[llvm-dev] Problem with clang optimizer?
Craig Topper via llvm-dev
llvm-dev at lists.llvm.org
Sat Sep 25 09:06:31 PDT 2021
It reproduced for me with -march=nehalem which does not have AVX.
On Sat, Sep 25, 2021 at 2:51 AM Dimitry Andric via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> It is only occurring (as far as I can see now) on x86_64, with -mavx
> enabled. Or with a target CPU that supports AVX. And it is not Apple clang
> specific.
>
> -Dimitry
>
> On 24 Sep 2021, at 15:30, Blumenthal, Uri - 0553 - MITLL via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> I tried to reproduce it on goldbolt with clang 12.0.0 and 12.0.1 but
> things seem fine when I run it there: https://godbolt.org/z/vrq8j6Kj7.
> Can you share your exact clang invocation? Does it only reproduce in some
> specific environment?
>
> Save the source I posted before into “sha3-reproducer.cxx” file. Let me
> know if you want it re-posted here.
>
> $ clang++-mp-12 -v
> clang version 12.0.1
> Target: x86_64-apple-darwin20.6.0
> Thread model: posix
> InstalledDir: /opt/local/libexec/llvm-12/bin
> $ clang++-mp-12 -o s -O3 sha3-reproducer.cxx
> $ ./s
> Assertion failed: (T[0] == 16394434931424703552u), function main, file
> sha3-reproducer.cxx, line 103.
> Abort trap: 6
> $ clang++-mp-12 -o s -O2 sha3-reproducer.cxx
> $ ./s
> Assertion failed: (T[0] == 16394434931424703552u), function main, file
> sha3-reproducer.cxx, line 103.
> Abort trap: 6
> $ clang++-mp-12 -o s -O1 sha3-reproducer.cxx
> $ ./s
> $
>
> Clang-12 is installed via Macports, which is why we invoke the executable
> as clang++-mp-12.
>
> The same problem manifests in exactly the same way in the Xcode-13 version
> of Clang (presumably based on LLVM Clang-12).
>
> I’ll be happy to provide more of specific details, if you let me know what
> you need.
>
>
> Also, it generally helps to reduce code bug reports as much as possible;
> creduce can help with that: https://embed.cs.utah.edu/creduce/using/.
>
> Understood. Unfortunately, the above reproducer is the best we could come
> up with. An alternative is trying to build the Botan package itself
> https://github.com/randombit/botan.git.
>
>
>
>
> On Thu, Sep 23, 2021 at 10:14 PM Blumenthal, Uri - 0553 - MITLL via
> llvm-dev <llvm-dev at lists.llvm.org> wrote:
>
> I’m not sure if this is the correct list, so please direct me to the right
> one if this bug report shouldn’t go here.
>
> The problem is: invoking clang (v12) with -O2 or better optimization flags
> generates wrong object code for the following C++. Compiling it with -O1
> generates working binary.
>
>
> =================
>
> #include <cstdint>
> #include <cassert>
>
> template<size_t ROT, typename T>
> inline constexpr T rotl(T input)
> {
> static_assert(ROT > 0 && ROT < 8*sizeof(T), "Invalid rotation
> constant");
> return static_cast<T>((input << ROT) | (input >> (8*sizeof(T) - ROT)));
> }
>
> inline void SHA3_round(uint64_t T[25], const uint64_t A[25], uint64_t RC)
> {
> const uint64_t C0 = A[0] ^ A[5] ^ A[10] ^ A[15] ^ A[20];
> const uint64_t C1 = A[1] ^ A[6] ^ A[11] ^ A[16] ^ A[21];
>
> // the calculation of C2 fails for -O3 or -O2 with clang 12
> // FWIW: it would produce a value that doesn't fit into a _signed_
> 64-bit int
> const uint64_t C2 = A[2] ^ A[7] ^ A[12] ^ A[17] ^ A[22];
>
> const uint64_t C3 = A[3] ^ A[8] ^ A[13] ^ A[18] ^ A[23];
> const uint64_t C4 = A[4] ^ A[9] ^ A[14] ^ A[19] ^ A[24];
>
> const uint64_t D0 = rotl<1>(C0) ^ C3;
> const uint64_t D1 = rotl<1>(C1) ^ C4;
> const uint64_t D2 = rotl<1>(C2) ^ C0;
> const uint64_t D3 = rotl<1>(C3) ^ C1;
> const uint64_t D4 = rotl<1>(C4) ^ C2;
>
> const uint64_t B00 = A[ 0] ^ D1;
> const uint64_t B01 = rotl<44>(A[ 6] ^ D2);
> const uint64_t B02 = rotl<43>(A[12] ^ D3);
> const uint64_t B03 = rotl<21>(A[18] ^ D4);
> const uint64_t B04 = rotl<14>(A[24] ^ D0);
> T[ 0] = B00 ^ (~B01 & B02) ^ RC;
> T[ 1] = B01 ^ (~B02 & B03);
> T[ 2] = B02 ^ (~B03 & B04);
> T[ 3] = B03 ^ (~B04 & B00);
> T[ 4] = B04 ^ (~B00 & B01);
>
> const uint64_t B05 = rotl<28>(A[ 3] ^ D4);
> const uint64_t B06 = rotl<20>(A[ 9] ^ D0);
> const uint64_t B07 = rotl< 3>(A[10] ^ D1);
> const uint64_t B08 = rotl<45>(A[16] ^ D2);
> const uint64_t B09 = rotl<61>(A[22] ^ D3);
> T[ 5] = B05 ^ (~B06 & B07);
> T[ 6] = B06 ^ (~B07 & B08);
> T[ 7] = B07 ^ (~B08 & B09);
> T[ 8] = B08 ^ (~B09 & B05);
> T[ 9] = B09 ^ (~B05 & B06);
>
> // --- instructions starting from here can be removed
> // and the -O3 dicrepancy is still triggered
>
> const uint64_t B10 = rotl< 1>(A[ 1] ^ D2);
> const uint64_t B11 = rotl< 6>(A[ 7] ^ D3);
> const uint64_t B12 = rotl<25>(A[13] ^ D4);
> const uint64_t B13 = rotl< 8>(A[19] ^ D0);
> const uint64_t B14 = rotl<18>(A[20] ^ D1);
> T[10] = B10 ^ (~B11 & B12);
> T[11] = B11 ^ (~B12 & B13);
> T[12] = B12 ^ (~B13 & B14);
> T[13] = B13 ^ (~B14 & B10);
> T[14] = B14 ^ (~B10 & B11);
>
> const uint64_t B15 = rotl<27>(A[ 4] ^ D0);
> const uint64_t B16 = rotl<36>(A[ 5] ^ D1);
> const uint64_t B17 = rotl<10>(A[11] ^ D2);
> const uint64_t B18 = rotl<15>(A[17] ^ D3);
> const uint64_t B19 = rotl<56>(A[23] ^ D4);
> T[15] = B15 ^ (~B16 & B17);
> T[16] = B16 ^ (~B17 & B18);
> T[17] = B17 ^ (~B18 & B19);
> T[18] = B18 ^ (~B19 & B15);
> T[19] = B19 ^ (~B15 & B16);
>
> const uint64_t B20 = rotl<62>(A[ 2] ^ D3);
> const uint64_t B21 = rotl<55>(A[ 8] ^ D4);
> const uint64_t B22 = rotl<39>(A[14] ^ D0);
> const uint64_t B23 = rotl<41>(A[15] ^ D1);
> const uint64_t B24 = rotl< 2>(A[21] ^ D2);
> T[20] = B20 ^ (~B21 & B22);
> T[21] = B21 ^ (~B22 & B23);
> T[22] = B22 ^ (~B23 & B24);
> T[23] = B23 ^ (~B24 & B20);
> T[24] = B24 ^ (~B20 & B21);
> }
>
> int main()
> {
> uint64_t T[25];
>
> uint64_t A[25] = {
> 15515230172486u, 9751542238472685244u, 220181482233372672u,
> 2303197730119u, 9537012007446913720u, 0u, 14782389640143539577u,
> 2305843009213693952u, 1056340403235818873u, 16396894922196123648u,
> 13438274300558u, 3440198220943040u, 0u, 3435902021559310u, 64u,
> 14313837075027532897u, 32768u, 6880396441885696u,
> 14320469711924527201u,
> 0u, 9814829303127743595u, 18014398509481984u,
> 14444556046857390455u,
> 4611686018427387904u, 18041275058083100u };
>
> SHA3_round(T, A, 0x0000000000008082);
>
> assert(T[0] == 16394434931424703552u);
> assert(T[1] == 10202638136074191489u);
> assert(T[2] == 6432602484395933614u);
> assert(T[3] == 10616058301262943899u);
> assert(T[4] == 14391824303596635982u);
> assert(T[5] == 5673590995284149638u);
> assert(T[6] == 15681872423764765508u);
> assert(T[7] == 11470206704342013341u);
> assert(T[8] == 8508807405493883168u);
> assert(T[9] == 9461805213344568570u);
> assert(T[10] == 8792313850970105187u);
> assert(T[11] == 13508586629627657374u);
> assert(T[12] == 5157283382205130943u);
> assert(T[13] == 375019647457809685u);
> assert(T[14] == 9294608398083155963u);
> assert(T[15] == 16923121173371064314u);
> assert(T[16] == 4737739424553008030u);
> assert(T[17] == 5823987023293412593u);
> assert(T[18] == 13908063749137376267u);
> assert(T[19] == 13781177305593198238u);
> assert(T[20] == 9673833001659673401u);
> assert(T[21] == 17282395057630454440u);
> assert(T[22] == 12906624984756985556u);
> assert(T[23] == 3081478361927354234u);
> assert(T[24] == 93297594635310132u);
>
> return 0;
> }
> =================
>
> Your help debugging and fixing this problem is appreciated!
> --
> Regards,
> Uri Blumenthal Voice: (781) 981-1638
> Secure Resilient Systems and Technologies Cell: (339) 223-5363
> MIT Lincoln Laboratory
> 244 Wood Street, Lexington, MA
> <https://www.google.com/maps/search/Wood+Street,+Lexington,+MA+02420-9108?entry=gmail&source=g>
> 02420-9108
> <https://www.google.com/maps/search/Wood+Street,+Lexington,+MA+02420-9108?entry=gmail&source=g>
>
>
> Web: https://www.ll.mit.edu/biographies/uri-blumenthal
> Root CA: https://www.ll.mit.edu/llrca2.pem
>
> *There are two ways to design a system. One is to make is so simple there
> are obviously no deficiencies.*
> *The other is to make it so complex there are no obvious deficiencies.*
> *
> -
> C. A. R. Hoare*
>
> _______________________________________________
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>
>
> --
> Jakub Kuderski
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>
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>
--
~Craig
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