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

[Xiangyang Guo]

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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