https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108988
Bug ID: 108988
Summary: gimple_fold_builtin_fputs doesn't preserve
gimple_builtin_call_types_compatible_p
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: dmalcolm at gcc dot gnu.org
Target Milestone: ---
Whilst working on PR analyzer/107565, I noticed that in this function:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
typedef struct FILE FILE;
FILE* fopen (const char*, const char*);
int fprintf (FILE *, const char *, ...);
#define NULL ((void *)0)
void
test_2 (void)
{
int i;
for (i = 0; i < 2; ++i) {
FILE *fp = fopen ("/tmp/test", "w");
fprintf (fp, "hello");
}
} // should report a leak here
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
the fprintf (fp, "hello"); is optimized to:
__builtin_fwrite ("hello", 1, 5, fp);
but this call has:
(gdb) p gimple_builtin_call_types_compatible_p (repl, gimple_call_fndecl
(repl))
$23 = false
Specifically, the fprintf is optimized to:
__builtin_fputs ("hello", fp);
Within gimple_fold_builtin_fprintf this has:
(gdb) call debug(stmt)
__builtin_fputs ("hello", fp);
(gdb) p gimple_builtin_call_types_compatible_p (stmt, gimple_call_fndecl
(stmt))
$19 = true
which is optimized to:
(gdb) call debug(repl)
__builtin_fwrite ("hello", 1, 5, fp);
(gdb) p gimple_builtin_call_types_compatible_p (repl, gimple_call_fndecl
(repl))
$23 = false
Note how the resulting call has "false" for
gimple_builtin_call_types_compatible_p; this is due to argument idx 2 (the 5):
(gdb) p i
$13 = 2
(gdb) p arg
$14 = <integer_cst 0x7fffea7f9ba0>
(gdb) call debug_tree(arg)
<integer_cst 0x7fffea7f9ba0 type <integer_type 0x7fffea663150 ssizetype>
constant 5>
In the analyzer I'm checking that gimple_builtin_call_types_compatible_p is
true when handling a builtin that it "knows" how to handle, otherwise the
analyzer falls back to assuming that the call could have arbitrary side-effects
(e.g. fclose-ing the file, hence it stops reporting the leak).
Is this a bug in gimple_fold_builtin_fprintf?
