[llvm-dev] simplifycfg not happening?

[Russell Wallace via llvm-dev]

The following function compiles with -O3 into the following IR.
http://llvm.org/docs/Passes.html#simplifycfg-simplify-the-cfg says

   - Eliminates a basic block that only contains an unconditional branch.

but the first and third blocks in the compiled function only contain an
unconditional branch; I would have expected them to be eliminated. What am
I missing?

double f(double *a) {
  for (int i = 0; i < 1000; i++)
    a[i] *= 2;
  for (int i = 0; i < 1000; i++)
    a[i] *= 2;
  return a[0] + a[1];
}

; Function Attrs: nounwind uwtable
define double @"\01?f@@YANPEAN at Z"(double* nocapture %a) #1 {
overflow.checked:
  br label %vector.body, !dbg !18

vector.body:                                      ; preds = %vector.body,
%overflow.checked
  %index = phi i64 [ 0, %overflow.checked ], [ %index.next.1, %vector.body
], !dbg !18
  %0 = getelementptr inbounds double, double* %a, i64 %index, !dbg !19
  %1 = bitcast double* %0 to <2 x double>*, !dbg !20
  %wide.load = load <2 x double>, <2 x double>* %1, align 8, !dbg !20
  %2 = getelementptr double, double* %0, i64 2, !dbg !20
  %3 = bitcast double* %2 to <2 x double>*, !dbg !20
  %wide.load8 = load <2 x double>, <2 x double>* %3, align 8, !dbg !20
  %4 = fmul <2 x double> %wide.load, <double 2.000000e+00, double
2.000000e+00>, !dbg !20
  %5 = fmul <2 x double> %wide.load8, <double 2.000000e+00, double
2.000000e+00>, !dbg !20
  %6 = bitcast double* %0 to <2 x double>*, !dbg !20
  store <2 x double> %4, <2 x double>* %6, align 8, !dbg !20
  %7 = bitcast double* %2 to <2 x double>*, !dbg !20
  store <2 x double> %5, <2 x double>* %7, align 8, !dbg !20
  %index.next = or i64 %index, 4, !dbg !18
  %8 = getelementptr inbounds double, double* %a, i64 %index.next, !dbg !19
  %9 = bitcast double* %8 to <2 x double>*, !dbg !20
  %wide.load.1 = load <2 x double>, <2 x double>* %9, align 8, !dbg !20
  %10 = getelementptr double, double* %8, i64 2, !dbg !20
  %11 = bitcast double* %10 to <2 x double>*, !dbg !20
  %wide.load8.1 = load <2 x double>, <2 x double>* %11, align 8, !dbg !20
  %12 = fmul <2 x double> %wide.load.1, <double 2.000000e+00, double
2.000000e+00>, !dbg !20
  %13 = fmul <2 x double> %wide.load8.1, <double 2.000000e+00, double
2.000000e+00>, !dbg !20
  %14 = bitcast double* %8 to <2 x double>*, !dbg !20
  store <2 x double> %12, <2 x double>* %14, align 8, !dbg !20
  %15 = bitcast double* %10 to <2 x double>*, !dbg !20
  store <2 x double> %13, <2 x double>* %15, align 8, !dbg !20
  %index.next.1 = add nsw i64 %index, 8, !dbg !18
  %16 = icmp eq i64 %index.next.1, 1000, !dbg !18
  br i1 %16, label %vector.body10.preheader, label %vector.body, !dbg !18,
!llvm.loop !21

vector.body10.preheader:                          ; preds = %vector.body
  br label %vector.body10, !dbg !24

vector.body10:                                    ; preds = %vector.body10,
%vector.body10.preheader
  %index13 = phi i64 [ 0, %vector.body10.preheader ], [ %index.next21.1,
%vector.body10 ], !dbg !25
  %17 = getelementptr inbounds double, double* %a, i64 %index13, !dbg !24
  %18 = bitcast double* %17 to <2 x double>*, !dbg !26
  %wide.load26 = load <2 x double>, <2 x double>* %18, align 8, !dbg !26
  %19 = getelementptr double, double* %17, i64 2, !dbg !26
  %20 = bitcast double* %19 to <2 x double>*, !dbg !26
  %wide.load27 = load <2 x double>, <2 x double>* %20, align 8, !dbg !26
  %21 = fmul <2 x double> %wide.load26, <double 2.000000e+00, double
2.000000e+00>, !dbg !26
  %22 = fmul <2 x double> %wide.load27, <double 2.000000e+00, double
2.000000e+00>, !dbg !26
  %23 = bitcast double* %17 to <2 x double>*, !dbg !26
  store <2 x double> %21, <2 x double>* %23, align 8, !dbg !26
  %24 = bitcast double* %19 to <2 x double>*, !dbg !26
  store <2 x double> %22, <2 x double>* %24, align 8, !dbg !26
  %index.next21 = or i64 %index13, 4, !dbg !25
  %25 = getelementptr inbounds double, double* %a, i64 %index.next21, !dbg
!24
  %26 = bitcast double* %25 to <2 x double>*, !dbg !26
  %wide.load26.1 = load <2 x double>, <2 x double>* %26, align 8, !dbg !26
  %27 = getelementptr double, double* %25, i64 2, !dbg !26
  %28 = bitcast double* %27 to <2 x double>*, !dbg !26
  %wide.load27.1 = load <2 x double>, <2 x double>* %28, align 8, !dbg !26
  %29 = fmul <2 x double> %wide.load26.1, <double 2.000000e+00, double
2.000000e+00>, !dbg !26
  %30 = fmul <2 x double> %wide.load27.1, <double 2.000000e+00, double
2.000000e+00>, !dbg !26
  %31 = bitcast double* %25 to <2 x double>*, !dbg !26
  store <2 x double> %29, <2 x double>* %31, align 8, !dbg !26
  %32 = bitcast double* %27 to <2 x double>*, !dbg !26
  store <2 x double> %30, <2 x double>* %32, align 8, !dbg !26
  %index.next21.1 = add nsw i64 %index13, 8, !dbg !25
  %33 = icmp eq i64 %index.next21.1, 1000, !dbg !25
  br i1 %33, label %middle.block11, label %vector.body10, !dbg !25,
!llvm.loop !27

middle.block11:                                   ; preds = %vector.body10
  %34 = load double, double* %a, align 8, !dbg !28
  %35 = getelementptr inbounds double, double* %a, i64 1, !dbg !29
  %36 = load double, double* %35, align 8, !dbg !29
  %37 = fadd double %34, %36, !dbg !30
  ret double %37, !dbg !31
}
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150920/4ada174f/attachment.html>