[PATCH] D116479: [VPlan] Introduce and use BranchOnCount VPInstruction.

[Bardia Mahjour via Phabricator via llvm-commits]

bmahjour added a comment.

This commit somehow causes the "unroll.disable" metadata to be dropped from the vector epilogue loops. For example:

  > cat tmp.ll
  target datalayout = "e-m:e-i64:64-n32:64"
  target triple = "powerpc64le-unknown-linux-gnu"
  
  ; Function Attrs: nounwind
  define dso_local void @f1(float* noalias %aa, float* noalias %bb, float* noalias %cc, i32 signext %N) #0 {
  entry:
    %cmp1 = icmp sgt i32 %N, 0
    br i1 %cmp1, label %for.body.preheader, label %for.end
  
  for.body.preheader:                               ; preds = %entry
    %wide.trip.count = zext i32 %N to i64
    br label %for.body
  
  for.body:                                         ; preds = %for.body.preheader, %for.body
    %indvars.iv = phi i64 [ 0, %for.body.preheader ], [ %indvars.iv.next, %for.body ]
    %arrayidx = getelementptr inbounds float, float* %bb, i64 %indvars.iv
    %0 = load float, float* %arrayidx, align 4
    %arrayidx2 = getelementptr inbounds float, float* %cc, i64 %indvars.iv
    %1 = load float, float* %arrayidx2, align 4
    %add = fadd fast float %0, %1
    %arrayidx4 = getelementptr inbounds float, float* %aa, i64 %indvars.iv
    store float %add, float* %arrayidx4, align 4
    %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
    %exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count
    br i1 %exitcond, label %for.body, label %for.end.loopexit
  
  for.end.loopexit:                                 ; preds = %for.body
    br label %for.end
  
  for.end:                                          ; preds = %for.end.loopexit, %entry
    ret void
  }



  opt -passes=loop-vectorize ./tmp.ll -S -o out.ll -epilogue-vectorization-force-VF=2



  > grep "!" out.ll
    br i1 %132, label %middle.block, label %vector.body, !llvm.loop !0
    br i1 %144, label %vec.epilog.middle.block, label %vec.epilog.vector.body, !llvm.loop !2
    br i1 %exitcond, label %for.body, label %for.end.loopexit.loopexit, !llvm.loop !3
  !0 = distinct !{!0, !1}
  !1 = !{!"llvm.loop.isvectorized", i32 1}
  !2 = distinct !{!2, !1}
  !3 = distinct !{!3, !4, !1}
  !4 = !{!"llvm.loop.unroll.runtime.disable"}

Previously we had:

  ...
    br i1 %144, label %vec.epilog.middle.block, label %vec.epilog.vector.body, !llvm.loop !2
  ...
  !2 = distinct !{!2, !3, !1}
  !3 = !{!"llvm.loop.unroll.runtime.disable"}


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D116479/new/

https://reviews.llvm.org/D116479