[PATCH] D105020: [SLP]Improve graph reordering.

[Alexey Bataev via Phabricator via llvm-commits]

ABataev added a comment.

In D105020#2999765 <https://reviews.llvm.org/D105020#2999765>, @xbolva00 wrote:

> In D105020#2999752 <https://reviews.llvm.org/D105020#2999752>, @ABataev wrote:
>
>> In D105020#2975046 <https://reviews.llvm.org/D105020#2975046>, @goncharov wrote:
>>
>>> Here is a repro I found
>>>
>>>   $ cat ./repro.cc
>>>   #include <iostream>
>>>   namespace a {
>>>   __attribute__((noinline)) void b(uint8_t *c, float *d, uint16_t e, uint16_t f) {
>>>     uint16_t g = f;
>>>     uint16_t h = c[0] << 2 | c[4] & 3;
>>>     uint16_t l = c[1] << 2 | c[4] >> 2 & 3;
>>>     uint16_t v = c[2] << 2 | 3;
>>>     uint16_t j = c[3] << 2 | c[4] >> 6;
>>>     *(d - 1) = float(l - e) / g;
>>>     *(d - 2) = float(h - e) / g;
>>>     *(d - 3) = float(j - e) / g;
>>>     *(d - 4) = float(v - e) / g;
>>>   }
>>>   void bar(uint8_t *buffer, size_t k, size_t height, size_t, uint16_t e,
>>>            uint16_t f, float *m) {
>>>     int n = 24, g = f;
>>>     float *t = &m[(24 - 2) * 4];
>>>     size_t u = 2 * k;
>>>     for (int o; o < height; o++) {
>>>       uint8_t *p = buffer;
>>>       uint8_t *q = p;
>>>       float *r = &t[u];
>>>       for (int a = 0; a < u; a += 4) {
>>>         b(q, r, e, g);
>>>         r -= 4;
>>>       }
>>>       t -= n;
>>>     }
>>>   }
>>>   }  // namespace a
>>>   int main() {
>>>     uint8_t s[]{255, 0, 255, 0, 51};
>>>     float m[4 * 24]{};
>>>     a::bar(s, 4, 4, 0, 0, 1023, m);
>>>     int *out = reinterpret_cast<int *>(m);
>>>     int64_t sum;
>>>     for (int i = 0; i < sizeof(m) / sizeof(int); i++) sum += out[i];
>>>     std::cout << sum;
>>>   }
>>>   $ clang-before -O2 -std=gnu++17 repro.cc
>>>   $ ./a.out
>>>   17045651456
>>>   $ clang-after -O2 -std=gnu++17 repro.cc
>>>   $ ./a.out
>>>   16609148640
>>
>> Sorry, the reproducer is not correct. It has not initialized variables, writes after array bounds etc. Unable to use it as a reproducer for the investigation.
>
> So if they are not able to produce UB-free reproducer, you should recommit the patch.

I believe they have a reproducer and tried to reduce it but the tool just extracted/removed too much code here :). I'll try to check manually some parts of the code and wait for the actual reproducer, will recommit the patch in a couple of days if would not be able to find a bug/no correct reproducer provided.


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