[Bug target/104112] New: ICE with -Ofast -march=armv8.2-a+sve -msve-vector-bits=512

[gilles.gouaillardet at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104112

            Bug ID: 104112
           Summary: ICE with -Ofast -march=armv8.2-a+sve
                    -msve-vector-bits=512
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gilles.gouaillardet at gmail dot com
  Target Milestone: ---

Created attachment 52226
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52226&action=edit
a simple reproducer

The attached reproducer (trimmed from BLAS) can be used to evidence a crash of
the compiler:

$ g++ -march=armv8.2-a+sve -msve-vector-bits=512 -Ofast -c boom.cpp 
during GIMPLE pass: vect
boom.cpp: In function ?void boom(int, double*, double*)?:
boom.cpp:4:1: internal compiler error: Segmentation fault
    4 | boom(int n,
      | ^~~~
0x10436f3 crash_signal
        ../.././gcc/toplev.c:328
0x12f86ec tree_class_check(tree_node*, tree_code_class, char const*, int, char
const*)
        ../.././gcc/tree.h:3495
0x12f86ec vect_create_partial_epilog
        ../.././gcc/tree-vect-loop.c:4953
0x13050ff vect_transform_cycle_phi(_loop_vec_info*, _stmt_vec_info*, gimple**,
_slp_tree*, _slp_instance*)
        ../.././gcc/tree-vect-loop.c:7728
0x12f562b vect_transform_stmt(vec_info*, _stmt_vec_info*,
gimple_stmt_iterator*, _slp_tree*, _slp_instance*)
        ../.././gcc/tree-vect-stmts.c:10999
0x1311e9b vect_transform_loop(_loop_vec_info*, gimple*)
        ../.././gcc/tree-vect-loop.c:9686
0x13416db try_vectorize_loop_1
        ../.././gcc/tree-vectorizer.c:1103
0x13418b7 try_vectorize_loop_1
        ../.././gcc/tree-vectorizer.c:1141
0x1342317 vectorize_loops()
        ../.././gcc/tree-vectorizer.c:1242
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.


FWIW, g++ works just fine with the slightly rewritten (e.g. do not use a local
variable) noboom.cpp

Based on my snapshots, the issue occurred first between 20210711 and 20210718
(I am now running a git bisect to point to a suspect commit)