[LLVMdev] How to use ConstantFoldConstantExpression?

[ihusar]

I forgot to mention, that I use LLVM release 2.8, I did not try it with the latest revision, but I expect that I
am rather doing something wrong than using non-implemented functions.

On Tue, 15 Feb 2011 14:09:57 +0100, ihusar <ihusar at fit.vutbr.cz> wrote:

> Hello,
>
>    i need to fold constants, i found that a function ConstantFoldConstantExpression could be used,
> however I am not able to make it fold anything. Could you please give me some advice, what I am doing wrong?
>
>
> My code looks something like this:
>
> //data layout is obtained from clang-generated code for triple arm-none-linux-gnueabi with added v32:32:32
> const char* const TARGET_DATA_LAYOUT =
> 	"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v32:32:32-v64:64:64-v128:128:128-a0:0:64-n32";
>
> TargetData TD(TARGET_DATA_LAYOUT);
>
> void transformConstantExpr(ConstantExpr* cop)
> {
>    Constant* val = ConstantFoldConstantExpression(cop, &TD);
>    if (val != NULL)
>    {
>   	errs() << "**" << *cop << " to \n--" << *val << "\n";
>    }
> }
>
> And this is the output i get, all constants should result in "i32 0" (at least this is what I need):
>
> **i32 bitcast (<4 x i8> zeroinitializer to i32) to
> --i32 bitcast (<4 x i8> zeroinitializer to i32)
>
> **i32 sext (i8 trunc (i32 bitcast (<4 x i8> zeroinitializer to i32) to i8) to i32) to
> --i32 sext (i8 trunc (i32 bitcast (<4 x i8> zeroinitializer to i32) to i8) to i32)
>
> **i32 bitcast (<4 x i8> <i8 trunc (i32 shl (i32 sext (i8 trunc (i32 bitcast (<4 x i8> zeroinitializer to i32) to i8) to i32), i32 0) to i8), i8 0, i8 0, i8 0> to i32) to
> --i32 bitcast (<4 x i8> <i8 trunc (i32 shl (i32 sext (i8 trunc (i32 bitcast (<4 x i8> zeroinitializer to i32) to i8) to i32), i32 0) to i8), i8 0, i8 0, i8 0> to i32)
>
> **i32 and (i32 bitcast (<4 x i8> zeroinitializer to i32), i32 255) to
> --i32 and (i32 bitcast (<4 x i8> zeroinitializer to i32), i32 255)
>
> **i32 bitcast (<4 x i8> <i8 trunc (i32 lshr (i32 and (i32 bitcast (<4 x i8> zeroinitializer to i32), i32 255), i32 0) to i8), i8 0, i8 0, i8 0> to i32) to
> --i32 bitcast (<4 x i8> <i8 trunc (i32 lshr (i32 and (i32 bitcast (<4 x i8> zeroinitializer to i32), i32 255), i32 0) to i8), i8 0, i8 0, i8 0> to i32)
>
> **i32 bitcast (<4 x i8> <i8 trunc (i32 bitcast (<4 x i8> zeroinitializer to i32) to i8), i8 0, i8 0, i8 0> to i32) to
> --i32 bitcast (<4 x i8> <i8 trunc (i32 bitcast (<4 x i8> zeroinitializer to i32) to i8), i8 0, i8 0, i8 0> to i32)
>
> **i32 bitcast (<2 x i16> zeroinitializer to i32) to
> --i32 bitcast (<2 x i16> zeroinitializer to i32)
>
> **i32 bitcast (<4 x i8> bitcast (i32 bitcast (<2 x i16> <i16 zext (i8 extractelement (<4 x i8> bitcast (i32 bitcast (<4 x i8> zeroinitializer to i32) to <4 x i8>), i32 2) to i16), i16 zext (i8 extractelement (<4 x i8> bitcast (i32 bitcast (<4 x i8> zeroinitializer to i32) to <4 x i8>), i32 3) to i16)> to i32) to <4 x i8>) to i32) to
> --i32 bitcast (<4 x i8> bitcast (i32 bitcast (<2 x i16> <i16 zext (i8 extractelement (<4 x i8> bitcast (i32 bitcast (<4 x i8> zeroinitializer to i32) to <4 x i8>), i32 2) to i16), i16 zext (i8 extractelement (<4 x i8> bitcast (i32 bitcast (<4 x i8> zeroinitializer to i32) to <4 x i8>), i32 3) to i16)> to i32) to <4 x i8>) to i32)
>
>
> Have I something wrong in the TargetData or do I miss something else?
> I tried also big endian, but it did not help.
>
> Thank you
>    Adam Husar
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev