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The Wire · Showcase

AMD64 COMPILER BUG FIXED AFTER MISSCOMPILATION REPORTS

By RepoJournal · Filed · About Go

The Go compiler shipped a critical fix for an AMD64 code generation bug that was producing incorrect conditional logic in compiled binaries.

The cmd/compile team patched a backwards mapping in AMD64 SETcc and Jcc conditional code handling [1] that was causing the compiler to generate wrong machine code. The bug was in special-case floating-point conditional logic where SETGF and SETGEF instructions were mapped incorrectly, flipping the semantics of conditional branches. This is the kind of subtle compiler bug that can slip past unit tests but break production code in hard-to-debug ways. The fix also prompted a broader concern: the conditional code tables are documented as "extremely error prone" and the team is revisiting deeper architectural improvements [1]. In parallel, the codegen test suite was updated to reflect fixes in slice backing store analysis [2], ensuring the test infrastructure keeps pace with compiler improvements.

Action items

References

  1. [1] cmd/compile: fix AMD64 misscompilation due to AMD64 SETcc and Jcc mapping golang/go
  2. [2] test/codegen: update runtimefreegc test for slice backing store fix golang/go

FAQ

What changed in Go on June 14, 2026?
The Go compiler shipped a critical fix for an AMD64 code generation bug that was producing incorrect conditional logic in compiled binaries.
What should Go teams do about it?
Rebuild any AMD64 binaries compiled with recent Go versions and validate conditional logic behavior • Monitor for Go release that includes the AMD64 fix and plan an upgrade
Which Go repositories shipped on June 14, 2026?
golang/go

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