[PATCH] D74632: [AArch64][SVE] Add initial backend support for FP splat_vector

[Cameron McInally via Phabricator via llvm-commits]

cameron.mcinally added a comment.

In D74632#1877178 <https://reviews.llvm.org/D74632#1877178>, @efriedma wrote:

> > There seems to be a missing lowering for f16 constants. Instead of becoming ConstantFPs, the f16 constants are being explicitly loaded from the constant pool
>
> See AArch64TargetLowering::isFPImmLegal ?  We should generate an appropriate fmov with the right target features.  I don't think "-mattr=+sve" implies those features, though.


Thanks, I'll take a look.

I also just noticed that the test file I added was renamed upstream to `sve-vector-splat.ll`. I'll move these new tests to that file.



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Comment at: llvm/lib/Target/AArch64/AArch64SVEInstrInfo.td:297
+  // Create variants of DUP_ZZI (I=0) that can be used without INSERT_SUBREG.
+  def DUP_ZV_H : Pseudo<(outs ZPR16:$Zd), (ins FPR16:$Vn), []>, Sched<[]>;
+  def DUP_ZV_S : Pseudo<(outs ZPR32:$Zd), (ins FPR32:$Vn), []>, Sched<[]>;
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efriedma wrote:
> I'm not adding a pseudo-instruction is worthwhile if the only benefit is avoiding an INSERT_SUBREG.
Good point. Will update it.

I'm not the original author (cherry-picked from D71712), so maybe I'm missing something though...


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Comment at: llvm/lib/Target/AArch64/AArch64SVEInstrInfo.td:310
+  // Duplicate +0.0 into all vector elements
+  def : Pat<(nxv8f16 (AArch64dup (f16 fpimm0))), (DUP_ZI_H 0, 0)>;
+  def : Pat<(nxv4f16 (AArch64dup (f16 fpimm0))), (DUP_ZI_H 0, 0)>;
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efriedma wrote:
> What do we end up generating for a non-zero float immediate?  We might need a pattern to avoid an extra mov in the general case.
> 
> In theory, we can generate other float immediates using the integer dup/dupm, but I guess most of them won't be useful for 32-bit or 64-bit floats.  Some probably are, though; for example, you can generate 1.0 with dupm.
I'm fairly certain that support exists in D71712. I didn't include any of the shufflevector tests or patterns in this Diff though.

My intention was to cherry-pick something small for easy reviewing. If you'd like to see that support included in this patch, I'll add it.



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