On Tue, Oct 19, 2021 at 09:47:45AM +0530, Siddhesh Poyarekar wrote:
> Compute the unknown size value as a function of the min/max bit of
> object_size_type. This transforms into a neat little branchless
> sequence on x86_64:
>
> movl %edi, %eax
> sarl %eax
> xorl $1, %eax
> negl %eax
> cltq
>
> which should be faster than loading the value from memory. A quick
> unscientific test using
>
> `time make check-gcc RUNTESTFLAGS="dg.exp=builtin*"`
But if you use some other higher bit of object_size_type for the mode
(normal vs. dynamic) you'd need to mask it away, so it will become longer.
Anyway, I guess that part is ok.
> -/* Compute object_sizes for PTR, defined to an unknown value. */
> -
> -static void
> -unknown_object_size (struct object_size_info *osi, tree ptr)
> -{
> - int object_size_type = osi->object_size_type;
> - unsigned int varno = SSA_NAME_VERSION (ptr);
> - unsigned HOST_WIDE_INT bytes;
> -
> - gcc_assert (object_sizes[object_size_type][varno]
> - != unknown[object_size_type]);
> - gcc_assert (osi->pass == 0);
> -
> - bytes = unknown[object_size_type];
> -
> - if ((object_size_type & 2) == 0)
> - {
> - if (object_sizes[object_size_type][varno] < bytes)
> - object_sizes[object_size_type][varno] = bytes;
> - }
> - else
> - {
> - if (object_sizes[object_size_type][varno] > bytes)
> - object_sizes[object_size_type][varno] = bytes;
> - }
> -}
But I don't think removing this function is desirable.
Can it be greatly simplified? Yes, certainly.
The assert verifies it is not unknown before, and then for mode 0 or 1
uses maximum which will always be unknown and for mode 2 or 3
minimum which will always be unknown as well.
But I'd keep the asserts in there. So it can become
int object_size_type = osi->object_size_type;
unsigned int varno = SSA_NAME_VERSION (ptr);
unsigned HOST_WIDE_INT bytes = unknown (object_size_type);
gcc_checking_assert (object_sizes[object_size_type][varno] != bytes);
gcc_checking_assert (osi->pass == 0);
object_sizes[object_size_type][varno] = bytes;
Jakub
