[LLVMdev] remove redundant load by GVN() does not work

[Daniel Berlin]

Add basicaa.  Without aa, it won't touch these

On Sat, Apr 18, 2015, 8:33 PM Xiangyang Guo <xguo6 at ncsu.edu> wrote:

> Hi,
>
> Assume I have the following code. The first four instructions in each BB
> does the same thing. So I think GVN() can remove the redundant code.
> However, after I apply GVN to my module by "Passes.add(createGVNPass())"
> and  "Passes.run(*myModule)". It seems GVN does not remove the redundant
> instructions. Can anyone give me a hint what's going on here? Any hint is
> appreciable.
>
> *********************************************************************
> cond_3:                                           ; preds = %cond_1_else
>   %a1 = load i32** @a
>   %v41 = load i32* %v4
>   %6 = getelementptr i32* %a1, i32 %v41
>   %7 = load i32* %6
>   %8 = icmp slt i32 %7, 1
>   br i1 %8, label %cond_4, label %cond_4_else
>
> cond_4_else:                                      ; preds = %cond_3
>   %a2 = load i32** @a
>   %v42 = load i32* %v4
>   %9 = getelementptr i32* %a2, i32 %v42
>   %10 = load i32* %9
>   %11 = icmp sgt i32 %10, %v6_int_34
>   br i1 %11, label %cond_4, label %cond_4_else1
>
> cond_4_else1:                                     ; preds = %cond_4_else
>   %a3 = load i32** @a
>   %v43 = load i32* %v4
>   %12 = getelementptr i32* %a3, i32 %v43
>   %13 = load i32* %12
>   %v5_int_42 = srem i32 %v2_int_.0, %13
>   %14 = icmp eq i32 %v5_int_42, 0
>   br i1 %14, label %cond_4_else2, label %cond_4
>
> ************************************************************************
> (I change the variable's name a little bit for the first four instructions
> in each BB because the name of variables in my original IR has a long.)
>
> Regards
>
> Xiangyang
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