[Bug tree-optimization/78601] New: [7 regression] test case gcc.dg/uninit-pred-6_a.c and gcc.dg/uninit-pred-7_c.c fail starting with r242639

[seurer at linux dot vnet.ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78601

            Bug ID: 78601
           Summary: [7 regression] test case gcc.dg/uninit-pred-6_a.c and
                    gcc.dg/uninit-pred-7_c.c fail starting with r242639
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: seurer at linux dot vnet.ibm.com
  Target Milestone: ---

Running /home/seurer/gcc/gcc-test2/gcc/testsuite/gcc.dg/dg.exp ...
FAIL: gcc.dg/uninit-pred-6_a.c warning (test for warnings, line 36)

                === gcc Summary ===

# of expected passes            2
# of unexpected failures        1

It used to generate a warning but no longer does:

seurer@genoa:~/gcc/build/gcc-test2$ /home/seurer/gcc/build/gcc-test2/gcc/xgcc
-B/home/seurer/gcc/build/gcc-test2/gcc/
/home/seurer/gcc/gcc-test2/gcc/testsuite/gcc.dg/uninit-pred-6_a.c 
-fno-diagnostics-show-caret -fdiagnostics-color=never   -Wuninitialized -O2 -S 
 -o uninit-pred-6_a.s
/home/seurer/gcc/gcc-test2/gcc/testsuite/gcc.dg/uninit-pred-6_a.c: In function
'foo_2':
/home/seurer/gcc/gcc-test2/gcc/testsuite/gcc.dg/uninit-pred-6_a.c:36:7:
warning: 'v' may be used uninitialized in this function [-Wmaybe-uninitialized]


Running /home/seurer/gcc/gcc-test2/gcc/testsuite/gcc.dg/dg.exp ...
FAIL: gcc.dg/uninit-pred-7_c.c (internal compiler error)
FAIL: gcc.dg/uninit-pred-7_c.c warning (test for warnings, line 29)
FAIL: gcc.dg/uninit-pred-7_c.c (test for excess errors)

                === gcc Summary ===

# of unexpected failures        3

seurer@genoa:~/gcc/build/gcc-test2$ /home/seurer/gcc/build/gcc-test2/gcc/xgcc
-B/home/seurer/gcc/build/gcc-test2/gcc/
/home/seurer/gcc/gcc-test2/gcc/testsuite/gcc.dg/uninit-pred-7_c.c 
-fno-diagnostics-show-caret -fdiagnostics-color=never   -Wuninitialized -O2 -S 
 -o uninit-pred-7_c.s
/home/seurer/gcc/gcc-test2/gcc/testsuite/gcc.dg/uninit-pred-7_c.c: In function
'foo':
/home/seurer/gcc/gcc-test2/gcc/testsuite/gcc.dg/uninit-pred-7_c.c:9:5: internal
compiler error: in operator[], at vec.h:732
0x10b5afbb vec<pred_info, va_heap, vl_embed>::operator[](unsigned int)
        /home/seurer/gcc/gcc-test2/gcc/vec.h:732
0x10b5afbb vec<pred_info, va_heap, vl_ptr>::operator[](unsigned int)
        /home/seurer/gcc/gcc-test2/gcc/vec.h:1216
0x10b5afbb flatten_out_predicate_chains
        /home/seurer/gcc/gcc-test2/gcc/tree-ssa-uninit.c:2226
0x10b5afbb uninit_ops_invalidate_phi_use
        /home/seurer/gcc/gcc-test2/gcc/tree-ssa-uninit.c:2300
0x10b5b68f is_use_properly_guarded
        /home/seurer/gcc/gcc-test2/gcc/tree-ssa-uninit.c:2364
0x10b5cd8f find_uninit_use
        /home/seurer/gcc/gcc-test2/gcc/tree-ssa-uninit.c:2434
0x10b5cd8f warn_uninitialized_phi
        /home/seurer/gcc/gcc-test2/gcc/tree-ssa-uninit.c:2504
0x10b5cd8f execute
        /home/seurer/gcc/gcc-test2/gcc/tree-ssa-uninit.c:2612