[PATCH] D77635: [LV] Vectorize with FoldTail when Primary Induction is absent

[Serguei Katkov via Phabricator via llvm-commits]

skatkov added a comment.

Hello @Ayal, unfortunately this patch causes the functional regression.
For the test below, vectorizer decided to vectorize inner loop by 32 while it has only a couple of iteration and it causes a miscompile.
Please fix it quickly or revert the patch.

The reproducer:

  ; ModuleID = './repro.ll'
  source_filename = "./repro.ll"
  target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128-ni:1-p2:32:8:8:32-ni:2"
  target triple = "x86_64-unknown-linux-gnu"
  
  @global = external global i8*
  
  define void @hoge(i8* nonnull align 8 dereferenceable_or_null(8) %arg, i8* align 8 dereferenceable_or_null(16) %arg1) {
  bb:
    %tmp = load atomic i8*, i8** @global unordered, align 8
    %tmp2 = getelementptr inbounds i8, i8* %tmp, i64 852
    br label %bb3
  
  bb3:                                              ; preds = %bb12, %bb
    %tmp4 = phi i32 [ 1, %bb ], [ %tmp15, %bb12 ]
    %tmp5 = phi i32 [ 0, %bb ], [ %tmp8, %bb12 ]
    br label %bb7
  
  bb6:                                              ; preds = %bb12
    ret void
  
  bb7:                                              ; preds = %bb7, %bb3
    %tmp8 = phi i32 [ %tmp5, %bb3 ], [ %tmp10, %bb7 ]
    %tmp9 = phi i32 [ 1, %bb3 ], [ %tmp10, %bb7 ]
    %tmp10 = add nuw nsw i32 %tmp9, 1
    %tmp11 = icmp ugt i32 %tmp9, 5
    br i1 %tmp11, label %bb12, label %bb7
  
  bb12:                                             ; preds = %bb7
    %tmp13 = mul i32 %tmp8, %tmp4
    %tmp14 = trunc i32 %tmp13 to i8
    fence release
    store atomic i8 %tmp14, i8* %tmp2 unordered, align 1
    fence seq_cst
    %tmp15 = add nuw nsw i32 %tmp4, 1
    %tmp16 = icmp ult i32 %tmp4, 240
    br i1 %tmp16, label %bb3, label %bb6
  }

ran as

  > opt -passes=loop-vectorize -S -o res.ll ./repro.ll


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D77635/new/

https://reviews.llvm.org/D77635