[LLVMdev] LSR pass

[Jonas Paulsson]

Hi,

I would like some help regarding the LSR pass. It seems that it likes to duplicate address calculations as in the case above, which is highly undesirable on my target.

I wonder if there is any way to tell LSR to not duplicate the code in cases like this? Or could I perhaps run CSE after LSR again?
What is the logic behind this transformation? It seems that a LSR pass should not insert a multiplication, generally..?

Thanks,
Jonas



  %_tmp44 = ptrtoint i16* par1 to i16
  %_tmp51 = ptrtoint i16* par2 to i16
...
inside loop:
*** IR Dump After Canonicalize natural loops ***
bb7: (header)                                     ; preds = %bb7.lr.ph, %bb11

  %_tmp39 = sub i16 %_tmp35, %_tmp38
  %2      = mul i16 %_tmp39, -10
  %_tmp41 = add i16 %2, %subframeCount.12.014

  %_tmp45 = add i16 %_tmp41, %_tmp44
  %_tmp46 = inttoptr i16 %_tmp45 to i16*
  %_tmp47 = load i16* %_tmp46, align 1


bb8:                                              ; preds = %bb7
  %_tmp52 = add i16 %_tmp41, %_tmp51
  %_tmp53 = inttoptr i16 %_tmp52 to i16*
  %_tmp54 = load i16* %_tmp53, align 1

...
  br i1 %_tmp64, label %bb7, label %bb13.loopexit
(latch)

*** IR Dump After Loop Strength Reduction ***
bb7:                                              ; preds = %bb7.lr.ph, %bb11

  %_tmp39 = sub i16 %_tmp35, %_tmp38
  %2 = mul i16 %_tmp39, -10
  %3 = add i16 %_tmp44, %subframeCount.12.014
  %4 = add i16 %3, %2
  %_tmp46 = inttoptr i16 %4 to i16*
  %_tmp47 = load i16* %_tmp46, align 1

bb8:                                              ; preds = %bb7
  %5 = sub i16 %_tmp35, %_tmp38
  %6 = mul i16 %5, -10
  %7 = add i16 %_tmp51, %subframeCount.12.014
  %8 = add i16 %7, %6
  %_tmp53 = inttoptr i16 %8 to i16*
  %_tmp54 = load i16* %_tmp53, align 1

...
  br i1 %_tmp64, label %bb7, label %bb13.loopexit
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