[PATCH 6/6] d3dx9_36/tests: fixed order of parameters

[Henri Verbeet]

On Wed, 29 Sept 2021 at 09:19, Eric Pouech <eric.pouech at gmail.com> wrote:
>
> to be complete:
> gcc11 complains with:
> In function 'unit_vec2',
>     inlined from 'attempt_line_merge' at /home/eric/work/wine/dlls/d3dx9_36/mesh.c:5542:5:
> /home/eric/work/wine/dlls/d3dx9_36/mesh.c:5511:12: warning: 'lastdir' may be used uninitialized [-Wmaybe-uninitialized]
>  5511 |     return D3DXVec2Normalize(D3DXVec2Subtract(dir, pt2, pt1), dir);
>       |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In file included from /home/eric/work/wine/include/d3dx9.h:31,
>                  from /home/eric/work/wine/dlls/d3dx9_36/d3dx9_private.h:32,
>                  from /home/eric/work/wine/dlls/d3dx9_36/mesh.c:31:
> /home/eric/work/wine/dlls/d3dx9_36/mesh.c: In function 'attempt_line_merge':
> /home/eric/work/wine/include/d3dx9math.h:352:21: note: by argument 2 of type 'const D3DXVECTOR2 *' to 'D3DXVec2Normalize' declared here
>   352 | D3DXVECTOR2* WINAPI D3DXVec2Normalize(D3DXVECTOR2 *pout, const D3DXVECTOR2 *pv);
>       |                     ^~~~~~~~~~~~~~~~~
> /home/eric/work/wine/dlls/d3dx9_36/mesh.c:5527:25: note: 'lastdir' declared here
>  5527 |     D3DXVECTOR2 curdir, lastdir;
>       |                         ^~~~~~~
>
> as D3DXV2Normalize isn't symetrical in its arguments definition (first arg is const ptr as input, while second arg is ptr as output)
> so gcc11 complains about passing as first arg (being a const ptr) an uninitialized object (it has no way of knowing that both args are aliased)
>
I don't think that's exactly what's happening. In particular, note
that the message complains about the second argument to
D3DXVec2Normalize(), not the first. My guess is that it doesn't notice
that the D3DXVec2Subtract() call initialises "dir" before the call to
D3DXVec2Normalize() actually happens. That's admittedly a little
tricky; the straightforward translation would first push "dir" to the
stack, which points to uninitialised memory at that point, then call
D3DXVec2Subtract() which initialises the vector pointed to by "dir",
push the return value of D3DXVec2Subtract(), and finally call
D3DXVec2Normalize().

In any case, I think the change makes things more readable, so in that
regard I think it's fine; I'd quibble a little about the commit
message. It's up to Matteo to sign off on this patch though.