[llvm-dev] unusual use of getenv

[Luke Drummond via llvm-dev]

Hi Michael

On Tue Nov 10, 2020 at 1:29 AM GMT, Michael Kruse wrote:

> Am Mo., 2. Nov. 2020 um 14:01 Uhr schrieb David Blaikie
> <dblaikie at gmail.com>:
> > Hmm, not sure why the whole file was added only when MSVC support was added - if it is a "static library object file selection" issue. Wouldn't that have turned up on other platforms before that moment?
>
> It did turn up on non-Windows platforms in
> https://reviews.llvm.org/D61446. The name of the file where this trick
> is used "LinkAllPasses.h" should give a hint what it is used for.
> Looking into the entire history of the file, I have no idea how one
> would have concluded this whas a Windows thing. It first occurred in
> 1c5b428ff8234cef705bf57bc1418deb4db25c83 (SVN r23921) when Windows
> support was not yet a thing.

I concluded this was a windows thing because the origin of the code
seems to be in 00d5508496c1ec0540da5714b0ed66e64b623df5 which uses the
windows only `GetCurrentProcess` instead of `getenv`. Chris Lattner then
changed it to use `getenv` in 63e504ff437d88f0d4bdb0cd50b045655dea6ab1
(svn r23915).
00d550849 is svn r19307 and predates 1c5b428ff823 by ~9 months. The
"new header" patch you identified as the origin of this code seems to be a copy
of the original. Reid Spencer then consolidated the two in the subsequent patch
a3223665010b9a.

That's as far as my archaeology went on this. It's possible that
00d550849 includes code copied from elsewhere, but to me it looks like
00d550849 is the canonical origin of this code.

All the Best

Luke


-- 
Codeplay Software Ltd.
Company registered in England and Wales, number: 04567874
Registered office: Regent House, 316 Beulah Hill, London, SE19 3HF