On 10/19/21 12:28, Jakub Jelinek wrote:
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.
Yes, my WIP patchset has:
((unsigned HOST_WIDE_INT) -(((object_size_type & MIN_BIT) >> 1) ^ 1));
which results in:
xorl %eax, %eax
andl $2, %edi
sete %al
negq %rax
-/* 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;
OK, I'll send an updated patch.
Thanks,
Siddhesh
