[llvm-dev] Why LLVM generate two induction variables in IR level for the same induction variable in C source code

[Dong Chen via llvm-dev]

The C source code:

__kernel void adi_kernel1(__global DATA_TYPE* A, __global DATA_TYPE* B,
__global DATA_TYPE* X, int n)

{

  int i1 = get_global_id(0);

  int i2;


  if ((i1 < n))

  {

    for (i2 = 1; i2 < n; i2++)

    {

      X[i1*n + i2] = X[i1*n + i2] - X[i1*n + (i2-1)] * A[i1*n + i2] /
B[i1*n + (i2-1)];

      B[i1*n + i2] = B[i1*n + i2] - A[i1*n + i2] * A[i1*n + i2] / B[i1*n + (
i2-1)];

    }

  }

}

Only one induction variable (i2) in the source. But in the IR i2.087 and
indvars.iv are all induction variables (I think). Any body know why this
happens? Is there a way to generate only one induction variables?

; Function Attrs: nounwind ssp uwtable

define void @adi_kernel1(float* nocapture readonly %A, float* nocapture %B,
float* nocapture %X, i32 %n) #0 {

entry:

  %call = tail call i32 (i32, ...) bitcast (i32 (...)* @get_global_id to
i32 (i32, ...)*)(i32 0) #2

  %cmp = icmp slt i32 %call, %n

  %cmp186 = icmp sgt i32 %n, 1

  %or.cond = and i1 %cmp, %cmp186

  br i1 %or.cond, label %for.body.lr.ph, label %if.end


for.body.lr.ph:                                   ; preds = %entry

  %mul = mul nsw i32 %call, %n

  %sub = add i32 %mul, -1

  br label %for.body


for.body:                                         ; preds = %for.body, %
for.body.lr.ph

  %indvars.iv = phi i64 [ 1, %for.body.lr.ph ], [ %indvars.iv.next,
%for.body ]

  %i2.087 = phi i32 [ 1, %for.body.lr.ph ], [ %inc, %for.body ]

  %add = add nsw i32 %i2.087, %mul

  %idxprom = sext i32 %add to i64

  %arrayidx = getelementptr inbounds float, float* %X, i64 %idxprom

  %0 = load float, float* %arrayidx, align 4, !tbaa !8

  %1 = trunc i64 %indvars.iv to i32

  %add3 = add i32 %sub, %1

  %idxprom4 = sext i32 %add3 to i64

  %arrayidx5 = getelementptr inbounds float, float* %X, i64 %idxprom4

  %2 = load float, float* %arrayidx5, align 4, !tbaa !8

  %arrayidx9 = getelementptr inbounds float, float* %A, i64 %idxprom

  %3 = load float, float* %arrayidx9, align 4, !tbaa !8

  %mul10 = fmul float %2, %3

  %arrayidx15 = getelementptr inbounds float, float* %B, i64 %idxprom4

  %4 = load float, float* %arrayidx15, align 4, !tbaa !8

  %div = fdiv float %mul10, %4, !fpmath !12

  %sub16 = fsub float %0, %div

  store float %sub16, float* %arrayidx, align 4, !tbaa !8

  %arrayidx24 = getelementptr inbounds float, float* %B, i64 %idxprom

  %5 = load float, float* %arrayidx24, align 4, !tbaa !8

  %6 = load float, float* %arrayidx9, align 4, !tbaa !8

  %mul33 = fmul float %6, %6

  %7 = load float, float* %arrayidx15, align 4, !tbaa !8

  %div39 = fdiv float %mul33, %7, !fpmath !12

  %sub40 = fsub float %5, %div39

  store float %sub40, float* %arrayidx24, align 4, !tbaa !8

  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1

  %inc = add nuw nsw i32 %i2.087, 1

  %lftr.wideiv = trunc i64 %indvars.iv.next to i32

  %exitcond = icmp eq i32 %lftr.wideiv, %n

  br i1 %exitcond, label %if.end.loopexit, label %for.body


if.end.loopexit:                                  ; preds = %for.body

  br label %if.end


if.end:                                           ; preds =
%if.end.loopexit, %entry

  ret void

}

Thanks,

Dong
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