Review the multi-op instruction usage for Arm64

[tannergooding]

After seeing the msub PR (#66621) which folds mul, sub into a single msub I went and looked in the Arm64 manual for other interesting "combined operation" instructions.

There is a set of (shifted register) instructions which can combine a shift, op (the variants ending with s also set flags):

• add, adds - Add
• sub, subs - Subtract
• cmp - Compare #84605
• cmn - Compare Negative #84667
• neg, negs - Negate #84667
• and, ands - Bitwise AND
• bic, bics - Bitwise bit clear (@TIHan)
• eon - Bitwise exclusive OR NOT (@TIHan)
• eor - Bitwise exclusive OR
• orr - Bitwise inclusive OR
• mvn - Bitwise NOT (@TIHan)
• orn - Bitwise inclusive OR NOT (@TIHan)
• tst - Test Bits (@TIHan)

There is a set of (extended register) instructions which can combine a zero-extend, op or sign-extend, op:

• add, adds - Add
• sub, subs - Subtract
• cmp - Compare
• cmn - Compare Negative

There is a set of (carry) instructions which can utilize the carry from a previous operation:

• adc, adcs - Add with carry
• sbc, sbcs - Subtract with carry
• ngc, ngcs - Negate with carry

There are the multiply integer instructions which can combine an op, mul:

• madd - Multiply-add
• msub - Multiply-subtract
• mneg - Multiply-negate

There are then some long multiply instructions which can return a product twice the size of the inputs (i32 * i32 = i64 or similar; effectively good for covering zero or sign extend, multiply):

• smull, umull - Multiply long
• smaddl, umaddl - Multiply-add long Optimise long multiply + add/sub/neg on arm64. #91886
• smsubl, umsubl - Multiply-subtract long Optimise long multiply + add/sub/neg on arm64. #91886
• smnegl, umnegl - Multiply-negate long Optimise long multiply + add/sub/neg on arm64. #91886

Finally there is the "multiply high" instructions which can return just the upper bits of a wide multiply:

• smulh, umulh - Multiply High

There may be other interesting instructions as well, but these are ones that may have broader usage/application and which likely be good to validate we are covering

category:implementation
theme:intrinsics

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[ghost]

Tagging subscribers to this area: @JulieLeeMSFT
See info in area-owners.md if you want to be subscribed.

Issue Details

---

After seeing the msub PR (#66621) which folds mul, sub into a single msub I went and looked in the Arm64 manual for other interesting "combined operation" instructions.

There is a set of (shifted register) instructions which can combine a shift, op (the variants ending with s also set flags):

• add, adds - Add
• sub, subs - Subtract
• cmp - Compare
• cmn - Compare Negative
• neg, negs - Negate
• and, ands - Bitwise AND
• bic, bics - Bitwise bit clear
• eon - Bitwise exclusive OR NOT
• eor - Bitwise exclusive OR
• orr - Bitwise inclusive OR
• mvn - Bitwise NOT
• orn - Bitwise inclusive OR NOT
• tst - Test Bits

There is a set of (extended register) instructions which can combine a zero-extend, op or sign-extend, op:

• add, adds - Add
• sub, subs - Subtract
• cmp - Compare
• cmn - Compare Negative

There is a set of (carry) instructions which can utilize the carry from a previous operation:

• adc, adcs - Add with carry
• sbc, sbcs - Subtract with carry
• ngc, ngcs - Negate with carry

There are the multiply integer instructions which can combine an op, mul:

• madd - Multiply-add
• msub - Multiply-subtract
• mneg - Multiply-negate

There are then some long multiply instructions which can return a product twice the size of the inputs (i32 * i32 = i64 or similar):

• smull, umull - Multiply long
• smaddl, umaddl - Multiply-add long
• smsubl, umsubl - Multiply-subtract long
• smnegl, umnegl - Multiply-negate long

Finally there is the "multiply high" instructions which can return just the upper bits of a wide multiply:

• smulh, umulh - Multiply High

There may be other interesting instructions as well, but these are ones that may have broader usage/application and which likely be good to validate we are covering

Author:	tannergooding
Assignees:	-
Labels:	arch-arm64, area-CodeGen-coreclr, untriaged
Milestone:	-

[TIHan]

These look like really good optimization opportunities.

[JulieLeeMSFT]

Thanks @tannergooding for compiling all these cases. Let me put this in the future item.

[a74nh]

@tannergooding and @kunalspathak : is there anyone looking at the remaining instructions? If not, then this could be a good set of items for @SwapnilGaikwad to work through.

While doing this, it's probably worth adding some DisasmCheck tests for them too.

[kunalspathak]

@TIHan - are you planning to work on any of these?

[kunalspathak]

this could be a good set of items for @SwapnilGaikwad to work through.

Sounds good to me.

[a74nh]

MNEG support: #79550

[kunalspathak]

@a74nh - Are there more items that you or @SwapnilGaikwad will be working on?

[SwapnilGaikwad]

Hi @kunalspathak, we plan to look at the extended register instruction combinations next (add, adds, sub, subs, cmp and cmn).

[kunalspathak]

Hi @kunalspathak, we plan to look at the extended register instruction combinations next (add, adds, sub, subs, cmp and cmn).

Sounds good.

[kunalspathak]

@TIHan - Could you please update the issue description on which instructions are you planning to work on? It will help @SwapnilGaikwad to pick some other instructions to optimize.