Quoting edges names, as dot does not like names with dots. Fixing problem with "ret void" displaying. Switched to nicer rectangular shapes.

Tried graph-llvm-ir on the llvm code below and fixed several minor issues encountered.

$ cat example.ll
; ModuleID = '/home/marcusmae/Documents/llvm-graphs/example/example.c'
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define void @vector_sum(i32 %length, float* nocapture %in1, float* nocapture %in2, float* nocapture %out) nounwind uwtable {
entry:
  %cmp9 = icmp sgt i32 %length, 0
  br i1 %cmp9, label %for.body, label %for.end

for.body:                                         ; preds = %entry, %for.body
  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %entry ]
  %arrayidx = getelementptr inbounds float* %in1, i64 %indvars.iv
  %0 = load float* %arrayidx, align 4, !tbaa !0
  %arrayidx2 = getelementptr inbounds float* %in2, i64 %indvars.iv
  %1 = load float* %arrayidx2, align 4, !tbaa !0
  %add = fadd float %0, %1
  %arrayidx4 = getelementptr inbounds float* %out, i64 %indvars.iv
  store float %add, float* %arrayidx4, align 4, !tbaa !0
  %indvars.iv.next = add i64 %indvars.iv, 1
  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
  %exitcond = icmp eq i32 %lftr.wideiv, %length
  br i1 %exitcond, label %for.end, label %for.body

for.end:                                          ; preds = %for.body, %entry
  ret void
}

define i32 @main(i32 %argc, i8** nocapture %argv) nounwind uwtable {
entry:
  %cmp = icmp eq i32 %argc, 2
  br i1 %cmp, label %if.end, label %return

if.end:                                           ; preds = %entry
  %arrayidx = getelementptr inbounds i8** %argv, i64 1
  %0 = load i8** %arrayidx, align 8, !tbaa !3
  %call = tail call i32 @atoi(i8* %0) nounwind readonly
  %conv = sext i32 %call to i64
  %mul = shl nsw i64 %conv, 2
  %call1 = tail call noalias i8* @malloc(i64 %mul) nounwind
  %1 = bitcast i8* %call1 to float*
  %call4 = tail call noalias i8* @malloc(i64 %mul) nounwind
  %2 = bitcast i8* %call4 to float*
  %call7 = tail call noalias i8* @malloc(i64 %mul) nounwind
  %3 = bitcast i8* %call7 to float*
  %cmp826 = icmp sgt i32 %call, 0
  br i1 %cmp826, label %for.body, label %for.end

for.body:                                         ; preds = %if.end, %for.body
  %indvars.iv = phi i64 [ %indvars.iv.next, %for.body ], [ 0, %if.end ]
  %call10 = tail call double @drand48() nounwind
  %conv11 = fptrunc double %call10 to float
  %arrayidx12 = getelementptr inbounds float* %1, i64 %indvars.iv
  store float %conv11, float* %arrayidx12, align 4, !tbaa !0
  %call13 = tail call double @drand48() nounwind
  %conv14 = fptrunc double %call13 to float
  %arrayidx16 = getelementptr inbounds float* %2, i64 %indvars.iv
  store float %conv14, float* %arrayidx16, align 4, !tbaa !0
  %indvars.iv.next = add i64 %indvars.iv, 1
  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
  %exitcond = icmp eq i32 %lftr.wideiv, %call
  br i1 %exitcond, label %for.end, label %for.body

for.end:                                          ; preds = %for.body, %if.end
  tail call void @vector_sum(i32 %call, float* %1, float* %2, float* %3)
  br label %return

return:                                           ; preds = %entry, %for.end
  %retval.0 = phi i32 [ 0, %for.end ], [ 1, %entry ]
  ret i32 %retval.0
}

define available_externally i32 @atoi(i8* nocapture %__nptr) nounwind uwtable readonly inlinehint {
entry:
  %call = tail call i64 @strtol(i8* nocapture %__nptr, i8** null, i32 10) nounwind
  %conv = trunc i64 %call to i32
  ret i32 %conv
}

declare noalias i8* @malloc(i64) nounwind

declare double @drand48() nounwind

declare i64 @strtol(i8*, i8** nocapture, i32) nounwind

!0 = metadata !{metadata !"float", metadata !1}
!1 = metadata !{metadata !"omnipotent char", metadata !2}
!2 = metadata !{metadata !"Simple C/C++ TBAA"}
!3 = metadata !{metadata !"any pointer", metadata !1}