VC++ 6.0 epic failure on some cube2 code

by lordofspace on 08/08/2009 08:56, 0 messages, last message: 08/08/2009 08:56, 938 views, last view: 04/25/2024 00:30

This doesn't have much to do with Sauerbraten per se, but rather with some of its code. The code is in tools.h, which I have used in one of my own projects. I recently had the misfortune of migrating my project into Visual C++ 6.0 for a friend of mine and ran across this gem in the custom vector class:

void drop() { buf[--ulen].~T(); }

which setsize(int) compiles to ->

mov eax, [ecx+8]
mov ecx, [esp+arg_0]
cmp eax, ecx
jle short locret_1000839D
loc_1000839B:
jmp short loc_1000839B
locret_1000839D:
retn 4

For the assembler uninclined, allow me translate back into c++ (note call to destructor was not present as this was for a type with trivial destructor):

void setsize(int x)
{
if(ulen <= x)
return;
while(1){}
}

Clearly not even close to correct!
If we change drop() to the following, everything is peachy keen:

void drop() { ulen--; buf[ulen].~T(); }

The asm generated in this case behaves exactly as expected.
Just thought I'd share this somewhat irrelevant but silly behavior of an ancient, but still used compiler.

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