[Bug tree-optimization/99220] New: [11 Regression] ICE during vectorization when multiple instances do the same calculation but have different num lanes

[tnfchris at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99220

            Bug ID: 99220
           Summary: [11 Regression] ICE during vectorization when multiple
                    instances do the same calculation but have different
                    num lanes
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Keywords: ice-on-valid-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: tnfchris at gcc dot gnu.org
          Reporter: tnfchris at gcc dot gnu.org
  Target Milestone: ---
            Target: aarch64-*

The following testcase

class a {
  float b;
  float c;

public:
  a(float d, float e) : b(d), c(e) {}
  a operator+(a d) { return a(b + d.b, c + d.c); }
  a operator-(a d) { return a(b - d.b, c - d.c); }
  a operator*(a d) { return a(b * b - c * c, b * c + c * d.b); }
};
long f;
a *g;
class {
  a *h;
  long i;
  a *j;

public:
  void k() {
    a l = h[0], m = g[i], n = l * g[1], o = l * j[8];
    g[i] = m + n;
    g[i + 1] = m - n;
    j[f] = o;
  }
} p;
main() { p.k(); }

crashes with aarch64-none-elf-g++ -w -march=armv8.3-a -O3 -S main.cpp

because two nodes end up with the same pointer. During the loop that analyzes
all the instances during optimize_load_redistribution_1 we do

      if (value)
        {
          SLP_TREE_REF_COUNT (value)++;
          SLP_TREE_CHILDREN (root)[i] = value;
          vect_free_slp_tree (node);
        }

when doing a replacement.  When this is done and the refcount for the node
reaches 0, the node is removed, which allows the libc to return the pointer
again in the next call to new, which it does..


First instance

note:   node 0x5325f48 (max_nunits=1, refcnt=2)
note:   op: VEC_PERM_EXPR
note:           { }
note:           lane permutation { 0[0] 1[1] 0[2] 1[3] }
note:           children 0x5325db0 0x5325200

Second instance

note:   node 0x5325f48 (max_nunits=1, refcnt=1)
note:   op: VEC_PERM_EXPR
note:           { }
note:           lane permutation { 0[0] 1[1] }
note:           children 0x53255b8 0x5325530

This will end up with the illegal construction of

note:   node 0x53258e8 (max_nunits=2, refcnt=2)
note:   op template: slp_patt_57 = .COMPLEX_MUL (_16, _16);
note:           stmt 0 _16 = _14 - _15;
note:           stmt 1 _23 = _17 + _22;
note:           children 0x53257d8 0x5325d28
note:   node 0x53257d8 (max_nunits=2, refcnt=3)
note:   op template: l$b_4 = MEM[(const struct a &)_3].b;
note:           stmt 0 l$b_4 = MEM[(const struct a &)_3].b;
note:           stmt 1 l$c_5 = MEM[(const struct a &)_3].c;
note:           load permutation { 0 1 }
note:   node 0x5325d28 (max_nunits=2, refcnt=8)
note:   op template: l$b_4 = MEM[(const struct a &)_3].b;
note:           stmt 0 l$b_4 = MEM[(const struct a &)_3].b;
note:           stmt 1 l$c_5 = MEM[(const struct a &)_3].c;
note:           stmt 2 l$b_4 = MEM[(const struct a &)_3].b;
note:           stmt 3 l$c_5 = MEM[(const struct a &)_3].c;
note:           load permutation { 0 1 0 1 }

To prevent this we need to add these temporary VEC_PERM_EXPR nodes to the
bst_map cache and increase their refcnt one more.