Re: PATCH: PR middle-end/35897: DSE doesn't support targets with wide registers

[Eric Botcazou <ebotcazou at adacore dot com>]

> 1. positions_needed is long. But mask, which is int, is used on it.
> long may not be the same as int.  We haven't seen problems on x86
> so far since SSE register is 16byte which is less than size of int
> * 8.  This is no longer true for AVX register, which is 32byte.
> 2. A 4-byte integer should be able handle 32byte register. The only
> problem is DSE uses (1L << width) - 1) to set bits 0 to width - 1
> in a bitmask to 1. 1L << 32 doesn't work with 4byte integer.
>
> This patch changes int to long for mask and introduces a new function,
> fill_bitmask, to return a bitmask with bits 0 to width - 1 set to 1.
> fill_bitmask works with width from 1 to 32. Does it make sense?

Yes, but use 'unsigned HOST_WIDE_INT' for positions_needed, mask and the 
return value of the new helper routine, HOST_BITS_PER_WIDE_INT instead of 
sizeof * CHAR_BIT and remove the FIXME.

/* Return a bitmask with the first N low bits set.  */
 
static unsigned HOST_WIDE_INT
lowpart_bitmask (int n)
{
  unsigned HOST_WIDE_INT mask = ~(unsigned HOST_WIDE_INT) 0;
  return mask >> (HOST_BITS_PER_WIDE_INT - n);
}

OK with this change.

-- 
Eric Botcazou