change backend_init code to workaround bug in VC optimizer

[rainers]

The VC optimizer fails to change tysize[TYnref] when using optimized builds, all other entries seem ok.

This is clearly a MS compiler bug, but removing the non-looping loop seems to help avoid the troubles. Is there a reason to keep these loops running from 0 to 0?

I'm not sure why this worked before the frontend switch to D. Maybe the link time code generation uses a slightly different code generator.

I'm currently using VS2013 Update 4.

[rainers]

With this patch and #5010, I finally get a working (i.e. passing the test suite) release build using VC for the backend. Apart from better debugging, it generates faster code than dmc. Compile times for the D sources of ddmd with -m32 -O -inline using the respective dmd version:

• dmd2.067: 45.3 s
• dmd2.068.1: 46.3 s
• git-master: 47.8 s
• vc-win32: 38.3 s
• vc-x64: 37.9 s

Building the debug version takes about 2 seconds, so I expect the additional time is spent in the optimizer.

[WalterBright]

The strange loop is an anachronism from olden code.

[ibuclaw]

The strange loop is an anachronism from olden code.

Which I expect would have been better written as 'do { ... } while (0)' some years later. ;)