[PATCH] D146747: [RISCV] Model select and insertsubvector shuffle kinds

[Luke Lau via Phabricator via llvm-commits]

luke added inline comments.


================
Comment at: llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp:299
+    // vslideup.vi  v8, v9, 2
+    return LT.first * getLMULCost(LT.second);
+  case TTI::SK_Select: {
----------------
luke wrote:
> arcbbb wrote:
> > Thanks for implementing this!
> > I have a question: LT is from Tp, is it supposed to use SubTp instead of Tp here?
> Good point, I'm not sure. Aarch64 seems to SubTp for costing their subvector inserts. Should we be using both legalisation costs?
Using `SubTp` for the legalisation cost here gives us this diff for this test case

```
 define <8 x i64> @insert_subvector_offset_1_v8i64(<8 x i64> %v, <8 x i64> %w) {
 ; CHECK-LABEL: 'insert_subvector_offset_1_v8i64'
-; CHECK-NEXT:  Cost Model: Found an estimated cost of 4 for instruction: %res = shufflevector <8 x i64> %v, <8 x i64> %w, <8 x i32> <i32 0, i32 8, i32 9, i32 10, i32 11, i32 5, i32 6, i32 7>
+; CHECK-NEXT:  Cost Model: Found an estimated cost of 2 for instruction: %res = shufflevector <8 x i64> %v, <8 x i64> %w, <8 x i32> <i32 0, i32 8, i32 9, i32 10, i32 11, i32 5, i32 6, i32 7>
 ; CHECK-NEXT:  Cost Model: Found an estimated cost of 1 for instruction: ret <8 x i64> %res
 ;
   %res = shufflevector <8 x i64> %v, <8 x i64> %w, <8 x i32> <i32 0, i32 8, i32 9, i32 10, i32 11, i32 5, i32 6, i32 7>
   ret <8 x i64> %res
 }
```

This is what's actually generated:

```
insert_subvector_offset_1_v8i64:        # @insert_subvector_offset_1_v8i64
	.cfi_startproc
# %bb.0:
	vsetivli	zero, 5, e64, m4, tu, ma
	vslideup.vi	v8, v12, 1
	ret
```

It's using LMUL=4 here so I would presume we still want to cost it as 4 * one vslideup.


Repository:
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  https://reviews.llvm.org/D146747/new/

https://reviews.llvm.org/D146747