[Issue 14436] Optimizer fails to remove comparison loop when comparing array against null

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14436

Marc Schütz <schuetzm at gmx.net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |REOPENED
                 CC|                            |schuetzm at gmx.net
         Resolution|FIXED                       |---

--- Comment #3 from Marc Schütz <schuetzm at gmx.net> ---
Comparing with an empty array or string literal still generates suboptimal
code:

bool isEmpty(string s) {
        return s == "";
}

# dmd -c -O -inline -release xx.d

0000000000000000 <_D2xx7isEmptyFAyaZb>:
   0:    55                       push   %rbp
   1:    48 8b ec                 mov    %rsp,%rbp
   4:    48 83 ec 10              sub    $0x10,%rsp
   8:    48 89 7d f0              mov    %rdi,-0x10(%rbp)
   c:    48 89 75 f8              mov    %rsi,-0x8(%rbp)
  10:    48 3b 3d 00 00 00 00     cmp    0x0(%rip),%rdi        # 17
<_D2xx7isEmptyFAyaZb+0x17>
  17:    75 15                    jne    2e <_D2xx7isEmptyFAyaZb+0x2e>
  19:    48 8b 75 f8              mov    -0x8(%rbp),%rsi
  1d:    48 8b 3d 00 00 00 00     mov    0x0(%rip),%rdi        # 24
<_D2xx7isEmptyFAyaZb+0x24>
  24:    48 8b 4d f0              mov    -0x10(%rbp),%rcx
  28:    33 c0                    xor    %eax,%eax
  2a:    f3 a6                    repz cmpsb %es:(%rdi),%ds:(%rsi)
  2c:    74 04                    je     32 <_D2xx7isEmptyFAyaZb+0x32>
  2e:    31 c0                    xor    %eax,%eax
  30:    eb 05                    jmp    37 <_D2xx7isEmptyFAyaZb+0x37>
  32:    b8 01 00 00 00           mov    $0x1,%eax
  37:    48 8b e5                 mov    %rbp,%rsp
  3a:    5d                       pop    %rbp
  3b:    c3                       retq   

Reopening, as it is a closely related enhancement (though strictly speaking not
identical).

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