[llvm-bugs] [Bug 48127] New: Another GEP inbound with negative offset generated by loop vectorizer

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=48127

            Bug ID: 48127
           Summary: Another GEP inbound with negative offset generated by
                    loop vectorizer
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Loop Optimizer
          Assignee: unassignedbugs at nondot.org
          Reporter: liuz at cs.utah.edu
                CC: llvm-bugs at lists.llvm.org

This one shares the same symptom with bug #48126 and might be duplicated.
However, both the code and the commandline are different from #48126, so I am
listing this bug separately.

The source comes from test case:
test/Transforms/LoopVectorize/interleaved-accesses.ll.

define void @PR27626_4(i32 *%a, i32 %x, i32 %y, i32 %z, i64 %n) {
entry:
  br label %for.body

for.body:
  %i = phi i64 [ %i.next, %for.body ], [ 0, %entry ]
  %i_plus_1 = add i64 %i, 1
  %a_i = getelementptr inbounds i32, i32* %a, i64 %i
  %a_i_plus_1 = getelementptr inbounds i32, i32* %a, i64 %i_plus_1
  store i32 %x, i32* %a_i, align 4
  store i32 %y, i32* %a_i, align 4
  store i32 %z, i32* %a_i_plus_1, align 4
  %i.next = add nuw nsw i64 %i, 2
  %cond = icmp slt i64 %i.next, %n
  br i1 %cond, label %for.body, label %for.end

for.end:
  ret void
}


Below is the vectorized function after calling opt with the arguments listed in
the test case (-loop-vectorize -instcombine -force-vector-width=4
-force-vector-interleave=1 -enable-interleaved-mem-accesses=true
-runtime-memory-check-threshold=24).

define void @PR27626_4(i32* %a, i32 %x, i32 %y, i32 %z, i64 %n) {
entry:
  %0 = icmp sgt i64 %n, 2
  %smax = select i1 %0, i64 %n, i64 2
  %1 = add nsw i64 %smax, -1
  %2 = lshr i64 %1, 1
  %3 = add nuw nsw i64 %2, 1
  %min.iters.check = icmp ult i64 %1, 6
  br i1 %min.iters.check, label %scalar.ph, label %vector.ph

vector.ph:                                        ; preds = %entry
  %n.vec = and i64 %3, 9223372036854775804
  %ind.end = shl nuw i64 %n.vec, 1
  %broadcast.splatinsert = insertelement <4 x i32> undef, i32 %y, i32 0
  %broadcast.splat = shufflevector <4 x i32> %broadcast.splatinsert, <4 x i32>
undef, <4 x i32> zeroinitializer
  %broadcast.splatinsert1 = insertelement <4 x i32> undef, i32 %z, i32 0
  %broadcast.splat2 = shufflevector <4 x i32> %broadcast.splatinsert1, <4 x
i32> undef, <4 x i32> zeroinitializer
  br label %vector.body

vector.body:                                      ; preds = %vector.body,
%vector.ph
  %index = phi i64 [ 0, %vector.ph ], [ %index.next, %vector.body ]
  %offset.idx = shl i64 %index, 1
  %4 = or i64 %offset.idx, 2
  %5 = or i64 %offset.idx, 4
  %6 = or i64 %offset.idx, 6
  %7 = or i64 %offset.idx, 1
  %8 = getelementptr inbounds i32, i32* %a, i64 %offset.idx
  %9 = getelementptr inbounds i32, i32* %a, i64 %4
  %10 = getelementptr inbounds i32, i32* %a, i64 %5
  %11 = getelementptr inbounds i32, i32* %a, i64 %6
  %12 = getelementptr inbounds i32, i32* %a, i64 -1
  store i32 %x, i32* %8, align 4
  store i32 %x, i32* %9, align 4
  store i32 %x, i32* %10, align 4
  store i32 %x, i32* %11, align 4
  %13 = getelementptr inbounds i32, i32* %12, i64 %7
  %14 = bitcast i32* %13 to <8 x i32>*
  %interleaved.vec = shufflevector <4 x i32> %broadcast.splat, <4 x i32>
%broadcast.splat2, <8 x i32> <i32 0, i32 4, i32 1, i32 5, i32 2, i32 6, i32 3,
i32 7>
  store <8 x i32> %interleaved.vec, <8 x i32>* %14, align 4
  %index.next = add i64 %index, 4
  %15 = icmp eq i64 %index.next, %n.vec
  br i1 %15, label %middle.block, label %vector.body, !llvm.loop !0

middle.block:                                     ; preds = %vector.body
  %cmp.n = icmp eq i64 %3, %n.vec
  br i1 %cmp.n, label %for.end, label %scalar.ph

scalar.ph:                                        ; preds = %middle.block,
%entry
  %bc.resume.val = phi i64 [ %ind.end, %middle.block ], [ 0, %entry ]
  br label %for.body

for.body:                                         ; preds = %for.body,
%scalar.ph
  %i = phi i64 [ %i.next, %for.body ], [ %bc.resume.val, %scalar.ph ]
  %i_plus_1 = or i64 %i, 1
  %a_i = getelementptr inbounds i32, i32* %a, i64 %i
  %a_i_plus_1 = getelementptr inbounds i32, i32* %a, i64 %i_plus_1
  store i32 %y, i32* %a_i, align 4
  store i32 %z, i32* %a_i_plus_1, align 4
  %i.next = add nuw nsw i64 %i, 2
  %cond = icmp slt i64 %i.next, %n
  br i1 %cond, label %for.body, label %for.end, !llvm.loop !2

for.end:                                          ; preds = %middle.block,
%for.body
  ret void
}

!0 = distinct !{!0, !1}
!1 = !{!"llvm.loop.isvectorized", i32 1}
!2 = distinct !{!2, !3, !1}
!3 = !{!"llvm.loop.unroll.runtime.disable"}

Here %12 is a generated gep inbound with negative offset. The source in this
transformation is more defined than target.

Alive2: https://alive2.llvm.org/ce/z/eYwaaU

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