arm64: Add support for BFI and BFX instruction by jonathandavies-arm · Pull Request #123138 · dotnet/runtime

jonathandavies-arm · 2026-01-13T16:03:59Z

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

dotnet-policy-service · 2026-01-13T16:05:13Z

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

a74nh · 2026-01-26T16:43:48Z

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

- Remove Expect.cs

jonathandavies-arm · 2026-01-29T10:40:22Z

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 · 2026-02-13T11:18:33Z

/azp run runtime-coreclr superpmi-replay

azure-pipelines · 2026-02-13T11:18:54Z

Azure Pipelines successfully started running 1 pipeline(s).

jakobbotsch · 2026-02-13T13:13:23Z

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 · 2026-03-03T15:27:05Z

src/coreclr/jit/gentree.cpp

+#ifdef TARGET_ARM64
+        case GT_BFX:
+            if (operand == this->AsOp()->gtOp1)
+            {
+                *pUse = &this->AsOp()->gtOp1;
+                return true;
+            }
+            return false;
+#endif


What about GT_BFI?

(Multiple places)

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

jakobbotsch · 2026-03-03T15:29:09Z

src/coreclr/jit/codegenarm64.cpp

+{
+    assert(tree->OperIs(GT_BFI));
+
+    GenTreeBfm* bfm = tree->AsBfm();


We could just take GenTreeBfm*

jakobbotsch · 2026-03-03T15:30:15Z

src/coreclr/jit/gentree.cpp

+{
+    GenTreeBfm* result = new (this, GT_BFI) GenTreeBfm(GT_BFI, type, base, src, offset, width);
+    result->gtFlags |= (base->gtFlags | src->gtFlags) & (GTF_ALL_EFFECT);
+    result->gtFlags &= ~GTF_SET_FLAGS;


Suggested change

result->gtFlags &= ~GTF_SET_FLAGS;

Unnecessary?

jakobbotsch · 2026-03-03T15:30:22Z

src/coreclr/jit/gentree.cpp

+{
+    GenTreeBfm* result = new (this, GT_BFX) GenTreeBfm(GT_BFX, type, base, nullptr, offset, width);
+    result->gtFlags |= (base->gtFlags & GTF_ALL_EFFECT);
+    result->gtFlags &= ~GTF_SET_FLAGS;


Suggested change

result->gtFlags &= ~GTF_SET_FLAGS;

jakobbotsch · 2026-03-03T15:31:56Z

src/coreclr/jit/gtlist.h

+GTNODE(BFI              , GenTreeBfm         ,0,0,GTK_BINOP|GTK_EXOP|DBK_NOTHIR) // Bitfield Insert.
 GTNODE(BFIZ             , GenTreeOp          ,0,0,GTK_BINOP|DBK_NOTHIR) // Bitfield Insert in Zero.
+GTNODE(BFX              , GenTreeBfm         ,0,0,GTK_UNOP|GTK_EXOP|DBK_NOTHIR) // Bitfield Extract.


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.

jakobbotsch · 2026-03-03T15:36:00Z

src/coreclr/jit/lower.cpp

+            baseMaskKnown = false;
+            break;
+        }
+    }


This seems like it needs some interference checks (via IsInvariantInRange). The values being evaluated at the original node locations may change when you are evaluating them in a new node location if you don't check for interference.

jakobbotsch · 2026-03-03T15:36:25Z

src/coreclr/jit/lower.cpp

+    bfm->CopyCosts(tree);
+


Suggested change

bfm->CopyCosts(tree);

Don't think that's necessary.

jakobbotsch · 2026-03-03T15:38:10Z

src/coreclr/jit/lower.cpp

+    LIR::Use use;
+    if (BlockRange().TryGetUse(tree, &use))
+    {
+        use.ReplaceWith(bfm);
+    }


Suggested change

LIR::Use use;

if (BlockRange().TryGetUse(tree, &use))

{

use.ReplaceWith(bfm);

}

LIR::Use use;

if (BlockRange().TryGetUse(tree, &use))

{

use.ReplaceWith(bfm);

}

else

{

bfm->SetUnusedValue();

}

Value-producing nodes without users need to be set as unused. If tree was unused, your transformation is also leaving bfm unused.

jakobbotsch · 2026-03-03T15:42:01Z

src/coreclr/jit/lower.cpp

+            return false;
+    }
+
+    BlockRange().Remove(tree);


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?

github-actions bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Jan 13, 2026

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Jan 13, 2026

arm64: Add GT_BFI node

6e6573a

jonathandavies-arm force-pushed the upstream/co/bitfield-manipulation branch from ce512bf to 1a8d58f Compare January 19, 2026 11:18

build-analysis bot mentioned this pull request Jan 19, 2026

Cannot find 'arm64-v8a' device dotnet/dnceng#2284

Open

3 tasks

arm64: Add GT_BFX node

83a6004

jonathandavies-arm force-pushed the upstream/co/bitfield-manipulation branch from 1a8d58f to 83a6004 Compare January 21, 2026 09:21

Fix bug when creating a Bfx node if the width + offset > bitwidth

1f98a79

- Remove Expect.cs

build-analysis bot mentioned this pull request Jan 29, 2026

System.IO.Tests.Directory_Create_Tests.FileSystemWatcher_Directory_Create_InNestedDirectory fails with "Created event did not occur as expected" #103630

Open

jonathandavies-arm added 2 commits February 5, 2026 10:45

Merge branch 'main' into upstream/co/bitfield-manipulation

8239a55

Rename comp to m_compiler

4c4f3b3

build-analysis bot mentioned this pull request Feb 5, 2026

Failing test due to no detected IO events in 'System.IO.Tests.FileSystemWatcherTest.ExecuteAndVerifyEvents' #103584

Open

Merge branch 'main' into upstream/co/bitfield-manipulation

6744dcb

This was referenced Feb 10, 2026

Test failure: baseservices/exceptions/stackoverflow/stackoverflowtester/stackoverflowtester.cmd #110173

Open

crossgen2 failing on Linux Arm32 intermittently #124007

Closed

Merge branch 'main' into upstream/co/bitfield-manipulation

282bbdf

This was referenced Feb 11, 2026

[Android][CoreCLR] System.Security.Cryptography.Tests killed by lowmemorykiller #118603

Open

System.Security.Cryptography.CryptographicException : m_safeCertContext is an invalid handle. #124279

Closed

jakobbotsch self-requested a review February 12, 2026 18:15

Merge branch 'main' into upstream/co/bitfield-manipulation

026487a

build-analysis bot mentioned this pull request Feb 23, 2026

[android][clr] No peer certificates when executing System.Net.Http.Functional.Tests on Android emulator #124526

Open

Handle TryGetUse() correctly for a BFX node

17dab93

jakobbotsch closed this Feb 27, 2026

jakobbotsch reopened this Feb 27, 2026

build-analysis bot mentioned this pull request Feb 27, 2026

"We stopped hearing from agent Azure Pipelines 32. Verify the agent machine is running and has a healthy network connection" dotnet/dnceng#1886

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3 tasks

jakobbotsch reviewed Mar 3, 2026

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jonathandavies-arm commented Jan 13, 2026

BFI

BFX

Uh oh!

dotnet-policy-service bot commented Jan 13, 2026

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a74nh commented Jan 26, 2026

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jonathandavies-arm commented Jan 29, 2026

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jakobbotsch commented Feb 13, 2026

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