LLVMとは？

様々なプログラミング言語に対し、様々なコンピュータやOSに対応させることができる共通基盤
中間言語に変換し、中間コードは、特定の機種やOSで直に動作するネイティブコードに変換して実行される
実行時に変換しながら実行するのは仮想マシン
RustやSwiftはLLVMの利用を前提としている

$ sudo apt install clang -y
$ clang -S -emit-llvm -O3 helloworld.c
$ cat helloworld.ll

; ModuleID = 'helloworld.c'
source_filename = "helloworld.c"
target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
target triple = "aarch64-unknown-linux-gnu"

@str = private unnamed_addr constant [14 x i8] c"Hello, world!\00", align 1

; Function Attrs: nofree nounwind uwtable
define dso_local i32 @main(i32 noundef %0, i8** nocapture noundef readnone %1) local_unnamed_addr #0 {
  %3 = tail call i32 @puts(i8* nonnull dereferenceable(1) getelementptr inbounds ([14 x i8], [14 x i8]* @str, i64 0, i64 0))
  ret i32 0
}

; Function Attrs: nofree nounwind
declare noundef i32 @puts(i8* nocapture noundef readonly) local_unnamed_addr #1

attributes #0 = { nofree nounwind uwtable "frame-pointer"="non-leaf" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="generic" "target-features"="+neon,+outline-atomics,+v8a" }
attributes #1 = { nofree nounwind }

!llvm.module.flags = !{!0, !1, !2, !3, !4, !5, !6, !7, !8}
!llvm.ident = !{!9}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 1, !"branch-target-enforcement", i32 0}
!2 = !{i32 1, !"sign-return-address", i32 0}
!3 = !{i32 1, !"sign-return-address-all", i32 0}
!4 = !{i32 1, !"sign-return-address-with-bkey", i32 0}
!5 = !{i32 7, !"PIC Level", i32 2}
!6 = !{i32 7, !"PIE Level", i32 2}
!7 = !{i32 7, !"uwtable", i32 1}
!8 = !{i32 7, !"frame-pointer", i32 1}
!9 = !{!"Ubuntu clang version 14.0.0-1ubuntu1.1"}