[llvm-bugs] [Bug 43225] New: AVX miscompile at -O2 beginning with r360526

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43225

            Bug ID: 43225
           Summary: AVX miscompile at -O2 beginning with r360526
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: warren_ristow at playstation.sony.com
                CC: craig.topper at gmail.com, llvm-bugs at lists.llvm.org,
                    llvm-dev at redking.me.uk, spatel+llvm at rotateright.com

One of our random test-generators found a miscompile bug in an AVX test-case.
Bisecting identifies that the problem first appeared at r360526 (although it
isn't clear to me whether that commit has a bug, or is exposing a latent
bug -- by guess is it's exposing a problem).  I verified that the problem still
appears with a fairly modern version -- checked r370900.

Below is a somewhat reduced source-level repro.

$ cat test.cpp
// ==========================================================================
extern "C" int printf(const char *, ...);
typedef unsigned char uchar;
typedef double __attribute__((ext_vector_type(4))) double4;
typedef double __m256d __attribute__((__vector_size__(32), __aligned__(32)));
typedef double __m128d __attribute__((__vector_size__(16), __aligned__(16)));
typedef double __v2df __attribute__ ((__vector_size__ (16)));
typedef double __v4df __attribute__ ((__vector_size__ (32)));
typedef unsigned long long __v4du __attribute__ ((__vector_size__ (32)));

static void init(unsigned char pred, volatile void *data, unsigned size) {
  unsigned char *bytes = (unsigned char *)data;
  for (unsigned i = 0; i != size; ++i)
    bytes[i] = pred + i;
}

int main() {
  union { __m256d x; char c[32]; } zero_union;
  __m256d id6595;
  init(212, &id6595, sizeof(id6595));
  __m256d id6597;
  init(106, &id6597, sizeof(id6597));
  __m128d id6599;
  init(239, &id6599, sizeof(id6599));
  __m256d id1725 =
    __builtin_shufflevector((__v2df)id6599, (__v2df)id6599, 0, 1, -1, -1);
  zero_union.x = id1725;
  for (unsigned i = 16; i != 32; ++i)
    zero_union.c[i] = 0;
  __m256d id6598 = zero_union.x;
  __m256d id6596 = (__m256d) ((__v4df)id6597+(__v4df)id6598);
  __m256d id6594 =
    __builtin_shufflevector((__v4df)id6595, (__v4df)id6596, 1, 5, 1+2, 5+2);
  volatile __m256d id6600;
  init(176, &id6600, sizeof(id6600));
  volatile __m256d id6605;
  init(65, &id6605, sizeof(id6605));
  __m256d id6606;
  init(66, &id6606, sizeof(id6606));
  __m256d id6604 = (__m256d) (~(__v4du)id6605 & (__v4du)id6606);
  volatile __m256d id6609;
  init(168, &id6609, sizeof(id6609));
  __attribute__((aligned(32))) uchar id6613;
  init(124, &id6613, sizeof(id6613));
  __m256d id6610;
  init(217, &id6610, sizeof(id6610));
  for (uchar id6611_idx = 0; (id6611_idx < id6613); ++id6611_idx) {
    volatile __m256d id6612;
    init(93, &id6612, sizeof(id6612));
    id6610 *= id6612;
  }
  __m256d id6608 =
    __builtin_shufflevector((__v4df)id6609, (__v4df)id6610, 1, 5, 1+2, 5+2);
  static volatile __attribute__((aligned(2)))__m256d id6614 =
    __extension__ (__m256d){ 0, 0, 0, 0 };
  __m256d id6607 =
    (__m256d)__builtin_ia32_haddpd256((__v4df)id6608, (__v4df)id6614);
  __m256d id6603 =
    (__m256d)__builtin_ia32_hsubpd256((__v4df)id6604, (__v4df)id6607);
  volatile __m256d id6602 =
    __builtin_shufflevector((__v4df)id6603, (__v4df)id6603, 0, 0, 2, 2);
  volatile __attribute__((aligned(32)))__m256d id6601 =
    (__m256d)__builtin_ia32_sqrtpd256((__v4df)id6602);
  __m256d id6593 = (__m256d)__builtin_ia32_blendvpd256(
    (__v4df)id6594, (__v4df)id6600, (__v4df)id6601);
  double4 id6592 = (static_cast<double4>(id6593));
  printf("id6592:%lf %lf %lf %lf\n",id6592[0],id6592[1],id6592[2],id6592[3]);
  return 0;
}
// ==========================================================================
$ ~/llvm.8.0/bin/clang++ -mavx -O0 -o test.elf test.cpp
$ test.elf | tee llvm8.txt
id6592:-0.000000 -0.120083 -60539778500895675077088930481106321408.000000
-27866005112515140108039219831221433722840879450495184416280192272475975843840.000000
$ ~/llvm.8.0/bin/clang++ -mavx -O2 -o test.elf test.cpp
$ test.elf | diff llvm8.txt -
$ r360526/bin/clang++ --version | egrep 'version'\|'Target'
clang version 9.0.0 (trunk 360526)
Target: x86_64-unknown-linux-gnu
$ r360526/bin/clang++ -mavx -O0 -o test.elf test.cpp
$ test.elf | diff llvm8.txt -
$ r360526/bin/clang++ -mavx -O2 -o test.elf test.cpp
$ test.elf | diff llvm8.txt -
1c1
< id6592:-0.000000 -0.120083 -60539778500895675077088930481106321408.000000
-27866005112515140108039219831221433722840879450495184416280192272475975843840.000000
---
> id6592:-0.000000 -5141221720570257117792454033359263003807236078306659704678783633844346063763670599376596080887364908982157086903115200913387331142513248047145337233885905544954992509425426830156252708146824920980885521333040555469700954412883838074547909394193152829277777742490970125863264566428463469688215073724563456.000000 -60539778500895675077088930481106321408.000000 -27866005112515140108039219831221433722840879450495184416280192272475975843840.000000
$

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