[gcc r14-4382] ipa: Self-DCE of uses of removed call LHSs (PR 108007)

[gcc r14-4382] ipa: Self-DCE of uses of removed call LHSs (PR 108007)

[Martin Jambor]

https://gcc.gnu.org/g:1be18ea110a2d69570dbc494588a7c73173883be

commit r14-4382-g1be18ea110a2d69570dbc494588a7c73173883be
Author: Martin Jambor <mjambor@suse.cz>
Date:   Tue Oct 3 18:44:51 2023 +0200

    ipa: Self-DCE of uses of removed call LHSs (PR 108007)
    
    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
    looks for (and through, using a work-list) 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.
    
    gcc/ChangeLog:
    
    2023-09-27  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): Add 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 substituting 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.

Diff:
---
 gcc/cgraph.cc                       | 10 ++++-
 gcc/cgraph.h                        |  9 +++-
 gcc/ipa-param-manipulation.cc       | 88 +++++++++++++++++++++++++++----------
 gcc/ipa-param-manipulation.h        |  3 +-
 gcc/testsuite/gcc.dg/ipa/pr108007.c | 32 ++++++++++++++
 gcc/tree-inline.cc                  | 28 +++++++-----
 6 files changed, 132 insertions(+), 38 deletions(-)

diff --git a/gcc/cgraph.cc b/gcc/cgraph.cc
index e41e5ad3ae7..b82367ac342 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 cedaaac3a45..d7162efeeb4 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 4a185ddbdf4..0c49267ccf8 100644
--- a/gcc/ipa-param-manipulation.cc
+++ b/gcc/ipa-param-manipulation.cc
@@ -593,14 +593,66 @@ 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;
+  auto_vec <tree, 4> worklist;
+
+  worklist.safe_push (name);
+  while (!worklist.is_empty ())
+    {
+      tree cur_name = worklist.pop ();
+      FOR_EACH_IMM_USE_STMT (stmt, imm_iter, cur_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->add (lhs))
+	    {
+	      worklist.safe_push (lhs);
+	      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 +962,20 @@ 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 +994,12 @@ 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 d6a26e9ad36..b7e56fe6379 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 d63060c9429..8daef6955fd 100644
--- a/gcc/tree-inline.cc
+++ b/gcc/tree-inline.cc
@@ -2988,20 +2988,19 @@ 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);
@@ -3328,8 +3327,13 @@ 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;
 }