[Bug tree-optimization/94784] New: ICE: in simplify_vector_constructor, at tree-ssa-forwprop.c:2482

[felix.yang at huawei dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94784

            Bug ID: 94784
           Summary: ICE: in simplify_vector_constructor, at
                    tree-ssa-forwprop.c:2482
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: felix.yang at huawei dot com
  Target Milestone: ---
            Target: aarch64

I see one gcc_assert was introduce in: 
https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544271.html

It looks like this is causing an ICE when compiling the foo.c test.
Gimple input to forwprop4 pass looks like:
pass_v4hi (v4hi v)
{
  vector(4) short int * vectp.4;
  vector(4) short int * vectp_a.3;
  union u4hi u;
  int j;
  short int _2;
  short int _3;
  vector(4) short int _6;
  short int _25;
  short int _26;

  <bb 2> [local count: 214748368]:
  _3 = BIT_FIELD_REF <v_5(D), 16, 0>;
  _2 = BIT_FIELD_REF <v_5(D), 16, 16>;
  _26 = BIT_FIELD_REF <v_5(D), 16, 32>;
  _25 = BIT_FIELD_REF <v_5(D), 16, 48>;
  _6 = {_3, _2, _26, _25};                                                     
 <========
  MEM <vector(4) short int> [(short int *)&a] = _6;  <========
  u ={v} {CLOBBER};
  return;
}

Here at the crash site, we have two vector types with different modes:

(gdb) p debug_tree (src_type)
 <vector_type 0xffffb20f73f0 v4hi
    type <integer_type 0xffffb22ea498 short int sizes-gimplified HI
        size <integer_cst 0xffffb22d0f48 constant 16>
        unit-size <integer_cst 0xffffb22d0f60 constant 2>
        align:16 warn_if_not_align:0 symtab:0 alias-set 2 canonical-type
0xffffb22ea498 precision:16 min <integer_cst 0xffffb22d0f00 -32768> max
<integer_cst 0xffffb22d0f18 32767>
        pointer_to_this <pointer_type 0xffffb240f000>>
    sizes-gimplified V4HI
    size <integer_cst 0xffffb22d0d98 type <integer_type 0xffffb22ea0a8
bitsizetype> constant 64>
    unit-size <integer_cst 0xffffb22d0db0 type <integer_type 0xffffb22ea000
sizetype> constant 8>
    align:64 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0xffffb23b1690 nunits:4 context <translation_unit_decl 0xffffb20f68e8 foo.c>>
$5 = void

(gdb) p debug_tree (type)
 <vector_type 0xffffb20f7348
    type <integer_type 0xffffb22ea498 short int sizes-gimplified HI
        size <integer_cst 0xffffb22d0f48 constant 16>
        unit-size <integer_cst 0xffffb22d0f60 constant 2>
        align:16 warn_if_not_align:0 symtab:0 alias-set 2 canonical-type
0xffffb22ea498 precision:16 min <integer_cst 0xffffb22d0f00 -32768> max
<integer_cst 0xffffb22d0f18 32767>
        pointer_to_this <pointer_type 0xffffb240f000>>
    VNx2HI
    size <integer_cst 0xffffb22d0d98 type <integer_type 0xffffb22ea0a8
bitsizetype> constant 64>
    unit-size <integer_cst 0xffffb22d0db0 type <integer_type 0xffffb22ea000
sizetype> constant 8>
    align:64 warn_if_not_align:0 symtab:0 alias-set -1 canonical-type
0xffffb23b1690 nunits:4
    pointer_to_this <pointer_type 0xffffb20f77e0>>
$6 = void

foo.c
typedef short __attribute__((vector_size (8))) v4hi; typedef union U4HI { v4hi
v; short a[4]; } u4hi;

short a[4];

void pass_v4hi (v4hi v) {
    int j;
    u4hi u;
    u.v = v;
    for (j = 0; j < 4; j++)
      a[j] = u.a[j];
};

$ aarch64-linux-gnu-gcc -S -O2 -ftree-slp-vectorize -march=armv8.2-a+sve
-msve-vector-bits=256 foo.c during GIMPLE pass: forwprop dump file:
foo.c.190t.forwprop4
foo.c: In function ‘pass_v4hi’:
foo.c:7:6: internal compiler error: in simplify_vector_constructor, at
tree-ssa-forwprop.c:2482
    7 | void pass_v4hi (v4hi v) {
      |      ^~~~~~~~~
0x147dbf7 simplify_vector_constructor
        ../../gcc-git/gcc/tree-ssa-forwprop.c:2482
0x1480a2b execute
        ../../gcc-git/gcc/tree-ssa-forwprop.c:3151