[llvm-bugs] [Bug 42043] New: loop-reroll produces wrong code with "opt -jump-threading -prune-eh -loop-extract-single -prune-eh -instcombine -loop-rotate -inline -licm -loop-unroll -forceattrs -gvn -loop-reroll"

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42043

            Bug ID: 42043
           Summary: loop-reroll produces wrong code with "opt
                    -jump-threading -prune-eh -loop-extract-single
                    -prune-eh -instcombine -loop-rotate -inline -licm
                    -loop-unroll -forceattrs -gvn -loop-reroll"
           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 22026
  --> https://bugs.llvm.org/attachment.cgi?id=22026&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

$gcc small.c -o small0.out && ./small0.out
9

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

$clang small.bc -o small1.out && ./small1.out 
9

$opt -jump-threading -prune-eh -loop-extract-single -prune-eh -instcombine
-loop-rotate -inline -licm -loop-unroll -forceattrs -gvn -loop-reroll small.bc
-o small-opt.bc

$clang small-opt.bc -o small2.out && ./small2.out 
54

without loop-reroll pass, the output is correct.
$opt -jump-threading -prune-eh -loop-extract-single -prune-eh -instcombine
-loop-rotate -inline -licm -loop-unroll -forceattrs -gvn  small.bc -o
small-opt1.bc

$clang small-opt1.bc -o small3.out && ./small3.out
9

------------------------------------------------
#include <stdio.h>
int a=0, b=0;
void c() {
  unsigned short int d[9][6];
  int e=0;
  for (e = 0; e;)
    ;
  for (a=0; a < 9; a++)
    for (b = 0; b < 6; b++)
      d[a][b] = 2;
}
void main() {
  c();
  printf("%d\n",a);
}

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