[Bug tree-optimization/79529] New: [7 Regression] ICE in is_maybe_undefined (tree-ssa-loop-unswitch.c:162)

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79529

            Bug ID: 79529
           Summary: [7 Regression] ICE in is_maybe_undefined
                    (tree-ssa-loop-unswitch.c:162)
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: aldyh at gcc dot gnu.org, jamborm at gcc dot gnu.org
  Target Milestone: ---

Building Firefox with -flto and -O3, one can get:

/home/marxin/Programming/gecko-dev/intl/icu/source/i18n/dtptngen.cpp:1379:1:
internal compiler error: Segmentation fault
 DateTimePatternGenerator::getBestAppending(int32_t missingFields, int32_t
flags, UDateTimePatternMatchOptions options) {
 ^
0xcaea52 crash_signal
        ../../gcc/toplev.c:333
0x888c28 dominated_by_p(cdi_direction, basic_block_def const*, basic_block_def
const*)
        ../../gcc/dominance.c:1117
0xe465f0 is_maybe_undefined
        ../../gcc/tree-ssa-loop-unswitch.c:162
0xe46863 tree_may_unswitch_on
        ../../gcc/tree-ssa-loop-unswitch.c:222
0xe46beb tree_unswitch_single_loop
        ../../gcc/tree-ssa-loop-unswitch.c:322
0xe46379 tree_ssa_unswitch_loops()
        ../../gcc/tree-ssa-loop-unswitch.c:102
0xe48337 execute
        ../../gcc/tree-ssa-loop-unswitch.c:935

Problem is that:

if (dominated_by_p (CDI_DOMINATORS, loop->header, gimple_bb (def)))

where def is a gimple nop, which has gimple_bb (def) == NULL.

I guess following patch should fix that:

diff --git a/gcc/tree-ssa-loop-unswitch.c b/gcc/tree-ssa-loop-unswitch.c
index 4ef3a6bf80a..5716c99e58c 100644
--- a/gcc/tree-ssa-loop-unswitch.c
+++ b/gcc/tree-ssa-loop-unswitch.c
@@ -141,6 +141,9 @@ is_maybe_undefined (const tree name, gimple *stmt, struct
loop *loop)

       gimple *def = SSA_NAME_DEF_STMT (t);

+      if (gimple_nop_p (def))
+       return true;
+
       /* Check that all the PHI args are fully defined.  */
       if (gphi *phi = dyn_cast <gphi *> (def))
        {