[PATCH] ARM/NEON: Improve codegen for long sext/zext operations.

[Renato Golin]

On 16 March 2013 02:51, Pete Couperus <pjcoup at gmail.com> wrote:

> Thanks for the review.  I'd be happy to modify the cost values.
> Is there a guideline for what this should be?  I surmise looking at
> the comments and the other entries that this isn't quite as simple as
> something like the number of vmovl's.  Or should I just remove the
> entries corresponding to the cases covered in the patch?
>

Hi Pete,

The costs for the operations you're changing are:

+    setOperationAction(ISD::SIGN_EXTEND, MVT::v8i32,  Custom);
+    setOperationAction(ISD::ZERO_EXTEND, MVT::v8i32,  Custom);
+    setOperationAction(ISD::SIGN_EXTEND, MVT::v16i32, Custom);
+    setOperationAction(ISD::ZERO_EXTEND, MVT::v16i32, Custom);

They don't have specific entries (AFAICS) in the cost tables, so it ends up
just exploding the cost. Fair enough, they were a bunch of strh
instructions.

What you have to do is to add entries in ARMTargetTransformInfo.cpp ->
ARMTTI::getCastInstrCost() like:

    { ISD::SIGN_EXTEND, MVT::v16i64, MVT::v16i32, 4 },
    { ISD::ZERO_EXTEND, MVT::v16i64, MVT::v16i32, 4 },
    { ISD::SIGN_EXTEND, MVT::v8i64, MVT::v8i32, 3 },
    { ISD::ZERO_EXTEND, MVT::v8i64, MVT::v8i32, 3 },

---> Arnold, please correct me if I'm wrong <---

And the ones you're adding new:

+    setOperationAction(ISD::SIGN_EXTEND, MVT::v4i64,  Custom);
+    setOperationAction(ISD::ZERO_EXTEND, MVT::v4i64,  Custom);
+    setOperationAction(ISD::SIGN_EXTEND, MVT::v8i64,  Custom);
+    setOperationAction(ISD::ZERO_EXTEND, MVT::v8i64,  Custom);

That need similar entries on the table in ARMTTI taking each instruction as
an ideal cost of 1.

Format is { ISD, DestType, SourceType, Cost };

That should improve some vectorized benchmarks, but I don't expect it to
show above the noise level in LNT, so let's look for correctness rather
than performance for now.

cheers,
--renato
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