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Re: [PATCH] Make BITMAP_WORD more easily configurable


On 7/31/19 4:00 AM, Richard Biener wrote:
On Tue, 30 Jul 2019, Martin Sebor wrote:

On 7/30/19 9:19 AM, Jakub Jelinek wrote:
On Tue, Jul 30, 2019 at 09:16:45AM -0600, Martin Sebor wrote:
Say something like this POC:

We have those already, see ctz_hwi, clz_hwi etc.
The thing is that BITMAP_WORD isn't always the same type as unsigned
HOST_WIDE_INT, and so we need ones with the BITMAP_WORD type.

That sounds like a problem overloading would solve to the benefit
of all clients.  I.e., overload count_trailing_zeros (or whatever
other name) to take integer arguments of all widths (signed and
unsigned) and call the appropriate built-in from each.  That way
we just have to remember one function name and know that it will
be the right choice regardless of the type of the argument.

The problem with clz at least is that you have to make sure
to only allow overloads to exactly match the type of the
operand since semantics change once you do any promotion.
For popcount and ctz that's only an issue for signed arguments,
but still.

And I don't see any optimization of (uint){clzl,popcountl}((ulong)uintvar)
-> {clz,popcount} (uintvar)

unsigned int foo (unsigned int x)
{
   unsigned long y = x;
   unsigned long z = __builtin_popcountl (y);
   return z;
}

calls __popcountdi2 for me.

So if you dislike the macros then we could add
{popcount,clz,ctz}_bitmap_word () functions.

Still having the plumbing in once place looks like an improvement
to me - not sure if your comments were an objection to the original
patch?

Not an objection, just as an encouragement to consider going
the wrapper route you mentioned.  I think that would make
for a more broadly applicable improvement with a more user
friendly interface than what's available today.

Martin


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