[ICE] Propagate_necessity for stream refs

[IgWod]

The following program fails to compile with an internal compiler error:

#include <stdio.h>
#include <stdlib.h>
#include "../common/common.h"
#include "../common/sync.h"

int main()
{
  double sleft[2] __attribute__((stream));
  void* sleft_ref = malloc(2*sizeof(void*));
  memcpy(sleft_ref, sleft, 2*sizeof(void*));

  double scenter[2] __attribute__((stream));
  void* scenter_ref = malloc(2*sizeof(void*));
  memcpy(scenter_ref, scenter, 2*sizeof(void*));

  double sright[2] __attribute__((stream));
  void* sright_ref = malloc(2*sizeof(void*));
  memcpy(sright_ref, sright, 2*sizeof(void*));

  double input[12] = {1,1,1,1,1,1,1,1,1,1,1,1};
  double* input_ref = input;

  double output[12];
  double* output_ref = output;

  for(int id = 0; id < 2; id++)
  {
    double left_out[1];
    double center_out[5];
    double right_out[1];

    #pragma omp task output(sleft_ref[id] << left_out[1], \
                            scenter_ref[id] << center_out[5], \
                            sright_ref[id] << right_out[1])
    {
      left_out[0] = input_ref[id * 5];
      for(int i = 0; i < 5; i++)
        center_out[i] = input_ref[id * 5 + i + 1];
      right_out[0] = input_ref[id * 5 + 6];
    }
  }

  for(int id = 0; id < 2; id++)
  {
    double left_in[1];
    double center_in[5];
    double right_in[1];

    #pragma omp task input(sleft_ref[id] >> left_in[1], \
                           scenter_ref[id] >> center_in[5], \
                           sright_ref[id] >> right_in[1])
    {
      output_ref[id * 5 + 1] = (left_in[0] + center_in[0] + center_in[1]) / 3.0;
      for(int i = 1; i < 4; i++)
        output_ref[id * 5 + i + 1] = (center_in[i - 1] + center_in[i] + center_in[i + 1]) / 3.0;
      output_ref[id * 5 + 5] = (right_in[0] + center_in[3] + center_in[4]) / 3.0;
    }
  }

  #pragma omp taskwait

  for(int i = 0; i < 10; i++)
    printf("%lf ", output[i + 1]);
  printf("\n");
}

The following error is generated:

during GIMPLE pass: cddce
stream_simple.c:69:1: internal compiler error: in propagate_necessity, at tree-ssa-dce.c:902
   69 | }
      | ^
0xb648ce propagate_necessity
        ../../gcc/tree-ssa-dce.c:902
0xb648ce perform_tree_ssa_dce
        ../../gcc/tree-ssa-dce.c:1592

The problem does not appear when stream references are declared outside the main function:

void* sleft_ref;
void* scenter_ref;
void* sright_ref;

int main()
{
  double sleft[2] __attribute__((stream));
  sleft_ref = malloc(2*sizeof(void*));
  memcpy(sleft_ref, sleft, 2*sizeof(void*));

  double scenter[2] __attribute__((stream));
  scenter_ref = malloc(2*sizeof(void*));
  memcpy(scenter_ref, scenter, 2*sizeof(void*));

  double sright[2] __attribute__((stream));
  sright_ref = malloc(2*sizeof(void*));
  memcpy(sright_ref, sright, 2*sizeof(void*));

[nmnobre]

If compiled with -fno-tree-dce, you get an extra gift: a beautiful, chocolate-glazed segmentation fault 🙃