koch fails to boot nim with VCC compile backend

[fredrikhr]

When booting the nim compiler with the koch utility, by using koch boot -d:release to produces a release build, it critically fails in the 2^nd iteration.

msgs.nim(602, 32) Error: ambiguous call; both tables.[](t: var Table[[].A, [].B], key: A)[declared in lib\pure\collections\tables.nim(167, 5)] and tables.[](t: Table[[].A, [].B], key: A)[declared in lib\pure\collections\tables.nim(161, 5)] match for: (Table[system.string, system.int32], string)

According to @Araq, this is a regression caused by MSVC that miscompiles nim in the first iteration.

@Araq also stated on IRC that the issue is caused in compiler/semcall.nim (line 70) where MSVC appearently prematurely collects an important data structure in an attempt to optimize away the stack root.

This error does not occur when running koch boot which produces a non-optimized version of the compiler.

This currently makes it impossible to produce a release build of Nim with the VCC compiler backend.

[cooldome]

please specify VS version

[fredrikhr]

@cooldome VS2017

[barcharcraz]

I have had this issue as well.

setting vcc.exe to "clang-cl" (and having clang installed ofc) fixes it. So it may be an actual codegen regression and not a well-known bug in msvc

[fredrikhr]

This now works fine with booting Nim for x86 using koch boot -d:release --cpu:i386.

[fredrikhr]

I can however confirm that the same error still occurs when using vcc and booting nim for x64 with (as per the time of this comment) the newest commit on origin/devel

[nc-x]

It now builds fine with -d:release but not with -d:danger.