@@ -27,21 +27,24 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
u64 temp64 = (__force u64)sum;
unsigned result;
- while (unlikely(len >= 64)) {
- asm("addq 0*8(%[src]),%[res]\n\t"
- "adcq 1*8(%[src]),%[res]\n\t"
- "adcq 2*8(%[src]),%[res]\n\t"
- "adcq 3*8(%[src]),%[res]\n\t"
- "adcq 4*8(%[src]),%[res]\n\t"
- "adcq 5*8(%[src]),%[res]\n\t"
- "adcq 6*8(%[src]),%[res]\n\t"
- "adcq 7*8(%[src]),%[res]\n\t"
- "adcq $0,%[res]"
- : [res] "+r" (temp64)
- : [src] "r" (buff)
- : "memory");
- buff += 64;
- len -= 64;
+ if (unlikely(len >= 64)) {
+ const void *lim = buff + (len & ~63u);
+ do {
+ asm("addq 0*8(%[src]),%[res]\n\t"
+ "adcq 1*8(%[src]),%[res]\n\t"
+ "adcq 2*8(%[src]),%[res]\n\t"
+ "adcq 3*8(%[src]),%[res]\n\t"
+ "adcq 4*8(%[src]),%[res]\n\t"
+ "adcq 5*8(%[src]),%[res]\n\t"
+ "adcq 6*8(%[src]),%[res]\n\t"
+ "adcq 7*8(%[src]),%[res]\n\t"
+ "adcq $0,%[res]"
+ : [res] "+r" (temp64)
+ : [src] "r" (buff)
+ : "memory");
+ asm("" : "+r" (buff));
+ buff += 64;
+ } while (buff < lim);
}
if (len & 32) {
gcc converts the loop into one that only increments the pointer but makes a mess of calculating the limit and gcc 9.1+ completely refuses to use the final value of 'buff' from the last iteration. Explicitly code a pointer comparison and don't bother changing len. Signed-off-by: David Laight <david.laight@aculab.com> --- The asm("" : "+r" (buff)); forces gcc to use the loop-updated value of 'buff' and removes at least 6 instructions. The gcc folk really ought to look at why gcc 9.1 onwards is so much worse that gcc 8. See https://godbolt.org/z/T39PcnvfE arch/x86/lib/csum-partial_64.c | 33 ++++++++++++++++++--------------- 1 file changed, 18 insertions(+), 15 deletions(-)