Use a simple logical shift and increment to calculate the number of slots
taken by the DMA segment boundary.
At least GCC-13 is not able to optimize the expression, producing this
horrible assembly code on x86:
cmpq $-1, %rcx
je .L364
addq $2048, %rcx
shrq $11, %rcx
movq %rcx, %r13
.L331:
// rest of the function here...
// after function epilogue and return:
.L364:
movabsq $9007199254740992, %r13
jmp .L331
After the optimization, the code looks more reasonable:
shrq $11, %r11
leaq 1(%r11), %rbx
Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
d069ed288a