Hi!
The following patch makes some adjustments so that users can analyze what
calls weren't tail called even without using musttail attribute (though I'm
still not convinced it should be a warning, because we don't distinguish
between calls in return call (...); statements vs. calls that just happened
to end up in tail positions because something has been optimized away etc.
E.g. for
int foo (int, int, int, int, int, int, int);
int bar (int);
void qux (int *);
int
baz (int x)
{
if (x)
return foo (1, 2, 3, 4, 5, 6, 7);
else
{
int y;
qux (&y);
return bar (x);
}
}
./xgcc -B ./ -S -O2 -fdump-{tree-tailc,rtl-expand}-details pr119718.c ; grep
-B1 '^\(;; \)\?Cannot tail-call:' pr119718.c.*
pr119718.c.222t.tailc-_7 = bar (0);
pr119718.c.222t.tailc:Cannot tail-call: call invocation refers to locals
--
pr119718.c.270r.expand-;; foo (1, 2, 3, 4, 5, 6, 7) [tail call]
pr119718.c.270r.expand:;; Cannot tail-call: callee required more stack slots
than the caller
The changes are:
1) in tailc pass use wording more consistent with the musttail error wording
2) do it only in *-details dump
3) add similar diagnostics on the expand side, but this time only for the
CALL_EXPR_TAILCALL calls, if something wasn't marked that way, it is up
to tailc pass to emit message about it, if it was and it still can't be
tail called, let it tell users about that; in this case I need
to use the ;; prefix because it will appear in the middle of
the IL dump and ;; is what is used for such purposes in other spots
4) I've tried to improve formatting of the maybe_error_musttail and
maybe_complain_about_tail_call calls
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2025-04-11 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/119718
* tree-tailcall.cc (maybe_error_musttail): Only dump into dump_file
if dump_flags & TDF_DETAILS. Use "Cannot tail-call: " prefix instead
of "Cannot convert: ".
(find_tail_calls, tree_optimize_tail_calls_1): Formatting fixes
for maybe_error_musttail calls.
* calls.cc (maybe_complain_about_tail_call): Emit also a message
into dump_file when dump_flags & TDF_DETAILS for CALL_EXPR_TAILCALL
calls.
(initialize_argument_information): Formatting fix for
maybe_complain_about_tail_call calls.
(can_implement_as_sibling_call_p, expand_call): Likewise.
--- gcc/tree-tailcall.cc.jj 2025-04-08 14:09:32.189711950 +0200
+++ gcc/tree-tailcall.cc 2025-04-11 09:38:22.483257379 +0200
@@ -492,10 +492,10 @@ maybe_error_musttail (gcall *call, const
gimple_call_set_must_tail (call, false); /* Avoid another error. */
gimple_call_set_tail (call, false);
}
- if (dump_file)
+ if (dump_file && (dump_flags & TDF_DETAILS))
{
print_gimple_stmt (dump_file, call, 0, TDF_SLIM);
- fprintf (dump_file, "Cannot convert: %s\n", err);
+ fprintf (dump_file, "Cannot tail-call: %s\n", err);
}
}
@@ -596,9 +596,8 @@ find_tail_calls (basic_block bb, struct
return;
if (bad_stmt)
{
- maybe_error_musttail (call,
- _("memory reference or volatile after "
- "call"), diag_musttail);
+ maybe_error_musttail (call, _("memory reference or volatile "
+ "after call"), diag_musttail);
return;
}
ass_var = gimple_call_lhs (call);
@@ -711,9 +710,8 @@ find_tail_calls (basic_block bb, struct
if (!e)
{
- maybe_error_musttail (call,
- _("call may throw exception that does not "
- "propagate"), diag_musttail);
+ maybe_error_musttail (call, _("call may throw exception that does not "
+ "propagate"), diag_musttail);
return;
}
@@ -721,9 +719,9 @@ find_tail_calls (basic_block bb, struct
|| !empty_eh_cleanup (e->dest, 20)
|| EDGE_COUNT (bb->succs) > 2)
{
- maybe_error_musttail (call,
- _("call may throw exception caught locally "
- "or perform cleanups"), diag_musttail);
+ maybe_error_musttail (call, _("call may throw exception caught "
+ "locally or perform cleanups"),
+ diag_musttail);
return;
}
}
@@ -854,9 +852,8 @@ find_tail_calls (basic_block bb, struct
}
if (local_live_vars)
BITMAP_FREE (local_live_vars);
- maybe_error_musttail (call,
- _("call invocation refers to locals"),
- diag_musttail);
+ maybe_error_musttail (call, _("call invocation refers to "
+ "locals"), diag_musttail);
return;
}
else
@@ -883,9 +880,8 @@ find_tail_calls (basic_block bb, struct
continue;
}
BITMAP_FREE (local_live_vars);
- maybe_error_musttail (call,
- _("call invocation refers to locals"),
- diag_musttail);
+ maybe_error_musttail (call, _("call invocation refers to "
+ "locals"), diag_musttail);
return;
}
}
@@ -1020,8 +1016,7 @@ find_tail_calls (basic_block bb, struct
if (!VOID_TYPE_P (rettype)
&& !useless_type_conversion_p (rettype, calltype))
{
- maybe_error_musttail (call,
- _("call and return value are different"),
+ maybe_error_musttail (call, _("call and return value are different"),
diag_musttail);
return;
}
@@ -1092,8 +1087,7 @@ find_tail_calls (basic_block bb, struct
}
if (!ok)
{
- maybe_error_musttail (call,
- _("call and return value are different"),
+ maybe_error_musttail (call, _("call and return value are different"),
diag_musttail);
return;
}
@@ -1103,18 +1097,16 @@ find_tail_calls (basic_block bb, struct
multiplicands. */
if (!tail_recursion && (m || a))
{
- maybe_error_musttail (call,
- _("operations after non tail recursive call"),
- diag_musttail);
+ maybe_error_musttail (call, _("operations after non tail recursive "
+ "call"), diag_musttail);
return;
}
/* For pointers only allow additions. */
if (m && POINTER_TYPE_P (TREE_TYPE (DECL_RESULT (current_function_decl))))
{
- maybe_error_musttail (call,
- _("tail recursion with pointers can only use "
- "additions"), diag_musttail);
+ maybe_error_musttail (call, _("tail recursion with pointers can only "
+ "use additions"), diag_musttail);
return;
}
@@ -1594,10 +1586,10 @@ tree_optimize_tail_calls_1 (bool opt_tai
struct tailcall *a = *p;
*p = (*p)->next;
gcall *call = as_a <gcall *> (gsi_stmt (a->call_gsi));
- maybe_error_musttail (call,
- _("tail recursion with accumulation "
- "mixed with musttail "
- "non-recursive call"), diag_musttail);
+ maybe_error_musttail (call, _("tail recursion with "
+ "accumulation mixed with "
+ "musttail non-recursive call"),
+ diag_musttail);
free (a);
}
else
--- gcc/calls.cc.jj 2025-04-08 14:08:48.472320552 +0200
+++ gcc/calls.cc 2025-04-11 10:02:22.211243184 +0200
@@ -1273,11 +1273,19 @@ void
maybe_complain_about_tail_call (tree call_expr, const char *reason)
{
gcc_assert (TREE_CODE (call_expr) == CALL_EXPR);
- if (!CALL_EXPR_MUST_TAIL_CALL (call_expr))
- return;
-
- error_at (EXPR_LOCATION (call_expr), "cannot tail-call: %s", reason);
- CALL_EXPR_MUST_TAIL_CALL (call_expr) = 0;
+ if (CALL_EXPR_MUST_TAIL_CALL (call_expr))
+ {
+ error_at (EXPR_LOCATION (call_expr), "cannot tail-call: %s", reason);
+ CALL_EXPR_MUST_TAIL_CALL (call_expr) = 0;
+ }
+ if (CALL_EXPR_TAILCALL (call_expr)
+ && dump_file
+ && (dump_flags & TDF_DETAILS))
+ {
+ fprintf (dump_file, ";; ");
+ print_generic_expr (dump_file, call_expr, TDF_SLIM);
+ fprintf (dump_file, "\n;; Cannot tail-call: %s\n", reason);
+ }
}
/* Fill in ARGS_SIZE and ARGS array based on the parameters found in
@@ -1447,10 +1455,10 @@ initialize_argument_information (int num
if (!call_from_thunk_p && DECL_P (base) && !TREE_STATIC (base))
{
*may_tailcall = false;
- maybe_complain_about_tail_call (exp,
- _("a callee-copied argument
is"
- " stored in the current"
- " function's frame"));
+ maybe_complain_about_tail_call (exp, _("a callee-copied "
+ "argument is stored "
+ "in the current "
+ "function's frame"));
}
args[i].tree_value = build_fold_addr_expr_loc (loc,
@@ -2534,10 +2542,9 @@ can_implement_as_sibling_call_p (tree ex
if (!targetm.have_sibcall_epilogue ()
&& !targetm.emit_epilogue_for_sibcall)
{
- maybe_complain_about_tail_call
- (exp,
- _("machine description does not have"
- " a sibcall_epilogue instruction pattern"));
+ maybe_complain_about_tail_call (exp, _("machine description does not "
+ "have a sibcall_epilogue "
+ "instruction pattern"));
return false;
}
@@ -2555,9 +2562,8 @@ can_implement_as_sibling_call_p (tree ex
into a sibcall. */
if (!targetm.function_ok_for_sibcall (fndecl, exp))
{
- maybe_complain_about_tail_call (exp,
- _("target is not able to optimize the"
- " call into a sibling call"));
+ maybe_complain_about_tail_call (exp, _("target is not able to optimize "
+ "the call into a sibling call"));
return false;
}
@@ -2606,9 +2612,8 @@ can_implement_as_sibling_call_p (tree ex
if (maybe_gt (args_size.constant,
crtl->args.size - crtl->args.pretend_args_size))
{
- maybe_complain_about_tail_call (exp,
- _("callee required more stack slots"
- " than the caller"));
+ maybe_complain_about_tail_call (exp, _("callee required more stack "
+ "slots than the caller"));
return false;
}
@@ -2621,9 +2626,8 @@ can_implement_as_sibling_call_p (tree ex
(current_function_decl),
crtl->args.size)))
{
- maybe_complain_about_tail_call (exp,
- _("inconsistent number of"
- " popped arguments"));
+ maybe_complain_about_tail_call (exp, _("inconsistent number of"
+ " popped arguments"));
return false;
}
@@ -2685,7 +2689,7 @@ expand_call (tree exp, rtx target, int i
so this shouldn't really happen unless the
the musttail pass gave up walking before finding the call. */
if (!try_tail_call)
- maybe_complain_about_tail_call (exp, _("other reasons"));
+ maybe_complain_about_tail_call (exp, _("other reasons"));
int pass;
/* Register in which non-BLKmode value will be returned,
@@ -3092,8 +3096,9 @@ expand_call (tree exp, rtx target, int i
if (MEM_P (*iter))
{
try_tail_call = 0;
- maybe_complain_about_tail_call (exp,
- _("hidden string length argument passed on
stack"));
+ maybe_complain_about_tail_call (exp, _("hidden string length "
+ "argument passed on "
+ "stack"));
break;
}
}
@@ -3140,10 +3145,9 @@ expand_call (tree exp, rtx target, int i
|| partial_subreg_p (caller_mode, callee_mode)))))
{
try_tail_call = 0;
- maybe_complain_about_tail_call (exp,
- _("caller and callee disagree in"
- " promotion of function"
- " return value"));
+ maybe_complain_about_tail_call (exp, _("caller and callee disagree "
+ "in promotion of function "
+ "return value"));
}
}
Jakub
