[PATCH] D46163: [DO NOT SUBMIT] Do strlen() while computing xxhash

[George Rimar via Phabricator via llvm-commits]

grimar added inline comments.


================
Comment at: llvm/lib/Support/xxhash.cpp:149
+    if (uint64_t X = (R[0] - 0x0101010101010101) & ~R[0] & 0x8080808080808080) {
+      Remaining = (__builtin_ffsl(X) >> 3) - 1;
+      break;
----------------
I tried to build this patch with MSVS, but it complains about the absence of this function.

I had to use the following instead:

```
int psnip_builtin_ffsl(long v) {
  unsigned long r;
  if (_BitScanForward(&r, (unsigned long)v)) {
    return (int)(r + 1);
  }
  return 0;
}
```
(took it from https://github.com/nemequ/portable-snippets/tree/master/builtin).

But it does not work correctly it seems. I am testing on `lld-speed-test\lld-speed-test\scylla`,
here at some point `Remaining` becomes (-1). And then lines below (185, 186) 

```
  const char *End = Q + Remaining;
  size_t Len = End - P;
```

handle it wrong and code ends up with
an infinite loop in `splitStrings1` because `strlen_xxHash64` returns -1 always.




https://reviews.llvm.org/D46163