When musttail is set, make tree-tailcall to give error messages
when it cannot handle a call. This avoids vague "other reasons"
error messages later at expand time.
This doesn't always work, for example when find_tail_call
walking gives up because the control flow is too complicated
then it won't find the tail call and can't give a suitable
error message.
gcc/ChangeLog:
* tree-tailcall.cc (maybe_error_musttail): Add.
(find_tail_calls): Add error messages.
---
gcc/tree-tailcall.cc | 37 ++++++++++++++++++++++++++++++++++---
1 file changed, 34 insertions(+), 3 deletions(-)
diff --git a/gcc/tree-tailcall.cc b/gcc/tree-tailcall.cc
index 094856de22ef..1217435c3f90 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 +403,20 @@ 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);
+ }
+}
+
/* 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;
@@ -489,8 +504,14 @@ 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;
+ }
+ /* This doesn't really work because the BB would have multiple succ edges
+ and is rejected above. Instead just gives a "other reasons" error
+ at expand time. */
/* 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)
@@ -524,7 +545,10 @@ 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 +629,7 @@ 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 +638,7 @@ 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;
}
}
@@ -631,6 +657,8 @@ find_tail_calls (basic_block bb, struct tailcall **ret,
bool only_musttail)
auto_bitmap to_move_defs;
auto_vec<gimple *> to_move_stmts;
+ /* Does not give musttail errors because the frontend won't generate
+ such musttails. */
abb = bb;
agsi = gsi;
while (1)
@@ -716,7 +744,10 @@ 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. */
--
2.44.0
