Handle sibcalls with aggregate returns

We treated this g as a sibling call to f:

      int f (int);
      int g (void) { return f (1); }

but not this one:

      struct s { int i; };
      struct s f (int);
      struct s g (void) { return f (1); }

We treated them both as sibcalls on x86 before the first patch for PR36326,
so I suppose this is a regression of sorts from 4.3.

The patch allows function returns to be local aggregate variables as well
as gimple registers.

gcc/
	* tree-tailcall.c (process_assignment): Simplify the check for
	a valid copy, allowing the source to be a local variable as
	well as an SSA name.
	(find_tail_calls): Allow copies between local variables to follow
	the call.  Allow the result to be stored in any local variable,
	even if it's an aggregate.
	(eliminate_tail_call): Check whether the result is an SSA name
	before updating its SSA_NAME_DEF_STMT.

gcc/testsuite/
	* gcc.dg/tree-ssa/tailcall-7.c: New test.

From-SVN: r242668

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 171107e8345131837702e0c13249fb45dc7a2dae..56fa35b269152833505f3e6be50ba9d4a847fa87 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,14 @@
+2016-11-21  Richard Sandiford  <richard.sandiford@arm.com>
+
+       * tree-tailcall.c (process_assignment): Simplify the check for
+       a valid copy, allowing the source to be a local variable as
+       well as an SSA name.
+       (find_tail_calls): Allow copies between local variables to follow
+       the call.  Allow the result to be stored in any local variable,
+       even if it's an aggregate.
+       (eliminate_tail_call): Check whether the result is an SSA name
+       before updating its SSA_NAME_DEF_STMT.
+
 2016-11-21  David Malcolm  <dmalcolm@redhat.com>
 
        PR preprocessor/78324

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 16196967f43dace5913bd3380b25a90d3ed4d5e4..828c941265ea9c40ebcbf3f25d24b04c58545064 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2016-11-21  Richard Sandiford  <richard.sandiford@arm.com>
+
+       * gcc.dg/tree-ssa/tailcall-7.c: New test.
+
 2016-11-21  David Malcolm  <dmalcolm@redhat.com>
 
        PR preprocessor/78324

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/tailcall-7.c b/gcc/testsuite/gcc.dg/tree-ssa/tailcall-7.c
new file mode 100644 (file)
index 0000000..eabf1a8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/tailcall-7.c
@@ -0,0 +1,89 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-tailc-details" } */
+
+struct s { int x; };
+struct s f (int);
+struct s global;
+void callit (void (*) (void));
+
+/* Tail call.  */
+void
+g1 (void)
+{
+  f (1);
+}
+
+/* Not a tail call.  */
+void
+g2 (void)
+{
+  global = f (2);
+}
+
+/* Not a tail call.  */
+void
+g3 (struct s *ptr)
+{
+  *ptr = f (3);
+}
+
+/* Tail call.  */
+struct s
+g4 (struct s param)
+{
+  param = f (4);
+  return param;
+}
+
+/* Tail call.  */
+struct s
+g5 (void)
+{
+  struct s local = f (5);
+  return local;
+}
+
+/* Tail call.  */
+struct s
+g6 (void)
+{
+  return f (6);
+}
+
+/* Not a tail call.  */
+struct s
+g7 (void)
+{
+  struct s local = f (7);
+  global = local;
+  return local;
+}
+
+/* Not a tail call.  */
+struct s
+g8 (struct s *ptr)
+{
+  struct s local = f (8);
+  *ptr = local;
+  return local;
+}
+
+/* Not a tail call.  */
+int
+g9 (struct s param)
+{
+  void inner (void) { param = f (9); }
+  callit (inner);
+  return 9;
+}
+
+/* Tail call.  */
+int
+g10 (int param)
+{
+  void inner (void) { f (param); }
+  callit (inner);
+  return 10;
+}
+
+/* { dg-final { scan-tree-dump-times "Found tail call" 5 "tailc" } } */

diff --git a/gcc/tree-tailcall.c b/gcc/tree-tailcall.c
index 0436f0f04a643550dfa8facd61e45aa6f795e337..f97541d35a544ab83ebe0de5aa13fe419e614e71 100644 (file)
--- a/gcc/tree-tailcall.c
+++ b/gcc/tree-tailcall.c
@@ -269,7 +269,7 @@ process_assignment (gassign *stmt, gimple_stmt_iterator call, tree *m,
      conversions that can never produce extra code between the function
      call and the function return.  */
   if ((rhs_class == GIMPLE_SINGLE_RHS || gimple_assign_cast_p (stmt))
-      && (TREE_CODE (src_var) == SSA_NAME))
+      && src_var == *ass_var)
     {
       /* Reject a tailcall if the type conversion might need
         additional code.  */
@@ -287,9 +287,6 @@ process_assignment (gassign *stmt, gimple_stmt_iterator call, tree *m,
            return false;
        }
 
-      if (src_var != *ass_var)
-       return false;
-
       *ass_var = dest;
       return true;
     }
@@ -428,6 +425,13 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
          break;
        }
 
+      /* Allow simple copies between local variables, even if they're
+        aggregates.  */
+      if (is_gimple_assign (stmt)
+         && auto_var_in_fn_p (gimple_assign_lhs (stmt), cfun->decl)
+         && auto_var_in_fn_p (gimple_assign_rhs1 (stmt), cfun->decl))
+       continue;
+
       /* If the statement references memory or volatile operands, fail.  */
       if (gimple_references_memory_p (stmt)
          || gimple_has_volatile_ops (stmt))
@@ -444,18 +448,20 @@ find_tail_calls (basic_block bb, struct tailcall **ret)
       return;
     }
 
-  /* If the LHS of our call is not just a simple register, we can't
-     transform this into a tail or sibling call.  This situation happens,
-     in (e.g.) "*p = foo()" where foo returns a struct.  In this case
-     we won't have a temporary here, but we need to carry out the side
-     effect anyway, so tailcall is impossible.
+  /* If the LHS of our call is not just a simple register or local
+     variable, we can't transform this into a tail or sibling call.
+     This situation happens, in (e.g.) "*p = foo()" where foo returns a
+     struct.  In this case we won't have a temporary here, but we need
+     to carry out the side effect anyway, so tailcall is impossible.
 
      ??? In some situations (when the struct is returned in memory via
      invisible argument) we could deal with this, e.g. by passing 'p'
      itself as that argument to foo, but it's too early to do this here,
      and expand_call() will not handle it anyway.  If it ever can, then
      we need to revisit this here, to allow that situation.  */
-  if (ass_var && !is_gimple_reg (ass_var))
+  if (ass_var
+      && !is_gimple_reg (ass_var)
+      && !auto_var_in_fn_p (ass_var, cfun->decl))
     return;
 
   /* We found the call, check whether it is suitable.  */
@@ -888,7 +894,7 @@ eliminate_tail_call (struct tailcall *t)
 
   call = gsi_stmt (t->call_gsi);
   rslt = gimple_call_lhs (call);
-  if (rslt != NULL_TREE)
+  if (rslt != NULL_TREE && TREE_CODE (rslt) == SSA_NAME)
     {
       /* Result of the call will no longer be defined.  So adjust the
         SSA_NAME_DEF_STMT accordingly.  */