cmd/compile: fold single-bit TST; CSET NE into UBFX on arm64 by gaul · Pull Request #80391 · golang/go

gaul · 2026-07-13T18:52:41Z

A boolean materialized from a single-bit test compiles to
TST $(1<<k); CSET NE. The bit is a bitfield extract: rewrite the
NotEqual of a one-bit TSTconst/TSTWconst to UBFX #k, #1, the value
form of the existing single-bit TBZ/TBNZ branch rules. The flags
producer remains for any other reader, and a shared bool's branch
then tests the extracted bit directly, so the TST disappears there
too.

Measured with armlint on darwin/arm64:

cmd/go: 166 TST; CSET pairs eliminated, __text -672 bytes.
gofmt: 35 pairs eliminated, __text -192 bytes.

gopherbot · 2026-07-13T19:16:10Z

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gopherbot · 2026-07-13T19:32:19Z

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Patch Set 1:

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gopherbot · 2026-07-13T19:48:52Z

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Patch Set 1: Commit-Queue+1

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gopherbot · 2026-07-13T19:48:53Z

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Patch Set 1:

Dry run: CV is trying the patch.

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gopherbot · 2026-07-13T19:48:54Z

Message from Keith Randall:

Patch Set 1: Auto-Submit+1 Code-Review+2 Commit-Queue+1

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gopherbot · 2026-07-13T20:06:21Z

Message from Keith Randall:

Patch Set 1: -Commit-Queue

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gopherbot · 2026-07-13T20:06:22Z

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Patch Set 1: -Commit-Queue

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gopherbot · 2026-07-13T20:06:22Z

Message from golang-scoped@luci-project-accounts.iam.gserviceaccount.com:

Patch Set 1:

This CL has failed the run. Reason:

Tryjob golang/try/gotip-linux-arm64-boringcrypto has failed with summary (view all results):

go on master (change 800241)

To reproduce, try gomote repro 8676364503023035121.

Additional links for debugging:

go tool dist test -json output [shard 2]

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gopherbot · 2026-07-13T20:06:23Z

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Patch Set 1: LUCI-TryBot-Result-1

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A boolean materialized from a single-bit test compiles to TST $(1<<k); CSET NE. The bit is a bitfield extract: rewrite the NotEqual of a one-bit TSTconst/TSTWconst to UBFX #k, golang#1, the value form of the existing single-bit TBZ/TBNZ branch rules. The flags producer remains for any other reader, and a shared bool's branch then tests the extracted bit directly, so the TST disappears there too. Measured with armlint on darwin/arm64: cmd/go: 166 TST; CSET pairs eliminated, __text -672 bytes. gofmt: 35 pairs eliminated, __text -192 bytes.

gopherbot · 2026-07-13T22:03:54Z

This PR (HEAD: 0d4f45d) has been imported to Gerrit for code review.

Please visit Gerrit at https://go-review.googlesource.com/c/go/+/800241.

Important tips:

Don't comment on this PR. All discussion takes place in Gerrit.
You need a Gmail or other Google account to log in to Gerrit.
To change your code in response to feedback:
- Push a new commit to the branch used by your GitHub PR.
- A new "patch set" will then appear in Gerrit.
- Respond to each comment by marking as Done in Gerrit if implemented as suggested. You can alternatively write a reply.
- Critical: you must click the blue Reply button near the top to publish your Gerrit responses.
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The title and description of the GitHub PR are used to construct the final commit message.
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gopherbot · 2026-07-13T22:20:33Z

Message from Andrew Gaul:

Patch Set 1:

(2 comments)

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gopherbot · 2026-07-13T22:20:34Z

Message from Keith Randall:

Patch Set 2: Commit-Queue+1

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gopherbot · 2026-07-13T22:20:34Z

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Patch Set 2:

Dry run: CV is trying the patch.

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gopherbot · 2026-07-13T22:37:36Z

Message from Keith Randall:

Patch Set 2: Auto-Submit+1 Code-Review+2

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gopherbot · 2026-07-13T22:37:37Z

Message from Keith Randall:

Patch Set 2: Code-Review+1

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gopherbot · 2026-07-13T22:53:45Z

Message from Keith Randall:

Patch Set 2: -Commit-Queue

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gopherbot · 2026-07-13T22:53:45Z

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Patch Set 2:

This CL has passed the run

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gopherbot · 2026-07-13T22:53:46Z

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Patch Set 2: LUCI-TryBot-Result+1

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gaul force-pushed the arm64/tst-cset branch from cba8fe8 to 0d4f45d Compare July 13, 2026 22:00

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gaul commented Jul 13, 2026 •

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