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Fix looping flag discovery in ipa-pure-const 

The testcase shows situation where there is non-trivial cycle in the callgraph
involving a noreturn call.  This cycle is important for const function discovery
but not important for pure.  IPA pure const uses same strongly connected
components for both propagations which makes it to get suboptimal result
(does not detect the pure flag). However local pure const gets the situation
right becaue it processes functions in right order.  This hits rarely
executed code in propagate_pure_const that merge results with previously
known state that has long standing bug in it that makes it to throw away
the looping flag.

Bootstrapped/regtested x86_64-linux.

gcc/ChangeLog:

2021-11-21  Jan Hubicka  <hubicka@ucw.cz>

	PR ipa/103052
	* ipa-pure-const.c (propagate_pure_const): Fix merging of loping flag.

gcc/testsuite/ChangeLog:

2021-11-21  Jan Hubicka  <hubicka@ucw.cz>

	PR ipa/103052
	* gcc.c-torture/execute/pr103052.c: New test.
This commit is contained in:
Jan Hubicka 2021-11-21 00:35:22 +01:00
parent 7950c96ca6
commit a0e99d5bb7
2 changed files with 37 additions and 2 deletions
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4
gcc/ipa-pure-const.c
View File

@ -1782,9 +1782,9 @@ propagate_pure_const (void)
if (w_l->state_previously_known != IPA_NEITHER
&& this_state > w_l->state_previously_known)
{
this_state = w_l->state_previously_known;
if (this_state == IPA_NEITHER)
this_looping = w_l->looping_previously_known;
this_looping = w_l->looping_previously_known;
this_state = w_l->state_previously_known;
}
if (!this_looping && self_recursive_p (w))
this_looping = true;

35
gcc/testsuite/gcc.c-torture/execute/pr103052.c Normal file
View File

@ -0,0 +1,35 @@
static void js_error(void);
static int top;
static void js_throw(void)
{
__builtin_exit(0);
}
// LOCATION A -- if js_pop is here, the bug is present
static void js_pop(void)
{
if (++top > 100)
js_error();
}
static void jsC_error(const char *v)
{
if (v[0] == 0)
js_error();
js_throw();
}
static void checkfutureword(const char *exp)
{
if (!__builtin_strcmp(exp, "const"))
jsC_error("boom");
}
static void js_error(void) {
checkfutureword("foo");
checkfutureword("bar");
js_pop();
}
int main(void)
{
checkfutureword("const");
__builtin_abort ();
}