[llvm-bugs] [Bug 41721] New: gvn produces wrong code with "opt -inline -mem2reg -instcombine -licm -reg2mem -memcpyopt -gvn"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41721

            Bug ID: 41721
           Summary: gvn produces wrong code with "opt -inline -mem2reg
                    -instcombine -licm -reg2mem -memcpyopt -gvn"
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: cszide at 163.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 21883
  --> https://bugs.llvm.org/attachment.cgi?id=21883&action=edit
.bc file of the source code

$clang -v
clang version 9.0.0 (trunk 355281)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/jack-zhou/Documents/llvm/llvm_truck/llvm/build4/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.5.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/8
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/7.3.0
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64

$clang -O3 -c -emit-llvm  -mllvm -disable-llvm-optzns small.c

$clang small.bc -o small1.out && ./small1.out
84957F6D

$opt -inline -mem2reg -instcombine -licm -reg2mem -memcpyopt -gvn   small.bc -o
small-opt.bc

$clang small-opt.bc -o small2.out && ./small2.out
0

without gvn, the result is correct.
$opt -inline -mem2reg -instcombine -licm -reg2mem -memcpyopt  small.bc -o
small-opt1.bc

$clang small-opt1.bc -o small3.out && ./small3.out
84957F6D

---------------------------------------------
#include<stdio.h>
typedef unsigned char           uint8_t;
typedef unsigned int            uint32_t;
typedef unsigned long int       uint64_t;

static uint32_t crc32_tab[256];
static uint32_t crc32_context = 0xFFFFFFFFUL;

static void crc32_gentab (void)
{
 uint32_t crc;
 const uint32_t poly = 0xEDB88320UL;
 int i, j;

 for (i = 0; i < 256; i++) {
  crc = i;
  for (j = 8; j > 0; j--) {
   if (crc & 1) {
    crc = (crc >> 1) ^ poly;
   } else {
    crc >>= 1;
   }
  }
  crc32_tab[i] = crc;
 }
}

static void crc32_byte (uint8_t b) {
 crc32_context =
  ((crc32_context >> 8) & 0x00FFFFFF) ^
  crc32_tab[(crc32_context ^ b) & 0xFF];
}

static void crc32_8bytes (uint64_t val)
{
 crc32_byte ((val>>0) & 0xff);
 crc32_byte ((val>>8) & 0xff);
 crc32_byte ((val>>16) & 0xff);
 crc32_byte ((val>>24) & 0xff);
 crc32_byte ((val>>32) & 0xff);
 crc32_byte ((val>>40) & 0xff);
 crc32_byte ((val>>48) & 0xff);
 crc32_byte ((val>>56) & 0xff);
}

static void transparent_crc (uint64_t val)
{
 crc32_8bytes(val);
}
int a=0, b=0, c=0;
void main() {
  crc32_gentab();
  for (; b < 9; b++) {
    c = 0;
    for (; c < 3; c++)
      transparent_crc(a);
  }
  printf("%lX\n",crc32_context ^ 0xFFFFFFFFUL);
}

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