[PATCH] D54604: Automatic variable initialization

[Alexander Potapenko via Phabricator via cfe-commits]

glider added a comment.

Not sure if a similar problem was mentioned already or not, but the following program:

  void alloc_sock(int *err);
  int try_send();
  
  int send(int len) {
    int err;
    if (len) {
      err = -1; 
      alloc_sock(&err);
      err = try_send();
    }
    return -1; 
  }

produces a redundant store of `0xaaaaaaaa` to `err`:

  0000000000000000 <send>:
  void alloc_sock(int *err);
  int try_send();
  
  int send(int len) {
     0:   50                      push   %rax
    int err;
     1:   c7 44 24 04 aa aa aa    movl   $0xaaaaaaaa,0x4(%rsp)
     8:   aa 
    if (len) {
     9:   85 ff                   test   %edi,%edi
     b:   74 1d                   je     2a <send+0x2a>
      err = -1;
     d:   c7 44 24 04 ff ff ff    movl   $0xffffffff,0x4(%rsp)
    14:   ff 
    15:   48 8d 7c 24 04          lea    0x4(%rsp),%rdi
      alloc_sock(&err);
    1a:   e8 00 00 00 00          callq  1f <send+0x1f>
                          1b: R_X86_64_PLT32      alloc_sock-0x4
      err = try_send();
    1f:   31 c0                   xor    %eax,%eax
    21:   e8 00 00 00 00          callq  26 <send+0x26>
                          22: R_X86_64_PLT32      try_send-0x4
    26:   89 44 24 04             mov    %eax,0x4(%rsp)
    }
    return -1;
    2a:   b8 ff ff ff ff          mov    $0xffffffff,%eax
    2f:   59                      pop    %rcx
    30:   c3                      retq  

Not sure whether this isn't a bug in DSE though.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D54604/new/

https://reviews.llvm.org/D54604