[LLVMdev] How to use ConstantFoldConstantExpression?

[Duncan Sands]

Hi,

> 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.

the constant folder has historically done a poor job of folding vector
expressions.  Does it succeed in folding non-vector expressions?

Ciao, Duncan.

>
> 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
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