[I slightly improve the patch covering a few more cases where
tree-tailcall gives up, especially with -O1 and -Os.
Here's the updated version.]
Give better error messages for musttail
When musttail is set, make tree-tailcall give error messages
when it cannot handle a call. This avoids vague "other reasons"
error messages later at expand time when it sees a musttail
function not marked tail call.
gcc/ChangeLog:
* tree-tailcall.cc (maybe_error_musttail): Add.
(bb_get_succ_edge_count): Add.
(find_tail_calls): Add error messages. Keep searching
for basic blocks with multiple BBs if all but one is EH
only.
diff --git a/gcc/tree-tailcall.cc b/gcc/tree-tailcall.cc
index 094856de22ef..7268e8138529 100644
--- a/gcc/tree-tailcall.cc
+++ b/gcc/tree-tailcall.cc
@@ -43,6 +43,7 @@ along with GCC; see the file COPYING3. If not see
#include "common/common-target.h"
#include "ipa-utils.h"
#include "tree-ssa-live.h"
+#include "diagnostic-core.h"
/* The file implements the tail recursion elimination. It is also used to
analyze the tail calls in general, passing the results to the rtl level
@@ -402,6 +403,36 @@ propagate_through_phis (tree var, edge e)
return var;
}
+/* Report an error for failing to tail convert must call CALL
+ with error message ERR. */
+
+static void
+maybe_error_musttail (gcall *call, const char *err)
+{
+ if (gimple_call_must_tail_p (call))
+ {
+ error_at (call->location, "cannot tail-call: %s", err);
+ gimple_call_set_must_tail (call, false); /* Avoid another error. */
+ gimple_call_set_tail (call, false);
+ }
+}
+
+/* Count succ edges for BB and return in NUM_OTHER and NUM_EH. */
+
+static void
+bb_get_succ_edge_count (basic_block bb, int &num_other, int &num_eh)
+{
+ edge e;
+ edge_iterator ei;
+ num_eh = 0;
+ num_other = 0;
+ FOR_EACH_EDGE (e, ei, bb->succs)
+ if (e->flags & EDGE_EH)
+ num_eh++;
+ else
+ num_other++;
+}
+
/* Argument for compute_live_vars/live_vars_at_stmt and what compute_live_vars
returns. Computed lazily, but just once for the function. */
static live_vars_map *live_vars;
@@ -426,8 +457,16 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
tree var;
if (!single_succ_p (bb))
- return;
+ {
+ int num_eh, num_other;
+ bb_get_succ_edge_count (bb, num_eh, num_other);
+ /* Allow a single EH edge so that we can give a better
+ error message later. */
+ if (!(num_eh == 1 && num_other == 1))
+ return;
+ }
+ bool bad_stmt = false;
for (gsi = gsi_last_bb (bb); !gsi_end_p (gsi); gsi_prev (&gsi))
{
stmt = gsi_stmt (gsi);
@@ -448,6 +487,11 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
/* Handle only musttail calls when not optimizing. */
if (only_musttail && !gimple_call_must_tail_p (call))
return;
+ if (bad_stmt)
+ {
+ maybe_error_musttail (call, "Memory reference or volatile after
call");
+ return;
+ }
ass_var = gimple_call_lhs (call);
break;
}
@@ -462,7 +506,9 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
/* If the statement references memory or volatile operands, fail. */
if (gimple_references_memory_p (stmt)
|| gimple_has_volatile_ops (stmt))
- return;
+ {
+ bad_stmt = true;
+ }
}
if (gsi_end_p (gsi))
@@ -489,13 +535,21 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
if (ass_var
&& !is_gimple_reg (ass_var)
&& !auto_var_in_fn_p (ass_var, cfun->decl))
- return;
+ {
+ maybe_error_musttail (call, "complex return value");
+ return;
+ }
/* If the call might throw an exception that wouldn't propagate out of
cfun, we can't transform to a tail or sibling call (82081). */
- if (stmt_could_throw_p (cfun, stmt)
+ if ((stmt_could_throw_p (cfun, stmt)
&& !stmt_can_throw_external (cfun, stmt))
+ || !single_succ_p (bb))
+ {
+ maybe_error_musttail (call,
+ "call may throw exception that does not propagate");
return;
+ }
/* If the function returns a value, then at present, the tail call
must return the same type of value. There is conceptually a copy
@@ -524,7 +578,10 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
if (result_decl
&& may_be_aliased (result_decl)
&& ref_maybe_used_by_stmt_p (call, result_decl, false))
- return;
+ {
+ maybe_error_musttail (call, "tail call must be same type");
+ return;
+ }
/* We found the call, check whether it is suitable. */
tail_recursion = false;
@@ -605,6 +662,7 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
{
if (local_live_vars)
BITMAP_FREE (local_live_vars);
+ maybe_error_musttail (call, "call invocation refers to locals");
return;
}
else
@@ -613,6 +671,7 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
if (bitmap_bit_p (local_live_vars, *v))
{
BITMAP_FREE (local_live_vars);
+ maybe_error_musttail (call, "call invocation refers to
locals");
return;
}
}
@@ -658,17 +717,21 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
continue;
if (gimple_code (stmt) != GIMPLE_ASSIGN)
- return;
+ {
+ maybe_error_musttail (call, "unhandled code after call");
+ return;
+ }
/* This is a gimple assign. */
par ret = process_assignment (as_a <gassign *> (stmt), gsi,
&tmp_m, &tmp_a, &ass_var, to_move_defs);
- if (ret == FAIL)
- return;
+ if (ret == FAIL || (ret == TRY_MOVE && !tail_recursion))
+ {
+ maybe_error_musttail (call, "return value changed after call");
+ return;
+ }
else if (ret == TRY_MOVE)
{
- if (! tail_recursion)
- return;
/* Do not deal with checking dominance, the real fix is to
do path isolation for the transform phase anyway, removing
the need to compute the accumulators with new stmts. */
@@ -716,16 +779,25 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
if (ret_var
&& (ret_var != ass_var
&& !(is_empty_type (TREE_TYPE (ret_var)) && !ass_var)))
- return;
+ {
+ maybe_error_musttail (call, "call must be the same type");
+ return;
+ }
/* If this is not a tail recursive call, we cannot handle addends or
multiplicands. */
if (!tail_recursion && (m || a))
- return;
+ {
+ maybe_error_musttail (call, "operations after non tail recursive call");
+ return;
+ }
/* For pointers only allow additions. */
if (m && POINTER_TYPE_P (TREE_TYPE (DECL_RESULT (current_function_decl))))
- return;
+ {
+ maybe_error_musttail (call, "tail recursion with pointers can only use
additions");
+ return;
+ }
/* Move queued defs. */
if (tail_recursion)
