After wrangling with some missing compiler intrinsics, I've been able to get CPython to build with an almost vanilla clang-cl!

I plan on upstreaming the patches to the LLVM project once I clean them up a bit. After that I will clean up the CPython patches and send a PR.

I also ran performance with master built on MSVC compared to my branch on clang-cl with computed-goto enabled (I wasn't sure if there are other things that may be possible to turn on, computed goto seemed an obvious win). The results are decent, but some things, like json loads, are much slower (not sure why that is). The full report:


msvc.json
=========

Performance version: 0.6.1
Report on Windows-10-10.0.17672-SP0
Number of logical CPUs: 12
Start date: 2018-05-24 03:40:09.082701
End date: 2018-05-24 04:08:57.993717

clang2goto.json
===============

Performance version: 0.6.1
Report on Windows-10-10.0.17672-SP0
Number of logical CPUs: 12
Start date: 2018-05-24 04:29:01.214005
End date: 2018-05-24 04:57:08.774299

### 2to3 ###
Mean +- std dev: 675 ms +- 31 ms -> 655 ms +- 32 ms: 1.03x faster
Significant (t=3.55)

### chameleon ###
Mean +- std dev: 19.5 ms +- 0.5 ms -> 18.1 ms +- 0.7 ms: 1.08x faster
Significant (t=13.19)

### chaos ###
Mean +- std dev: 230 ms +- 6 ms -> 209 ms +- 8 ms: 1.10x faster
Significant (t=16.39)

### crypto_pyaes ###
Mean +- std dev: 212 ms +- 8 ms -> 197 ms +- 8 ms: 1.07x faster
Significant (t=9.72)

### deltablue ###
Mean +- std dev: 15.2 ms +- 0.6 ms -> 14.2 ms +- 0.5 ms: 1.07x faster
Significant (t=10.23)

### django_template ###
Mean +- std dev: 222 ms +- 9 ms -> 210 ms +- 8 ms: 1.06x faster
Significant (t=8.10)

### dulwich_log ###
Mean +- std dev: 235 ms +- 13 ms -> 230 ms +- 12 ms: 1.02x faster
Significant (t=2.18)

### fannkuch ###
Mean +- std dev: 905 ms +- 11 ms -> 802 ms +- 15 ms: 1.13x faster
Significant (t=42.95)

### float ###
Mean +- std dev: 226 ms +- 9 ms -> 197 ms +- 8 ms: 1.15x faster
Significant (t=18.71)

### go ###
Mean +- std dev: 485 ms +- 10 ms -> 445 ms +- 8 ms: 1.09x faster
Significant (t=24.60)

### hexiom ###
Mean +- std dev: 19.9 ms +- 0.9 ms -> 18.3 ms +- 0.8 ms: 1.08x faster
Significant (t=9.51)

### html5lib ###
Mean +- std dev: 156 ms +- 9 ms -> 149 ms +- 9 ms: 1.05x faster
Significant (t=4.31)

### json_dumps ###
Mean +- std dev: 23.4 ms +- 1.2 ms -> 23.0 ms +- 1.1 ms: 1.02x faster
Not significant

### json_loads ###
Mean +- std dev: 49.3 us +- 2.2 us -> 93.2 us +- 8.7 us: 1.89x slower
Significant (t=-37.79)

### logging_format ###
Mean +- std dev: 25.3 us +- 1.3 us -> 23.4 us +- 1.2 us: 1.08x faster
Significant (t=8.48)

### logging_silent ###
Mean +- std dev: 368 ns +- 14 ns -> 340 ns +- 21 ns: 1.08x faster
Significant (t=8.69)

### logging_simple ###
Mean +- std dev: 23.1 us +- 1.4 us -> 20.6 us +- 0.9 us: 1.12x faster
Significant (t=11.66)

### mako ###
Mean +- std dev: 36.7 ms +- 1.8 ms -> 36.0 ms +- 1.7 ms: 1.02x faster
Not significant

### meteor_contest ###
Mean +- std dev: 189 ms +- 9 ms -> 175 ms +- 9 ms: 1.08x faster
Significant (t=9.09)

### nbody ###
Mean +- std dev: 274 ms +- 12 ms -> 222 ms +- 8 ms: 1.24x faster
Significant (t=28.22)

### nqueens ###
Mean +- std dev: 198 ms +- 8 ms -> 174 ms +- 8 ms: 1.14x faster
Significant (t=16.67)

### pathlib ###
Mean +- std dev: 343 ms +- 19 ms -> 338 ms +- 18 ms: 1.02x faster
Not significant

### pickle ###
Mean +- std dev: 20.9 us +- 0.8 us -> 19.9 us +- 0.5 us: 1.05x faster
Significant (t=8.91)

### pickle_dict ###
Mean +- std dev: 50.0 us +- 1.9 us -> 51.2 us +- 3.0 us: 1.02x slower
Significant (t=-2.62)

### pickle_list ###
Mean +- std dev: 7.61 us +- 0.32 us -> 7.06 us +- 0.36 us: 1.08x faster
Significant (t=8.92)

### pickle_pure_python ###
Mean +- std dev: 964 us +- 52 us -> 879 us +- 43 us: 1.10x faster
Significant (t=9.72)

### pidigits ###
Mean +- std dev: 257 ms +- 5 ms -> 254 ms +- 9 ms: 1.01x faster
Not significant

### python_startup ###
Mean +- std dev: 69.6 ms +- 8.3 ms -> 69.5 ms +- 6.3 ms: 1.00x faster
Not significant

### python_startup_no_site ###
Mean +- std dev: 57.7 ms +- 6.6 ms -> 58.2 ms +- 6.0 ms: 1.01x slower
Not significant

### raytrace ###
Mean +- std dev: 1.00 sec +- 0.02 sec -> 0.94 sec +- 0.02 sec: 1.07x faster
Significant (t=21.49)

### regex_compile ###
Mean +- std dev: 335 ms +- 5 ms -> 306 ms +- 10 ms: 1.10x faster
Significant (t=20.75)

### regex_dna ###
Mean +- std dev: 237 ms +- 7 ms -> 266 ms +- 7 ms: 1.13x slower
Significant (t=-23.71)

### regex_effbot ###
Mean +- std dev: 4.42 ms +- 0.17 ms -> 4.82 ms +- 0.20 ms: 1.09x slower
Significant (t=-12.07)

### regex_v8 ###
Mean +- std dev: 45.2 ms +- 15.5 ms -> 39.7 ms +- 2.8 ms: 1.14x faster
Significant (t=2.74)

### richards ###
Mean +- std dev: 152 ms +- 8 ms -> 142 ms +- 9 ms: 1.07x faster
Significant (t=6.19)

### scimark_fft ###
Mean +- std dev: 665 ms +- 12 ms -> 593 ms +- 12 ms: 1.12x faster
Significant (t=32.36)

### scimark_lu ###
Mean +- std dev: 327 ms +- 11 ms -> 324 ms +- 11 ms: 1.01x faster
Not significant

### scimark_monte_carlo ###
Mean +- std dev: 205 ms +- 7 ms -> 192 ms +- 8 ms: 1.07x faster
Significant (t=9.22)

### scimark_sor ###
Mean +- std dev: 386 ms +- 11 ms -> 351 ms +- 11 ms: 1.10x faster
Significant (t=18.36)

### scimark_sparse_mat_mult ###
Mean +- std dev: 8.39 ms +- 0.31 ms -> 7.19 ms +- 0.40 ms: 1.17x faster
Significant (t=18.44)

### spectral_norm ###
Mean +- std dev: 279 ms +- 8 ms -> 238 ms +- 7 ms: 1.17x faster
Significant (t=29.08)

### sqlalchemy_declarative ###
Mean +- std dev: 250 ms +- 12 ms -> 245 ms +- 10 ms: 1.02x faster
Significant (t=2.73)

### sqlalchemy_imperative ###
Mean +- std dev: 47.2 ms +- 2.4 ms -> 47.4 ms +- 2.5 ms: 1.00x slower
Not significant

### sqlite_synth ###
Mean +- std dev: 5.37 us +- 0.25 us -> 5.22 us +- 0.21 us: 1.03x faster
Significant (t=3.60)

### sympy_expand ###
Mean +- std dev: 710 ms +- 16 ms -> 671 ms +- 20 ms: 1.06x faster
Significant (t=11.92)

### sympy_integrate ###
Mean +- std dev: 31.9 ms +- 1.3 ms -> 30.5 ms +- 1.4 ms: 1.05x faster
Significant (t=5.51)

### sympy_str ###
Mean +- std dev: 313 ms +- 9 ms -> 297 ms +- 8 ms: 1.05x faster
Significant (t=10.39)

### sympy_sum ###
Mean +- std dev: 151 ms +- 6 ms -> 143 ms +- 6 ms: 1.05x faster
Significant (t=6.70)

### telco ###
Mean +- std dev: 11.2 ms +- 0.4 ms -> 10.8 ms +- 0.4 ms: 1.04x faster
Significant (t=5.45)

### unpack_sequence ###
Mean +- std dev: 87.1 ns +- 3.8 ns -> 67.3 ns +- 4.3 ns: 1.29x faster
Significant (t=26.90)

### unpickle ###
Mean +- std dev: 27.4 us +- 1.9 us -> 25.3 us +- 1.5 us: 1.08x faster
Significant (t=6.46)

### unpickle_list ###
Mean +- std dev: 6.81 us +- 0.29 us -> 6.15 us +- 0.30 us: 1.11x faster
Significant (t=12.38)

### unpickle_pure_python ###
Mean +- std dev: 740 us +- 31 us -> 696 us +- 38 us: 1.06x faster
Significant (t=6.82)

### xml_etree_generate ###
Mean +- std dev: 197 ms +- 13 ms -> 190 ms +- 11 ms: 1.04x faster
Significant (t=3.34)

### xml_etree_iterparse ###
Mean +- std dev: 177 ms +- 12 ms -> 174 ms +- 11 ms: 1.02x faster
Not significant

### xml_etree_parse ###
Mean +- std dev: 229 ms +- 13 ms -> 229 ms +- 13 ms: 1.00x faster
Not significant

### xml_etree_process ###
Mean +- std dev: 161 ms +- 11 ms -> 154 ms +- 10 ms: 1.04x faster
Significant (t=3.45)