[PATCH 2/4] ipa-sra: Introduce a mini-DCE to tree-inline.c (PR 93385)

Martin Jambor mjambor@suse.cz
Thu May 28 12:06:36 GMT 2020


PR 93385 reveals that if the user explicitely disables DCE, IPA-SRA
can leave behind statements which are useless because their results
are eventually not used but can have problematic side effects,
especially since their inputs are now bogus that useless parameters
were removed.

This patch fixes the problem by doing a similar def-use walk when
materializing clones, marking which statements should not be copied
and which SSA_NAMEs will be removed by call redirections and now need
to be replaced with anything valid.  Default-definition SSA_NAMEs of
parameters which are removed and all SSA_NAMEs derived from them (in a
phi node or a simple assignment statement) are then remapped to
error_mark_node - a sure way to spot it if any is left in place.

There is one exception to the above rule, if such SSA_NAMEs appear as
an argument of a call, they need to be removed by call redirection and
not as part of clone materialization.  So to have something valid
there until that time, this patch pulls out dummy declarations out of
thin air.  If you do not like that, see patch number 4 in the series,
which changes this, but probably in a controversial way.

This patch only resets debug statements using the removed SSA_NAMEs.
The first follow-up patch adjusts debug statements in the current
function to still try to make the removed values available in debugger
in the current function and the subsequent one also in other functions
where they are passed.

gcc/ChangeLog:

2020-05-14  Martin Jambor  <mjambor@suse.cz>

	PR ipa/93385
	* ipa-param-manipulation.h (class ipa_param_body_adjustments): New
	members m_dead_stmts, m_dead_ssas, mark_dead_statements and
	get_removed_call_arg_placeholder.
	* ipa-param-manipulation.c (phi_arg_will_live_p): New function.
	(ipa_param_body_adjustments::mark_dead_statements): New method.
	(ipa_param_body_adjustments::common_initialization): Call it.
	(ipa_param_body_adjustments::ipa_param_body_adjustments): Initialize
	new mwmbers.
	(ipa_param_body_adjustments::get_removed_call_arg_placeholder): New.
	(ipa_param_body_adjustments::modify_call_stmt): Replace dead SSAs
	with dummy decls.
	* tree-inline.c (remap_gimple_stmt): Do not copy dead statements,
	reset dead debug statements.
	(copy_phis_for_bb): Do not copy dead PHI nodes.

gcc/testsuite/ChangeLog:

2020-05-14  Martin Jambor  <mjambor@suse.cz>

	PR ipa/93385
	* gcc.dg/ipa/pr93385.c: New test.
	* gcc.dg/ipa/ipa-sra-23.c: Likewise.
---
 gcc/ipa-param-manipulation.c          | 142 ++++++++++++++++++++++++--
 gcc/ipa-param-manipulation.h          |   8 ++
 gcc/testsuite/gcc.dg/ipa/ipa-sra-23.c |  24 +++++
 gcc/testsuite/gcc.dg/ipa/pr93385.c    |  27 +++++
 gcc/tree-inline.c                     |  18 +++-
 5 files changed, 205 insertions(+), 14 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/ipa/ipa-sra-23.c
 create mode 100644 gcc/testsuite/gcc.dg/ipa/pr93385.c

diff --git a/gcc/ipa-param-manipulation.c b/gcc/ipa-param-manipulation.c
index 978916057f0..1f47f3a4268 100644
--- a/gcc/ipa-param-manipulation.c
+++ b/gcc/ipa-param-manipulation.c
@@ -953,6 +953,99 @@ ipa_param_body_adjustments::carry_over_param (tree t)
   return new_parm;
 }
 
+/* Return true if BLOCKS_TO_COPY is NULL or if PHI has an argument ARG in
+   position that corresponds to an edge that is coming from a block that has
+   the corresponding bit set in BLOCKS_TO_COPY.  */
+
+static bool
+phi_arg_will_live_p (gphi *phi, bitmap blocks_to_copy, tree arg)
+{
+  bool arg_will_survive = false;
+  if (!blocks_to_copy)
+    arg_will_survive = true;
+  else
+    for (unsigned i = 0; i < gimple_phi_num_args (phi); i++)
+      if (gimple_phi_arg_def (phi, i) == arg
+	  && bitmap_bit_p (blocks_to_copy,
+			   gimple_phi_arg_edge (phi, i)->src->index))
+	{
+	  arg_will_survive = true;
+	  break;
+	}
+  return arg_will_survive;
+}
+
+/* Populate m_dead_stmts given that DEAD_PARAM is going to be removed without
+   any replacement or splitting.  */
+
+void
+ipa_param_body_adjustments::mark_dead_statements (tree dead_param)
+{
+  if (!is_gimple_reg (dead_param))
+    return;
+  tree parm_ddef = ssa_default_def (m_id->src_cfun, dead_param);
+  if (!parm_ddef || has_zero_uses (parm_ddef))
+    return;
+
+  auto_vec<tree, 4> stack;
+  m_dead_ssas.add (parm_ddef);
+  stack.safe_push (parm_ddef);
+  while (!stack.is_empty ())
+    {
+      tree t = stack.pop ();
+
+      imm_use_iterator imm_iter;
+      gimple *stmt;
+
+      insert_decl_map (m_id, t, error_mark_node);
+      FOR_EACH_IMM_USE_STMT (stmt, imm_iter, t)
+	{
+	  if (is_gimple_call (stmt)
+	      || (m_id->blocks_to_copy
+		  && !bitmap_bit_p (m_id->blocks_to_copy,
+				    gimple_bb (stmt)->index)))
+	    continue;
+
+	  if (is_gimple_debug (stmt))
+	    {
+	      m_dead_stmts.add (stmt);
+	      gcc_assert (gimple_debug_bind_p (stmt));
+	    }
+	  else if (gimple_code (stmt) == GIMPLE_PHI)
+	    {
+	      gphi *phi = as_a <gphi *> (stmt);
+	      if (phi_arg_will_live_p (phi, m_id->blocks_to_copy, t))
+		{
+		  m_dead_stmts.add (phi);
+		  tree res = gimple_phi_result (phi);
+		  if (!m_dead_ssas.contains (res))
+		    {
+		      stack.safe_push (res);
+		      m_dead_ssas.add (res);
+		    }
+		}
+	    }
+	  else if (is_gimple_assign (stmt))
+	    {
+	      m_dead_stmts.add (stmt);
+	      if (!gimple_clobber_p (stmt))
+		{
+		  tree lhs = gimple_assign_lhs (stmt);
+		  gcc_assert (TREE_CODE (lhs) == SSA_NAME);
+		  if (!m_dead_ssas.contains (lhs))
+		    {
+		      m_dead_ssas.add (lhs);
+		      stack.safe_push (lhs);
+		    }
+		}
+	    }
+	  else
+	    /* IPA-SRA does not analyze other types of statements.  */
+	    gcc_unreachable ();
+	}
+    }
+}
+
 /* Common initialization performed by all ipa_param_body_adjustments
    constructors.  OLD_FNDECL is the declaration we take original arguments
    from, (it may be the same as M_FNDECL).  VARS, if non-NULL, is a pointer to
@@ -1095,6 +1188,11 @@ ipa_param_body_adjustments::common_initialization (tree old_fndecl,
 		/* Declare this new variable.  */
 		DECL_CHAIN (var) = *vars;
 		*vars = var;
+
+		/* If this is not a split but a real removal, init hash sets
+		   that will guide what not to copy to the new body.  */
+		if (!isra_dummy_decls[i])
+		  mark_dead_statements (m_oparms[i]);
 	      }
 	  }
 	else
@@ -1151,9 +1249,10 @@ ipa_param_body_adjustments
 ::ipa_param_body_adjustments (vec<ipa_adjusted_param, va_gc> *adj_params,
 			      tree fndecl)
   : m_adj_params (adj_params), m_adjustments (NULL), m_reset_debug_decls (),
-    m_split_modifications_p (false), m_fndecl (fndecl), m_id (NULL),
-    m_oparms (), m_new_decls (), m_new_types (), m_replacements (),
-    m_removed_decls (), m_removed_map (), m_method2func (false)
+    m_split_modifications_p (false), m_dead_stmts (), m_dead_ssas (),
+    m_fndecl (fndecl), m_id (NULL), m_oparms (), m_new_decls (),
+    m_new_types (), m_replacements (), m_removed_decls (), m_removed_map (),
+    m_method2func (false)
 {
   common_initialization (fndecl, NULL, NULL);
 }
@@ -1167,9 +1266,9 @@ ipa_param_body_adjustments
 ::ipa_param_body_adjustments (ipa_param_adjustments *adjustments,
 			      tree fndecl)
   : m_adj_params (adjustments->m_adj_params), m_adjustments (adjustments),
-    m_reset_debug_decls (), m_split_modifications_p (false), m_fndecl (fndecl),
-    m_id (NULL), m_oparms (), m_new_decls (), m_new_types (),
-    m_replacements (), m_removed_decls (), m_removed_map (),
+    m_reset_debug_decls (), m_split_modifications_p (false), m_dead_stmts (),
+    m_dead_ssas (), m_fndecl (fndecl), m_id (NULL), m_oparms (), m_new_decls (),
+    m_new_types (), m_replacements (), m_removed_decls (), m_removed_map (),
     m_method2func (false)
 {
   common_initialization (fndecl, NULL, NULL);
@@ -1190,9 +1289,10 @@ ipa_param_body_adjustments
 			      copy_body_data *id, tree *vars,
 			      vec<ipa_replace_map *, va_gc> *tree_map)
   : m_adj_params (adjustments->m_adj_params), m_adjustments (adjustments),
-    m_reset_debug_decls (), m_split_modifications_p (false), m_fndecl (fndecl),
-    m_id (id), m_oparms (), m_new_decls (), m_new_types (), m_replacements (),
-    m_removed_decls (), m_removed_map (), m_method2func (false)
+    m_reset_debug_decls (), m_split_modifications_p (false), m_dead_stmts (),
+    m_dead_ssas (),m_fndecl (fndecl), m_id (id), m_oparms (), m_new_decls (),
+    m_new_types (), m_replacements (), m_removed_decls (), m_removed_map (),
+    m_method2func (false)
 {
   common_initialization (old_fndecl, vars, tree_map);
 }
@@ -1519,6 +1619,19 @@ remap_split_decl_to_dummy (tree *tp, int *walk_subtrees, void *data)
   return NULL_TREE;
 }
 
+/* Given ARG which is a SSA_NAME call argument which we are however removing
+   from the current function and which will be thus removed from the call
+   statement by ipa_param_adjustments::modify_call, return something that can
+   be used as a placeholder and which the operand scanner will accept until
+   then.  */
+
+tree
+ipa_param_body_adjustments::get_removed_call_arg_placeholder (tree arg)
+{
+  tree t = create_tmp_var (TREE_TYPE (arg));
+  insert_decl_map (m_id, t, t);
+  return t;
+}
 
 /* If the call statement pointed at by STMT_P contains any expressions that
    need to replaced with a different one as noted by ADJUSTMENTS, do so.  f the
@@ -1658,7 +1771,10 @@ ipa_param_body_adjustments::modify_call_stmt (gcall **stmt_p)
 	  else
 	    {
 	      tree t = gimple_call_arg (stmt, i);
-	      modify_expression (&t, true);
+	      if (TREE_CODE (t) == SSA_NAME && m_dead_ssas.contains(t))
+		t = get_removed_call_arg_placeholder (t);
+	      else
+		modify_expression (&t, true);
 	      vargs.safe_push (t);
 	    }
 	}
@@ -1680,7 +1796,11 @@ ipa_param_body_adjustments::modify_call_stmt (gcall **stmt_p)
   for (unsigned i = 0; i < nargs; i++)
     {
       tree *t = gimple_call_arg_ptr (stmt, i);
-      modified |= modify_expression (t, true);
+
+      if (TREE_CODE (*t) == SSA_NAME && m_dead_ssas.contains(*t))
+	*t = get_removed_call_arg_placeholder (*t);
+      else
+	modified |= modify_expression (t, true);
     }
 
   if (gimple_call_lhs (stmt))
diff --git a/gcc/ipa-param-manipulation.h b/gcc/ipa-param-manipulation.h
index 0b038ea57f1..59060ae5dcc 100644
--- a/gcc/ipa-param-manipulation.h
+++ b/gcc/ipa-param-manipulation.h
@@ -370,6 +370,12 @@ public:
   /* Set to true if there are any IPA_PARAM_OP_SPLIT adjustments among stored
      adjustments.  */
   bool m_split_modifications_p;
+
+  /* Sets of statements and SSA_NAMEs that only manipulate data from parameters
+     removed because they are not necessary.  */
+  hash_set<gimple *> m_dead_stmts;
+  hash_set<tree> m_dead_ssas;
+
 private:
   void common_initialization (tree old_fndecl, tree *vars,
 			      vec<ipa_replace_map *, va_gc> *tree_map);
@@ -383,6 +389,8 @@ private:
   bool modify_call_stmt (gcall **stmt_p);
   bool modify_cfun_body ();
   void reset_debug_stmts ();
+  void mark_dead_statements (tree dead_param);
+  tree get_removed_call_arg_placeholder (tree arg);
 
   /* Declaration of the function that is being transformed.  */
 
diff --git a/gcc/testsuite/gcc.dg/ipa/ipa-sra-23.c b/gcc/testsuite/gcc.dg/ipa/ipa-sra-23.c
new file mode 100644
index 00000000000..f438b509614
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/ipa-sra-23.c
@@ -0,0 +1,24 @@
+/* { dg-do compile } */
+/* { dg-options "-O2"  } */
+
+extern int g;
+
+static int __attribute__((noinline))
+bar (int i, int j)
+{
+  return 2*g + i;
+}
+
+static int __attribute__((noinline))
+foo (int i, int j)
+{
+  if (i > 5)
+    j = 22;
+  return bar (i, j) + 1;
+}
+
+int
+entry (int l, int k)
+{
+  return foo (l, k);
+}
diff --git a/gcc/testsuite/gcc.dg/ipa/pr93385.c b/gcc/testsuite/gcc.dg/ipa/pr93385.c
new file mode 100644
index 00000000000..6d1d0d7cd27
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/pr93385.c
@@ -0,0 +1,27 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -fno-dce -fno-ipa-cp -fno-tree-dce" } */
+
+char a, b;
+
+#ifdef __SIZEOF_INT128__
+#define T unsigned __int128
+#else
+#define T unsigned
+#endif
+
+static inline int
+c (T d)
+{
+  char e = 0;
+  d %= (unsigned) d;
+  e -= 0;
+  __builtin_strncpy (&a, &e, 1);
+  return e + b;
+}
+
+int
+main (void)
+{
+  c (~0);
+  return 0;
+}
diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index 3160ca3f88a..60087dd5e7b 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -1524,6 +1524,11 @@ remap_gimple_stmt (gimple *stmt, copy_body_data *id)
 	  : !opt_for_fn (id->dst_fn, flag_var_tracking_assignments)))
     return NULL;
 
+  if (!is_gimple_debug (stmt)
+      && id->param_body_adjs
+      && id->param_body_adjs->m_dead_stmts.contains (stmt))
+    return NULL;
+
   /* Begin by recognizing trees that we'll completely rewrite for the
      inlining context.  Our output for these trees is completely
      different from our input (e.g. RETURN_EXPR is deleted and morphs
@@ -1788,10 +1793,15 @@ remap_gimple_stmt (gimple *stmt, copy_body_data *id)
 
       if (gimple_debug_bind_p (stmt))
 	{
+	  tree value;
+	  if (id->param_body_adjs
+	      && id->param_body_adjs->m_dead_stmts.contains (stmt))
+	    value = NULL_TREE;
+	  else
+	    value = gimple_debug_bind_get_value (stmt);
 	  gdebug *copy
 	    = gimple_build_debug_bind (gimple_debug_bind_get_var (stmt),
-				       gimple_debug_bind_get_value (stmt),
-				       stmt);
+				       value, stmt);
 	  if (id->reset_location)
 	    gimple_set_location (copy, input_location);
 	  id->debug_stmts.safe_push (copy);
@@ -2671,7 +2681,9 @@ copy_phis_for_bb (basic_block bb, copy_body_data *id)
       phi = si.phi ();
       res = PHI_RESULT (phi);
       new_res = res;
-      if (!virtual_operand_p (res))
+      if (!virtual_operand_p (res)
+	  && (!id->param_body_adjs
+	      || !id->param_body_adjs->m_dead_stmts.contains (phi)))
 	{
 	  walk_tree (&new_res, copy_tree_body_r, id, NULL);
 	  if (EDGE_COUNT (new_bb->preds) == 0)
-- 
2.26.2



More information about the Gcc-patches mailing list