PVS-Studio warning V629 for Snes9x

static inline int64 SAR (const int64 b, const int n)
{
#ifndef RIGHTSHIFT_int64_IS_SAR
  if (b < 0)
    return ((b >> n) | (-1 << (64 - n)));
#endif
  return (b >> n);
}

This suspicious code was found in Snes9x project by PVS-Studio static code analyzer.
Warning message is:
V629 Consider inspecting the '- 1 << (64 - n)' expression. Bit shifting of the 32-bit value with a subsequent expansion to the 64-bit type. sar.h 217

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