Created attachment 25252 [details]
xz-compressed bitcode input file

I'm seeing a codegen slowdown by about 2 orders of magnitude for the attached .bc file (generated by LDC, the LLVM D compiler) starting with LLVM 12.0.0. Seems to be specific to Windows/MSVC targets, and timings are back to normal when enabling the optimizer.

Using clang from the official LLVM Windows builds from GitHub and compiling via `clang -c template9.bc`:
* v11.0.1: ~2.4 seconds
* v12.0.1: ~246 seconds
* v13.0.0-rc2: ~227 seconds

Enabling the optimizer by adding `-O3` hints at a further little regression in v13:
* v11.0.1: ~3.3 seconds
* v12.0.1: ~3.3 seconds
* v13.0.0-rc2: ~5.0 seconds