ipa-utils: avoid uninitialized probabilities on ICF [PR111559]

r14-3459-g0c78240fd7d519 "Check that passes do not forget to define profile"
exposed check failures in cases when gcc produces uninitialized profile
probabilities. In case of PR/111559 uninitialized profile is generated
by edges executed 0 times reported by IPA profile:

    $ gcc -O2 -fprofile-generate pr111559.c -o b -fopt-info
    $ ./b
    $ gcc -O2 -fprofile-use -fprofile-correction pr111559.c -o b -fopt-info

    pr111559.c: In function 'rule1':
    pr111559.c:6:13: error: probability of edge 3->4 not initialized
        6 | static void rule1(void) { if (p) edge(); }
          |             ^~~~~
    during GIMPLE pass: fixup_cfg
    pr111559.c:6:13: internal compiler error: verify_flow_info failed

The change conservatively ignores updates with zero execution counts and
uses initially assigned probabilities (`always` probability in case of
the example).

	PR ipa/111283
	PR gcov-profile/111559

gcc/
	* ipa-utils.cc (ipa_merge_profiles): Avoid producing
	uninitialized probabilities when merging counters with zero
	denominators.

gcc/testsuite/
	* gcc.dg/tree-prof/pr111559.c: New test.

0 files changed, 0 insertions, 0 deletions