LLVM: lower optional types as byref=true

[andrewrk]

This is a possible workaround for
llvm/llvm-project#56585

On my computer it makes stage3-release go from false positive
compilation errors on the behavior tests to "segmentation fault".
Is this forwards progress or backwards progress? I have no idea.

See #11450

[andrewrk]

[nix-shell:~/dev/zig/build-release]$ hyperfine 'stage1/bin/zig build -Dskip-install-lib-files' 'stage2-release/bin/zig build -Dskip-install-lib-files' 'stage3-release/bin/zig build -Dskip-install-lib-files' 'stage3-bootstrap/bin/zig build -Dskip-install-lib-files' 'stage3-release-byref/bin/zig build -Dskip-install-lib-files' --warmup 2 -p 'rm -rf ../zig-cache ../zig-out'
Benchmark 1: stage1/bin/zig build -Dskip-install-lib-files
  Time (mean ± σ):     53.505 s ±  0.540 s    [User: 52.904 s, System: 2.726 s]
  Range (min … max):   52.793 s … 54.576 s    10 runs
 
Benchmark 2: stage2-release/bin/zig build -Dskip-install-lib-files
  Time (mean ± σ):     43.236 s ±  0.448 s    [User: 42.592 s, System: 1.041 s]
  Range (min … max):   42.667 s … 44.200 s    10 runs
 
Benchmark 3: stage3-release/bin/zig build -Dskip-install-lib-files
  Time (mean ± σ):     43.526 s ±  0.683 s    [User: 42.918 s, System: 1.028 s]
  Range (min … max):   42.826 s … 45.384 s    10 runs
 
  Warning: Statistical outliers were detected. Consider re-running this benchmark on a quiet PC without any interferences from other programs. It might help to use the '--warmup' or '--prepare' options.
 
Benchmark 4: stage3-bootstrap/bin/zig build -Dskip-install-lib-files
  Time (mean ± σ):     45.934 s ±  0.717 s    [User: 43.644 s, System: 2.686 s]
  Range (min … max):   45.212 s … 47.513 s    10 runs
 
Benchmark 5: stage3-release-byref/bin/zig build -Dskip-install-lib-files
  Time (mean ± σ):     35.169 s ±  0.346 s    [User: 34.548 s, System: 1.045 s]
  Range (min … max):   34.793 s … 35.919 s    10 runs
 
Summary
  'stage3-release-byref/bin/zig build -Dskip-install-lib-files' ran
    1.23 ± 0.02 times faster than 'stage2-release/bin/zig build -Dskip-install-lib-files'
    1.24 ± 0.02 times faster than 'stage3-release/bin/zig build -Dskip-install-lib-files'
    1.31 ± 0.02 times faster than 'stage3-bootstrap/bin/zig build -Dskip-install-lib-files'
    1.52 ± 0.02 times faster than 'stage1/bin/zig build -Dskip-install-lib-files'

stage3-release-byref is this branch + #12145

[andrewrk]

This branch originally started out as a potential workaround to address #11450. It did not solve that problem, however, it did end up fixing #11498!

[erikarvstedt]

Did this solve a cause of bloat that was unique to stage 2?
Or one that was common to both stage 1 and 2, so that more potential for de-bloating stage 2 binaries remains?

[andrewrk]

Did this solve a cause of bloat that was unique to stage 2?

• stage2-generated binaries are slower and more bloated than stage1-generated binaries #11498