; LLVM IR from ritikbanger/Hacktoberfest2022-DSA :: 10. Linked List/c lang/SinglyLinkedList (Reverse a Linked List)

; Unoptimized IR (clang -disable-llvm-passes):
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

%struct.node = type { i32, ptr }

@head = external dso_local global ptr, align 8

; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
declare void @llvm.lifetime.start.p0(i64 immarg, ptr nocapture) #0

; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
declare void @llvm.lifetime.end.p0(i64 immarg, ptr nocapture) #0

; Function Attrs: nounwind uwtable
define dso_local void @reverse() #1 {
  %1 = alloca ptr, align 8
  %2 = alloca ptr, align 8
  %3 = alloca ptr, align 8
  call void @llvm.lifetime.start.p0(i64 8, ptr %1) #2
  call void @llvm.lifetime.start.p0(i64 8, ptr %2) #2
  call void @llvm.lifetime.start.p0(i64 8, ptr %3) #2
  %4 = load ptr, ptr @head, align 8, !tbaa !5
  store ptr %4, ptr %1, align 8, !tbaa !5
  store ptr null, ptr %2, align 8, !tbaa !5
  br label %5

5:                                                ; preds = %8, %0
  %6 = load ptr, ptr %1, align 8, !tbaa !5
  %7 = icmp ne ptr %6, null
  br i1 %7, label %8, label %17

8:                                                ; preds = %5
  %9 = load ptr, ptr %1, align 8, !tbaa !5
  %10 = getelementptr inbounds %struct.node, ptr %9, i32 0, i32 1
  %11 = load ptr, ptr %10, align 8, !tbaa !9
  store ptr %11, ptr %3, align 8, !tbaa !5
  %12 = load ptr, ptr %2, align 8, !tbaa !5
  %13 = load ptr, ptr %1, align 8, !tbaa !5
  %14 = getelementptr inbounds %struct.node, ptr %13, i32 0, i32 1
  store ptr %12, ptr %14, align 8, !tbaa !9
  %15 = load ptr, ptr %1, align 8, !tbaa !5
  store ptr %15, ptr %2, align 8, !tbaa !5
  %16 = load ptr, ptr %3, align 8, !tbaa !5
  store ptr %16, ptr %1, align 8, !tbaa !5
  br label %5, !llvm.loop !12

17:                                               ; preds = %5
  %18 = load ptr, ptr %2, align 8, !tbaa !5
  store ptr %18, ptr @head, align 8, !tbaa !5
  call void @llvm.lifetime.end.p0(i64 8, ptr %3) #2
  call void @llvm.lifetime.end.p0(i64 8, ptr %2) #2
  call void @llvm.lifetime.end.p0(i64 8, ptr %1) #2
  ret void
}

attributes #0 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
attributes #1 = { nounwind uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
attributes #2 = { nounwind }

!llvm.module.flags = !{!0, !1, !2, !3}
!llvm.ident = !{!4}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 8, !"PIC Level", i32 2}
!2 = !{i32 7, !"PIE Level", i32 2}
!3 = !{i32 7, !"uwtable", i32 2}
!4 = !{!"clang version 19.1.0 (git@github.com:llvm/llvm-project.git a4bf6cd7cfb1a1421ba92bca9d017b49936c55e4)"}
!5 = !{!6, !6, i64 0}
!6 = !{!"any pointer", !7, i64 0}
!7 = !{!"omnipotent char", !8, i64 0}
!8 = !{!"Simple C/C++ TBAA"}
!9 = !{!10, !6, i64 8}
!10 = !{!"node", !11, i64 0, !6, i64 8}
!11 = !{!"int", !7, i64 0}
!12 = distinct !{!12, !13}
!13 = !{!"llvm.loop.mustprogress"}


; Optimized IR (opt -passes='default<O3>'):
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

@head = external dso_local local_unnamed_addr global ptr, align 8

; Function Attrs: nofree norecurse nosync nounwind memory(readwrite, inaccessiblemem: none) uwtable
define dso_local void @reverse() local_unnamed_addr #0 {
  %1 = load ptr, ptr @head, align 8, !tbaa !5
  %.not8 = icmp eq ptr %1, null
  br i1 %.not8, label %._crit_edge, label %.lr.ph

.lr.ph:                                           ; preds = %0, %.lr.ph
  %.010 = phi ptr [ %3, %.lr.ph ], [ %1, %0 ]
  %.079 = phi ptr [ %.010, %.lr.ph ], [ null, %0 ]
  %2 = getelementptr inbounds i8, ptr %.010, i64 8
  %3 = load ptr, ptr %2, align 8, !tbaa !9
  store ptr %.079, ptr %2, align 8, !tbaa !9
  %.not = icmp eq ptr %3, null
  br i1 %.not, label %._crit_edge, label %.lr.ph, !llvm.loop !12

._crit_edge:                                      ; preds = %.lr.ph, %0
  %.07.lcssa = phi ptr [ null, %0 ], [ %.010, %.lr.ph ]
  store ptr %.07.lcssa, ptr @head, align 8, !tbaa !5
  ret void
}

attributes #0 = { nofree norecurse nosync nounwind memory(readwrite, inaccessiblemem: none) uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }

!llvm.module.flags = !{!0, !1, !2, !3}
!llvm.ident = !{!4}

!0 = !{i32 1, !"wchar_size", i32 4}
!1 = !{i32 8, !"PIC Level", i32 2}
!2 = !{i32 7, !"PIE Level", i32 2}
!3 = !{i32 7, !"uwtable", i32 2}
!4 = !{!"clang version 19.1.0 (git@github.com:llvm/llvm-project.git a4bf6cd7cfb1a1421ba92bca9d017b49936c55e4)"}
!5 = !{!6, !6, i64 0}
!6 = !{!"any pointer", !7, i64 0}
!7 = !{!"omnipotent char", !8, i64 0}
!8 = !{!"Simple C/C++ TBAA"}
!9 = !{!10, !6, i64 8}
!10 = !{!"node", !11, i64 0, !6, i64 8}
!11 = !{!"int", !7, i64 0}
!12 = distinct !{!12, !13}
!13 = !{!"llvm.loop.mustprogress"}


; Effective O3 passes: EarlyCSEPass,GVNPass,GlobalOptPass,InferFunctionAttrsPass,InstCombinePass,InstSimplifyPass,JumpThreadingPass,LCSSAPass,LoopRotatePass,LoopSimplifyPass,LoopUnrollPass,PostOrderFunctionAttrsPass,SROAPass,SimplifyCFGPass