Hi!
The following patch, when optimizing, replaces GIMPLE_RETURN in
noreturn functions right after warning about them with __builtin_unreachable
(). The advantage of that is that we don't emit unnecessary epilogues for
them and perhaps optimize away some other useless computations if the only
side-effect of those is feeding the return value.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2017-10-19 Jakub Jelinek <ja...@redhat.com>
PR target/82158
* tree-cfg.c (pass_warn_function_return::execute): In noreturn
functions when optimizing replace GIMPLE_RETURN stmts with
calls to __builtin_unreachable ().
* gcc.dg/tree-ssa/noreturn-1.c: New test.
--- gcc/tree-cfg.c.jj 2017-10-10 22:04:09.000000000 +0200
+++ gcc/tree-cfg.c 2017-10-19 18:41:04.843653944 +0200
@@ -9084,13 +9084,29 @@ pass_warn_function_return::execute (func
&& EDGE_COUNT (EXIT_BLOCK_PTR_FOR_FN (fun)->preds) > 0)
{
location = UNKNOWN_LOCATION;
- FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR_FOR_FN (fun)->preds)
+ for (ei = ei_start (EXIT_BLOCK_PTR_FOR_FN (fun)->preds);
+ (e = ei_safe_edge (ei)); )
{
last = last_stmt (e->src);
if ((gimple_code (last) == GIMPLE_RETURN
|| gimple_call_builtin_p (last, BUILT_IN_RETURN))
- && (location = gimple_location (last)) != UNKNOWN_LOCATION)
+ && location == UNKNOWN_LOCATION
+ && (location = gimple_location (last)) != UNKNOWN_LOCATION
+ && !optimize)
break;
+ /* When optimizing, replace return stmts in noreturn functions
+ with __builtin_unreachable () call. */
+ if (optimize && gimple_code (last) == GIMPLE_RETURN)
+ {
+ tree fndecl = builtin_decl_implicit (BUILT_IN_UNREACHABLE);
+ gimple *new_stmt = gimple_build_call (fndecl, 0);
+ gimple_set_location (new_stmt, gimple_location (last));
+ gimple_stmt_iterator gsi = gsi_for_stmt (last);
+ gsi_replace (&gsi, new_stmt, true);
+ remove_edge (e);
+ }
+ else
+ ei_next (&ei);
}
if (location == UNKNOWN_LOCATION)
location = cfun->function_end_locus;
--- gcc/testsuite/gcc.dg/tree-ssa/noreturn-1.c.jj 2017-10-19
18:50:53.861660409 +0200
+++ gcc/testsuite/gcc.dg/tree-ssa/noreturn-1.c 2017-10-19 18:55:32.270354804
+0200
@@ -0,0 +1,42 @@
+/* { dg-do compile } *
+/* { dg-options "-O2 -fdump-tree-ssa -std=gnu11" } */
+/* { dg-final { scan-tree-dump-times "__builtin_unreachable" 4 "ssa" } } */
+
+void bar1 (void);
+void bar2 (void);
+void bar3 (void);
+void bar4 (void);
+
+_Noreturn void
+foo1 (int *p, int y)
+{
+ bar1 ();
+ *p = y;
+ return; /* { dg-warning "function declared 'noreturn' has a 'return'
statement" } */
+} /* { dg-warning "'noreturn' function does return" "" { target
*-*-* } .-1 } */
+
+_Noreturn void
+foo2 (int *p, int y)
+{
+ bar2 ();
+ *p = y;
+} /* { dg-warning "'noreturn' function does return" } */
+
+_Noreturn void
+foo3 (int *p, int y)
+{
+ if (y > 10)
+ return; /* { dg-warning "function declared 'noreturn' has a 'return'
statement" } */
+ bar3 ();
+ *p = y;
+ return; /* { dg-warning "function declared 'noreturn' has a 'return'
statement" } */
+} /* { dg-warning "'noreturn' function does return" } */
+
+_Noreturn void
+foo4 (int *p, int y)
+{
+ if (y > 10)
+ return; /* { dg-warning "function declared 'noreturn' has a 'return'
statement" } */
+ bar4 ();
+ *p = y;
+} /* { dg-warning "'noreturn' function does return" } */
Jakub
