fix TLS alignment for Windows 8.0 or below

[rainers]

Even though documented in MSDN for VS2003 (https://msdn.microsoft.com/de-de/library/83ythb65%28v=vs.71%29.aspx), TLS alignment seems not to be implemented before Windows 8.1.

Both the align() attibute aswell as LLVM optimizations require alignments higher than the default, so to not exclude Windows 7 users from using executables built with LDC, this allocates another TLS segment aligned appropraitely and replaces the one allocated by the OS.

[kinke]

Thanks, looks good! Just needs some clang-format love to keep things consistent. I'll hopefully be able to test it tomorrow on my Win7 box at work.

[rainers]

I amended a little cleanup, adding spaces for cast expressions. I guess the 5/3 indentation in the for loop isn't supposed to be followed.

I've tried a prototype of this on a fresh install of Win7 in a VM (dating back to 2009) and with an up-to-date Win7.

[kinke]

Very good. So you're not using the clang-format VS plugin (here, at the bottom)? I just press Ctrl+A to select the whole file and then select Tools -> ClangFormat, no need for any config. I can do it for you if you don't want to install it.

[rainers]

So you're not using the clang-format VS plugin

I use it for LDC code, but druntime code has very different coding style.

[kinke]

Oh I forgot that we're in druntime here for a second. Okay then I refrain from being that nitpicky. ;)

[kinke]

int alignmentMask = (1 << (alignShift - 1)) - 1;?

[JohanEngelen]

Could this be a reason why LDC master built with LDC0.17 does not work on Windows?

[kinke]

I don't think so. As the front-end comes from C++, I don't think it uses a lot of TLS stuff. And the default 16-bytes alignment for Win64 should be enough. I haven't experienced any non-synthetic TLS alignment problems on Win64 at all yet; this only came up on Win32 with its 8-bytes alignment.
Without having looked at the errors yet, I'd guess the problem stems from 64-bit reals when compiling the front-end with LDC.

[rainers]

alignmentMask

Ok, updated.

[kinke]

I've cherry-picked your first commit for origin's msvcEH branch (#65) and amended the alignmentMask thingy myself to keep the diff as small as possible (no line ending changes). It will be tested by the next AppVeyor round for ldc-developers/ldc#1354 (the AppVeyor images use at least Win 8.1 - but I trust your tests).
Thanks for the thorough investigation (.CRT$XLB), excellent work!

[rainers]

(no line ending changes)

Ouch, sorry for that. This creeps in from time to time, even with the .editorConfig plugin. I suspect it's my diff tool that is to blame (beyond compare).

[rainers]

Now part of dlang#1354, can close this PR.