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From: "vsevolod.livinskij at frtk dot ru" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/102622] New: Wrong code with -O3 for
 skylake-avx512 and icelake-server
Date: Tue, 05 Oct 2021 19:37:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102622

            Bug ID: 102622
           Summary: Wrong code with -O3 for skylake-avx512 and
                    icelake-server
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vsevolod.livinskij at frtk dot ru
  Target Milestone: ---

Reproducer:
// func.cpp
#include <algorithm>

extern int var_20, var_22;
extern short arr_32[];
extern char arr_45[];

void test(int a, unsigned b, long long *c) {
  for (short d =3D 0; d < 13; d++) {
    for (int e =3D 0; e < a; e +=3D 3)
      var_20 =3D 0;
    if (std::max(b, unsigned((short)b))) {
      arr_32[d] =3D 0;
      var_22 =3D *c;
    }
    for (unsigned f =3D 0; f < 69; f +=3D 4)
      arr_45[f] =3D 0;
  }
}

driver.cpp
#include <stdio.h>

unsigned long long int a =3D 10693271954245845448ULL;
unsigned int b =3D 1144022456U;
long long int c =3D 42;
int var_20 =3D 0;
long long int var_22 =3D 0;
unsigned short arr_32 [13];
unsigned char arr_45 [69];

void test(int a, unsigned int b, long long int* c);

int main() {
    test(a, b, &c);
    printf("%llu\n", var_22);
}

Error:
>$ g++ -O3 -march=3Dskylake-avx512 func.cpp driver.cpp && sde -skx -- ./a.o=
ut=20
0
>$ g++ -O2 -march=3Dskylake-avx512 func.cpp driver.cpp && sde -skx -- ./a.o=
ut=20
42

GCC version:
Using built-in specs.
COLLECT_GCC=3Dg++
COLLECT_LTO_WRAPPER=3D/testing/gcc/bin/libexec/gcc/x86_64-pc-linux-gnu/12.0=
.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /testing/gcc/gcc_src/configure --enable-multilib
--prefix=3D/testing/gcc/bin --disable-bootstrap
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20211004 (154fd0896ef22fcf5235e35e2b795394dddd7a33) (GCC=
)=