ReallocShrink.C

// RUN: %cladclang %s -I%S/../../include -oReallocShrink.out 2>&1 | %filecheck %s
// RUN: ./ReallocShrink.out | %filecheck_exec %s

// Shrinking in-place realloc: the reverse sweep must resize the buffer (and its
// adjoint) back to the pre-realloc size so the pre-realloc reads stay in bounds
// and the adjoint accumulates correctly. Runs Memcheck-clean under the valgrind
// CI row.

#include "clad/Differentiator/Differentiator.h"
#include <cstdlib>

// res = (x + x*x) + x  ->  dres/dx = 2 + 2x ; at x = 3 -> 8
double shrink_realloc(double x) {
  double* p = (double*)malloc(2 * sizeof(double));
  p[0] = x;
  p[1] = x * x;
  double res = p[0] + p[1];
  p = (double*)realloc(p, 1 * sizeof(double)); // shrink 2 -> 1
  res += p[0];
  free(p);
  return res;
}

int main() {
  auto g = clad::gradient<clad::opts::disable_tbr>(shrink_realloc, "x");
  double dx = 0;
  g.execute(3.0, &dx);
  printf("{%.2f}\n", dx); // CHECK-EXEC: {8.00}
}