *unit_offset_p)
   return true;
 }
 
+/* Remove all statements that use NAME and transitively those that use the
+   result of such statements.  KILLED_SSAS contains the SSA_NAMEs that are
+   already being or have been processed and new ones need to be added to it.
+   The funtction only has to process situations handled by
+   ssa_name_only_returned_p in ipa-sra.cc with the exception that it can assume
+   it must never reach a use in a return statement.  */
+
+static void
+purge_transitive_uses (tree name, hash_set <tree> *killed_ssas)
+{
+  imm_use_iterator imm_iter;
+  gimple *stmt;
+
+  FOR_EACH_IMM_USE_STMT (stmt, imm_iter, name)
+    {
+      if (gimple_debug_bind_p (stmt))
+	{
+	  /* When runing within tree-inline, we will never end up here but
+	     adding the SSAs to killed_ssas will do the trick in this case and
+	     the respective debug statements will get reset. */
+
+	  gimple_debug_bind_reset_value (stmt);
+	  update_stmt (stmt);
+	  continue;
+	}
+
+      tree lhs = NULL_TREE;
+      if (is_gimple_assign (stmt))
+	lhs = gimple_assign_lhs (stmt);
+      else if (gimple_code (stmt) == GIMPLE_PHI)
+	lhs = gimple_phi_result (stmt);
+      gcc_assert (lhs
+		  && (TREE_CODE (lhs) == SSA_NAME)
+		  && !gimple_vdef (stmt));
+
+      if (!killed_ssas->contains (lhs))
+	{
+	  killed_ssas->add (lhs);
+	  purge_transitive_uses (lhs, killed_ssas);
+	  gimple_stmt_iterator gsi = gsi_for_stmt (stmt);
+	  gsi_remove (&gsi, true);
+	}
+    }
+}
+
 /* Modify actual arguments of a function call in statement currently belonging
    to CS, and make it call CS->callee->decl.  Return the new statement that
    replaced the old one.  When invoked, cfun and current_function_decl have to
-   be set to the caller.  */
+   be set to the caller.  When called from within tree-inline, KILLED_SSAs has
+   to contain the pointer to killed_new_ssa_names within the copy_body_data
+   structure and SSAs discovered to be useless (if LHS is removed) will be
+   added to it, otherwise it needs to be NULL.  */
 
 gcall *
 ipa_param_adjustments::modify_call (cgraph_edge *cs,
-				    bool update_references)
+				    bool update_references,
+				    hash_set <tree> *killed_ssas)
 {
   gcall *stmt = cs->call_stmt;
   tree callee_decl = cs->callee->decl;
@@ -910,32 +959,20 @@ ipa_param_adjustments::modify_call (cgraph_edge *cs,
 
   gcall *new_stmt = gimple_build_call_vec (callee_decl, vargs);
 
-  tree ssa_to_remove = NULL;
+  hash_set <tree> *ssas_to_remove = NULL;
   if (tree lhs = gimple_call_lhs (stmt))
     {
       if (!m_skip_return)
 	gimple_call_set_lhs (new_stmt, lhs);
       else if (TREE_CODE (lhs) == SSA_NAME)
 	{
-	  /* LHS should now by a default-def SSA.  Unfortunately default-def
-	     SSA_NAMEs need a backing variable (or at least some code examining
-	     SSAs assumes it is non-NULL).  So we either have to re-use the
-	     decl we have at hand or introdice a new one.  */
-	  tree repl = create_tmp_var (TREE_TYPE (lhs), "removed_return");
-	  repl = get_or_create_ssa_default_def (cfun, repl);
-	  SSA_NAME_IS_DEFAULT_DEF (repl) = true;
-	  imm_use_iterator ui;
-	  use_operand_p use_p;
-	  gimple *using_stmt;
-	  FOR_EACH_IMM_USE_STMT (using_stmt, ui, lhs)
+	  if (!killed_ssas)
 	    {
-	      FOR_EACH_IMM_USE_ON_STMT (use_p, ui)
-		{
-		  SET_USE (use_p, repl);
-		}
-	      update_stmt (using_stmt);
+	      ssas_to_remove = new hash_set<tree> (8);
+	      killed_ssas = ssas_to_remove;
 	    }
-	  ssa_to_remove = lhs;
+	  killed_ssas->add (lhs);
+	  purge_transitive_uses (lhs, killed_ssas);
 	}
     }
 
@@ -954,8 +991,12 @@ ipa_param_adjustments::modify_call (cgraph_edge *cs,
       fprintf (dump_file, "\n");
     }
   gsi_replace (&gsi, new_stmt, true);
-  if (ssa_to_remove)
-    release_ssa_name (ssa_to_remove);
+  if (ssas_to_remove)
+    {
+      for (tree sn : *ssas_to_remove)
+	release_ssa_name (sn);
+      delete ssas_to_remove;
+    }
   if (update_references)
     do
       {
diff --git a/gcc/ipa-param-manipulation.h b/gcc/ipa-param-manipulation.h
index 9798eedf0b6..5b2f90f8307 100644
--- a/gcc/ipa-param-manipulation.h
+++ b/gcc/ipa-param-manipulation.h
@@ -224,7 +224,8 @@ public:
 
   /* Modify a call statement arguments (and possibly remove the return value)
      as described in the data fields of this class.  */
-  gcall *modify_call (cgraph_edge *cs, bool update_references);
+  gcall *modify_call (cgraph_edge *cs, bool update_references,
+		      hash_set <tree> *killed_ssas);
   /* Return if the first parameter is left intact.  */
   bool first_param_intact_p ();
   /* Build a function type corresponding to the modified call.  */
diff --git a/gcc/testsuite/gcc.dg/ipa/pr108007.c b/gcc/testsuite/gcc.dg/ipa/pr108007.c
new file mode 100644
index 00000000000..77fc95975cf
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/pr108007.c
@@ -0,0 +1,32 @@
+/* { dg-do run } */
+/* { dg-options "-Os -fno-dce -fno-tree-dce -g" } */
+
+/* This tests that when IPA-SRA removes a LHS of a call statement which, in the
+   original source, is fed into a useless operation which however can trap when
+   given nonsensical input, that we remove it even when the user has turned off
+   normal DCE.  */
+
+int a, b, d, e, f = 10000000, h;
+short c, g;
+static int *i() {
+  g = f;
+ L:
+  h = e = ~g;
+  g = ~f % g & e;
+  if (!g)
+    goto L;
+  c++;
+  while (g < 1)
+    ;
+  return &a;
+}
+static void k() {
+  int *l, m = 2;
+  l = i();
+  for (; d < 1; d++)
+    m |= *l >= b;
+}
+int main() {
+  k();
+  return 0;
+}
diff --git a/gcc/tree-inline.cc b/gcc/tree-inline.cc
index 63a19f8d1d8..1c20e9545d1 100644
--- a/gcc/tree-inline.cc
+++ b/gcc/tree-inline.cc
@@ -2982,20 +2982,19 @@ redirect_all_calls (copy_body_data * id, basic_block bb)
 	  struct cgraph_edge *edge = id->dst_node->get_edge (stmt);
 	  if (edge)
 	    {
+	      if (!id->killed_new_ssa_names)
+		id->killed_new_ssa_names = new hash_set<tree> (16);
 	      gimple *new_stmt
-		= cgraph_edge::redirect_call_stmt_to_callee (edge);
-	      /* If IPA-SRA transformation, run as part of edge redirection,
-		 removed the LHS because it is unused, save it to
-		 killed_new_ssa_names so that we can prune it from debug
-		 statements.  */
+		= cgraph_edge::redirect_call_stmt_to_callee (edge,
+		    id->killed_new_ssa_names);
 	      if (old_lhs
 		  && TREE_CODE (old_lhs) == SSA_NAME
 		  && !gimple_call_lhs (new_stmt))
-		{
-		  if (!id->killed_new_ssa_names)
-		    id->killed_new_ssa_names = new hash_set<tree> (16);
-		  id->killed_new_ssa_names->add (old_lhs);
-		}
+		/* In case of IPA-SRA removing the LHS, the name should have
+		   been already added to the hash.  But in case of redirecting
+		   to builtin_unreachable it was not and the name still should
+		   be pruned from debug statements.  */
+		id->killed_new_ssa_names->add (old_lhs);
 
 	      if (stmt == last && id->call_stmt && maybe_clean_eh_stmt (stmt))
 		gimple_purge_dead_eh_edges (bb);
@@ -3322,8 +3321,13 @@ copy_body (copy_body_data *id,
   body = copy_cfg_body (id, entry_block_map, exit_block_map,
 			new_entry);
   copy_debug_stmts (id);
-  delete id->killed_new_ssa_names;
-  id->killed_new_ssa_names = NULL;
+  if (id->killed_new_ssa_names)
+    {
+      for (tree sn : *id->killed_new_ssa_names)
+	release_ssa_name (sn);
+      delete id->killed_new_ssa_names;
+      id->killed_new_ssa_names = NULL;
+    }
 
   return body;
 }
-- 
2.40.0