Broken variable length array

[Codetector1374]

__attribute__((noinline))
int simple(unsigned n) {
  volatile int shit[n];
  volatile int a;
  shit[n-1] = n;
  return a;
}

; ModuleID = 'simple.c'
source_filename = "simple.c"
target datalayout = "E-m:e-S32-p:32:32:32-i32:32:32-a:32:32-n32"
target triple = "tl45-unknown-unknown-elf"

; Function Attrs: noinline nounwind
define dso_local i32 @simple(i32 %n) local_unnamed_addr #0 {
entry:
  %a = alloca i32, align 4
  %vla = alloca i32, i32 %n, align 4
  %a.0.a.0..sroa_cast = bitcast i32* %a to i8*
  call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %a.0.a.0..sroa_cast)
  %sub = add i32 %n, -1
  %arrayidx = getelementptr inbounds i32, i32* %vla, i32 %sub
  store volatile i32 %n, i32* %arrayidx, align 4, !tbaa !2
  %a.0.a.0. = load volatile i32, i32* %a, align 4, !tbaa !2
  call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %a.0.a.0..sroa_cast)
  ret i32 %a.0.a.0.
}
; Function Attrs: argmemonly nounwind willreturn
declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #1

; Function Attrs: argmemonly nounwind willreturn
declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #1

attributes #0 = { noinline nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { argmemonly nounwind willreturn }
attributes #2 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="none" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.module.flags = !{!0}
!llvm.ident = !{!1}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{!"clang version 10.0.0 ([email protected]:transfer-learning/llvm-tl45.git 9c609f55e093b10737f8006ade652e06a6a1d976)"}
!2 = !{!3, !3, i64 0}
!3 = !{!"int", !4, i64 0}
!4 = !{!"omnipotent char", !5, i64 0}
!5 = !{!"Simple C/C++ TBAA"}