[LLVMdev] splat instruction
tobias at grosser.es
Thu Apr 5 08:55:04 CDT 2012
On 04/05/2012 02:50 PM, Jochen Wilhelmy wrote:
> as highlevel languages (like opencl) support operations with a vector
> on one side and a scalar on the other side (e.g. vector * scalar) it would
> be convenient if llvm ir would have a splat instruction that takes
> a scalar and produces a vector with all elements filled with the scalar.
> i assume that i'm not the first one who has this idea so what was
> the reason not to include such an instruction?
> a splat instruction would also be handy to scalarize the code as much
> as possible before outputting it again to a highlevel language.
this can be modeled like this:
%single = insertelement <1 x i32> undef, i32 %scalar, i32 0
%vector = shufflevector <1 x i32> %single, <1 x i32> undef,
<8 x i32> zeroinitializer
As any new instruction needs special treatment all over LLVM, people in
general tend to avoid new special-case instructions if the same
computation can easily be expressed with existing instructions.
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