[PATCH]Clang and AArch64 backend patches to support sshll/ushll instructions

[Hao Liu]

Hi Tim,

I'm just confused about the reusable duplicate node.

I think shift left, signed shift right and unsigned shift right are different, so there are ISD::SHL, ISD::SRA and ISD::SRL operations. As a result, we need at least 3 different NEON_SHLIMM, NEON_USHRIMM and NEON_SSHRIMM to distinguish the differences.
You mean to use an operation like NEON_DUPimm, but I don't know how to distinguish whether it shifts left or right. Do you mean I can use the combination of ISD::SHL and NEON_DUPimm? But ISD::SHL require two vectors and no immediate value.  Could you please give me an example to explain how to use it?

Thanks,
-Hao

-----Original Message-----
From: Tim Northover [mailto:t.p.northover at gmail.com]
Sent: Wednesday, August 14, 2013 5:15 PM
To: Hao Liu
Cc: llvm-commits; Ana Pazos; Jiangning Liu
Subject: Re: [PATCH]Clang and AArch64 backend patches to support sshll/ushll instructions

Hi Hao,

Looking very nice! Thanks for working on those changes, they were rather substantial.

> (1)  Use IR (sext/zext, shufflevector and shl) to implement the ACLE
> functions. As I also use shift left by immediate instruction, I also add support for the shl instruction.

I think one minor change would make this more generic. Instead of creating NEON_SHLIMM, couldn't you create a normal ISD::SHL operation where the right-hand side is (say) (NEON_DUP imm)? Then when we get around to implementing things like USHR we can just reuse that duplicate node instead of adding more NEON_SHRIMM nodes.

> As I haven't find a better way to implement this, I don't modify this code yet.

Ok, I think I'm happy with that for now.

Other than that, just one minor nit:

+  if (! BVN || ! BVN->isConstantSplat(SplatBits, SplatUndef,
+ SplatBitSize,

I don't think we normally put a space between '!' and its operand.
There are some other places with this too.

Cheers.

Tim.


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