isl_union_map_coalesce sub-optimally merges 4 pieces in 'test' to 2 pieces. A simpler 1 piece solution is 'orig_simplified'

isl_union_map_coalesce_inefficient.c

#include <stdio.h>
#include <stdlib.h>
#include "isl/flow.h"
#include "isl/ctx.h"
#include "isl/val.h"
#include "isl/set.h"
#include "isl/map.h"
#include "isl/union_map.h"
#include "isl/union_set.h"
#include "isl/flow.h"
#include "isl/schedule.h"
#include "string.h"
#include "assert.h"

#define PRINT(name, obj) {isl_printer_start_line(printer); \
  isl_printer_print_str(printer, "\n\n" #obj ":\n----\n"); \
  isl_printer_print_##name(printer, obj); isl_printer_end_line(printer);}


int main() {
  isl_ctx *ctx = isl_ctx_alloc();
  isl_printer *printer = isl_printer_to_str(ctx);

  isl_union_map *test = isl_union_map_read_from_str(ctx, "{ Stmt_loop_body_reduction[i0, i1] -> MemRef_retval[o0, o1] : (i0 = 1 and i1 = 1 and o0 = 1 and o1 = 1) or (i0 = 0 and i1 = 1 and o0 = 0 and o1 = 1) or (i0 = 1 and i1 = 0 and o0 = 1 and o1 = 0) or (i0 = 0 and i1 = 0 and o0 = 0 and o1 = 0) } ");

  PRINT(union_map, test);
  char *test_str = isl_printer_get_str(printer);
  printf("%s", test_str);
  isl_printer_flush(printer);

  isl_union_map *simplified = isl_union_map_coalesce(test);
  PRINT(union_map, simplified);
  char *simplified_str = isl_printer_get_str(printer);
  printf("%s", simplified_str);

  isl_union_map *orig_simplified = isl_union_map_read_from_str(ctx, "{ Stmt_loop_body_reduction[i0, i1] -> MemRef_retval[o0, o1] : ( 0 <= i0 <=1 and 0 <= i1 <=1 and o0 = i0 and o1 = i1 ) }");
  assert(isl_bool_true == isl_union_map_is_equal(simplified, orig_simplified));

  return 0;
}

Output:

test:
----
{ Stmt_loop_body_reduction[i0 = 1, i1 = 1, i2 = 783] -> MemRef_retval[o0 = 1, o1 = 1]; Stmt_loop_body_reduction[i0 = 0, i1 = 1, i2 = 783] -> MemRef_retval[o0 = 0, o1 = 1]; Stmt_loop_body_reduction[i0 = 1, i1 = 0, i2 = 783] -> MemRef_retval[o0 = 1, o1 = 0]; Stmt_loop_body_reduction[i0 = 0, i1 = 0, i2 = 783] -> MemRef_retval[o0 = 0, o1 = 0] }


simplified:
----
{ Stmt_loop_body_reduction[i0, i1, i2 = 783] -> MemRef_retval[o0 = i0, o1 = i1] : i0 >= 0 and 0 <= i1 <= 1 - i0; Stmt_loop_body_reduction[i0 = 1, i1 = 1, i2 = 783] -> MemRef_retval[o0 = 1, o1 = 1] }

(Assertion is satisfied - hence, it can be further simplified).