g++ is being gay


Data BSTree::retrieve(const KeyType& key, BSTree::Node *cur) const
{
    if(!cur)
        return Data();
    else if(key == cur->data.key)
        return cur->data;
    cur = key > cur->data.key ? cur->right : cur->left;
    return retrieve(key, cur);
}

This is a tail-call, yes? But when I compile with "g++ -S BSTree.cpp -Wall -pedantic -O2 -foptimize-sibling-calls", I get this assembly code.


_ZNK6BSTree8retrieveERKjPNS_4NodeE:
.LFB791:
    testq    %rcx, %rcx
    pushq    %rbx
.LCFI0:
    movq    %rdi, %rbx
    je    .L13
    movl    (%rdx), %eax
    cmpl    (%rcx), %eax
    je    .L14
    ja    .L15
    movq    16(%rcx), %rcx
.L10:
    movq    %rbx, %rdi
        ; LOL WTF IS THIS SHIT
    call    _ZNK6BSTree8retrieveERKjPNS_4NodeE
    movq    %rbx, %rax
    popq    %rbx
    .p2align 4,,1
    .p2align 3
    ret
    .p2align 4,,10
    .p2align 3
.L15:
    movq    24(%rcx), %rcx
    jmp    .L10
    .p2align 4,,10
    .p2align 3
.L13:
    movq    %rbx, %rax
    movl    $0, (%rdi)
    movq    $_ZNSs4_Rep20_S_empty_rep_storageE+24, 8(%rdi)
    popq    %rbx
    ret
    .p2align 4,,10
    .p2align 3
.L14:
    movl    %eax, (%rdi)
    leaq    8(%rcx), %rsi
    leaq    8(%rdi), %rdi
    call    _ZNSsC1ERKSs
    movq    %rbx, %rax
    popq    %rbx
    ret

I'm about to give up and just put in a fucking goto.

>>13
Semantics = meaning.
Tail-call optimization changes the meaning of the original code, even though the output will still be the same. Kind of like how using bubble sort and quick sort will still sort a list, but the way they do it is different.