arm64: Add support for BFI and BFX instruction

[jonathandavies-arm]

This patch adds support for the Arm BFI and BFX instructions. I've added a optimisation in lowering for bit packing and unpacking using each instruction respectively.

BFI

This is used when you pack 2 or more values into an integer. e.g.
return (a & 0xf) | ((b & 0x3) << 4);
This is the node pattern it is looking for

N009 (  9, 12) [000008] -----+-----                         *  OR        int    $103
N003 (  3,  4) [000002] -----+-----                         +--*  AND       int    $100
N001 (  1,  1) [000000] -----+-----                         |  +--*  LCL_VAR   int    V00 arg0         u:1 (last use) $80
N002 (  1,  2) [000001] -c---+-----                         |  \--*  CNS_INT   int    15 $43
N008 (  5,  7) [000007] -----+-----                         \--*  LSH       int    $102
N006 (  3,  4) [000005] -----+-----                            +--*  AND       int    $101
N004 (  1,  1) [000003] -----+-----                            |  +--*  LCL_VAR   int    V01 arg1         u:1 (last use) $81
N005 (  1,  2) [000004] -c---+-----                            |  \--*  CNS_INT   int    3 $44
N007 (  1,  2) [000006] -c---+-----                            \--*  CNS_INT   int    4 $45

and changes to

     (  9, 12) [000011] -----------                         \--*  BFI       int   
N003 (  3,  4) [000002] -----+-----                            +--*  AND       int    $100
N001 (  1,  1) [000000] -----+-----                            |  +--*  LCL_VAR   int    V00 arg0         u:1 (last use) $80
N002 (  1,  2) [000001] -c---+-----                            |  \--*  CNS_INT   int    15 $43
N004 (  1,  1) [000003] -----+-----                            \--*  LCL_VAR   int    V01 arg1         u:1 (last use) $81

BFX

When you extract a continuous range of bits from an integer. This is the inverse of above. e.g.
return (x >> 5) & 0x1F;

This is the node pattern it's looking for

N005 (  5,  7) [000004] -----+-----                         \--*  AND       int    $101
N003 (  3,  4) [000002] -----+-----                            +--*  RSH       int    $100
N001 (  1,  1) [000000] -----+-----                            |  +--*  LCL_VAR   int    V00 arg0         u:1 (last use) $80
N002 (  1,  2) [000001] -----+-----                            |  \--*  CNS_INT   int    6 $42
N004 (  1,  2) [000003] -----+-----                            \--*  CNS_INT   int    63 $43

and changes to

     (  5,  7) [000007] -----------                         \--*  BFX       int   
N001 (  1,  1) [000000] -----+-----                            \--*  LCL_VAR   int    V00 arg0         u:1 (last use) $80

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[a74nh]

Spmidiff errors

[05:14:28] ISSUE: <ASSERT> #9081 /Users/runner/work/1/s/src/coreclr/jit/codegenarm64.cpp (5916) - Assertion failed '(lsb + width) <= bitWidth' in 'Microsoft.AspNetCore.Connections.CorrelationIdGenerator+<>c:<GenerateId>b__3_0(System.Span`1[char],long):this' during 'Generate code' (IL size 267; hash 0xbd4b4083; Tier1)

https://helixr1107v0xdeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-pull-123138-merge-73d1af1f3b444777be/linux-arm64-0/1/console.704b2183.log?helixlogtype=result

[jonathandavies-arm]

Spmidiff errors

[05:14:28] ISSUE: <ASSERT> #9081 /Users/runner/work/1/s/src/coreclr/jit/codegenarm64.cpp (5916) - Assertion failed '(lsb + width) <= bitWidth' in 'Microsoft.AspNetCore.Connections.CorrelationIdGenerator+<>c:<GenerateId>b__3_0(System.Span`1[char],long):this' during 'Generate code' (IL size 267; hash 0xbd4b4083; Tier1)

https://helixr1107v0xdeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-pull-123138-merge-73d1af1f3b444777be/linux-arm64-0/1/console.704b2183.log?helixlogtype=result

Fixed

[jakobbotsch]

/azp run runtime-coreclr superpmi-replay

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jakobbotsch]

Looks like there are replay failures.

[12:10:56] ISSUE: #367597 D:\a_work\1\s\src\coreclr\jit\gentree.cpp (7036) - Assertion failed 'this->OperIsBinary()' in 'System.Text.Unicode.Utf8Utility:TranscodeToUtf8(ptr,int,ptr,int,byref,byref):int' during 'LSRA allocate' (IL size 1666; hash 0xb2a9635e; FullOpts)

[jakobbotsch]

What about GT_BFI?

[jakobbotsch]

(Multiple places)

[jakobbotsch]

Please double check with another node type like GT_AND that this is being added to all the general utilities.

[jonathandavies-arm]

I think in this case the BFI is fine falling into the default case. I can't see any other cases where BFI needs something other than the default.

[jakobbotsch]

I assume bfiz is subsumed by bfi? It might be nice to replace uses of one by the other and confirm that you see no regressions.

[jonathandavies-arm]

I think BFI and BFIZ aren't similar enough to merge. I also have a another task after this is work to look into more UBFIZ/UBFX opportunities and I'd that would be better with the separate node.

[jakobbotsch]

The loop above seems to be able to match more nodes than are being removed here. I would expect that to hit asserts -- you remove some of the nodes and those nodes may have operands that you aren't marking as unused values.

Do you have test cases where the loop above matches a large number of nodes?

[jonathandavies-arm]

The test case ComposeBits_Pack32Values_Int in Bfi.cs tries to pack 32 values into an int. It converts a lot of the ors into bfi but not all of them. There are several ors at the end. The JitDump of this test case doesn't have any asserts or errors.
ComposeBits_Pack32Values_Int JitDump