[LLVMdev] Haswell New Instructions

[Dan Gohman]

On Jun 13, 2011, at 4:41 AM, Nicolas Capens wrote:
> 
> So I was wondering whether in LLVM a gather operation is best represented with a 'load' instruction taking vector operands, or whether it's better to define it as a separate 'gather' instruction. What would be the pros and cons of each approach, and what do you think should be the long-term goals for the LLVM instruction set?

Lots of parts of LLVM "know" about loads, and would be quite broken if
loads could suddenly be gathers.

Also, autovectorizers have to know a fair amount about target
instruction sets, especially if they're going to vectorize non-trivial things
like gathers.

So target-specific intrinsics seem like a reasonable start.  A generic
'gather' instruction/intrinsic may make sense at some point, if it can
be designed cleanly enough.

Dan

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