[LLVMdev] Error when cond of select instruction is a vector

[Fan Dawei]

Hi Rotem,

What do you mean by "you can use the <4 x float> type for which the vselect
works".

Do you mean that then back-end can correctly split the operands when it is a
four elements vector? I've try that, but it still fails.

On Wed, Oct 19, 2011 at 4:21 PM, Rotem, Nadav <nadav.rotem at intel.com> wrote:

> This is indeed a bug. I get a different error on my machine. Until we solve
> this bug, as a workaround, you can use the <4 x float> type for which the
> vselect works.  ****
>
> ** **
>
> ** **
>
> *From:* llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] *On
> Behalf Of *Fan Dawei
> *Sent:* Wednesday, October 19, 2011 10:10
> *To:* LLVMdev at cs.uiuc.edu
> *Subject:* [LLVMdev] Error when cond of select instruction is a vector****
>
> ** **
>
> Hi LLVMdev,
>
> In the specification of llvm ir, the select operation can takes a condition
> of vector type,****
> 'select' Instruction ****Syntax:****
>
>   <result> = select *selty* <cond>, <ty> <val1>, <ty> <val2>             *; yields ty*****
>
> ** **
>
>   *selty* is either i1 or {<N x i1>}****
>
> Overview:****
>
> The 'select' instruction is used to choose one value based on a condition,
> without branching.****
>
>
> If the condition is a vector of i1, then the value arguments must be
> vectors of the same size, and the selection is done element by element.
>
> However when I create a program use vector of il as the type of condition.
> The back-end fails and complains:
>
> *SplitVectorOperand Op #0: 0x2b75370: f32 = select 0x2b6c800, 0x2b75270,
> 0x2b75170 [ID=0]
>
> Do not know how to split this operator's operand!*
>
> The following program is a valid IR which passed by the checker. However
> the back-end fails on all the targets I've tested, including x86, mips and
> sparc. Is it a target independent bug?
>
>  define void @main() {
> entry:
>   %Cy300 = alloca <4 x float>
>   %Cy11a = alloca <2 x float>
>   %Cy118 = alloca <2 x float>
>   %Cy119 = alloca <2 x float>
>   br label %B1
>
> B1:                                               ; preds = %entry
>   %0 = load <2 x float>* %Cy119
>   %1 = fptosi <2 x float> %0 to <2 x i32>
>   %2 = sitofp <2 x i32> %1 to <2 x float>
>   %3 = fcmp ogt <2 x float> %0, zeroinitializer
>   %4 = fadd <2 x float> %2, <float 1.000000e+00, float 1.000000e+00>
>   %5 = select <2 x i1> %3, <2 x float> %4, <2 x float> %2
>   %6 = fcmp oeq <2 x float> %2, %0
>   %7 = select <2 x i1> %6, <2 x float> %0, <2 x float> %5
>   store <2 x float> %7, <2 x float>* %Cy118
>   %8 = load <2 x float>* %Cy118
>   store <2 x float> %8, <2 x float>* %Cy11a
>   ret void
> }
>
>
> Thanks,
> David****
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