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cmd/loopvec-toolexec: give the same archive on every build - #15
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ubuntu-latest is now ubuntu-26.04, which has no qemu-user-static package, so every run fails at the install step and skips the arm64 tsvc run, the golden check, fmt and lint. qemu-user ships the static emulators there; link qemu-aarch64-static to it when the name is missing, as the Makefile runs that name.
Go tip writes export data in iexport version 4, which encodes float constants exactly. x/tools v0.51.0, and the v0.52.0 release, read only up to version 3, so on tip go/packages fails for every package: cannot import "math" (unstable iexport format version 4, just rebuild compiler and std library), export data is newer version - update tool and every script that runs loopvec fails in the tip job. x/tools master reads version 4 (golang/tools@966056e2637c). Update to it until a release includes it. The pinned toolchain is unaffected.
go1.27.3 is the latest 1.27 release. Its simd package is the same as go1.27.1's, so the capability table only changes in its header, and the -methods crash (golang/go#80657) is still there, as flag_methods_ice.txt checks. go.mod keeps go 1.27.1: that is the first release whose simd package loopvec's output compiles against (go1.27.0's ShiftAllRight takes a uint8).
The wrapper wrote the rewritten files to a new os.MkdirTemp directory under the go command's work directory. The compiler records file names in the export data, and the go command trims only the compile's own object directory, so every build of a rewritten package produced a different archive, with a random absolute path in it. That fails builds where the go command compiles a package twice with the same inputs. With PGO, go test can compile a dependency once for each test binary that needs it, then compile an importer against one copy and link the other. In github.com/thesyncim/goav1, whose cmd/qualitybench has a default.pgo, go test ./... fails with: link: fingerprint mismatch: github.com/thesyncim/goav1 has 9bcecb47ca806e38, import from github.com/thesyncim/goav1/cmd/qualitybench expecting 224b81cee36e8b4e The rewritten files now go in a loopvec directory inside the object directory, next to the importcfg the go command writes there. That is still a separate place for each compile, and the -trimpath the go command passes reduces it to loopvec/x.go.
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Stacked on #4.
The wrapper wrote rewritten files to a fresh
os.MkdirTempdirectory under the go command's work directory. File names end up in the export data, and the go command only trims each compile's own object directory. So every build of a rewritten package gave a different archive, with a random absolute path in it.That breaks builds where the go command compiles one package twice with the same inputs. With PGO,
go testcan compile a dependency once per test binary, then compile an importer against one copy and link the other. In goav1, whosecmd/qualitybenchhas adefault.pgo,go test ./...failed with master's wrapper:The rewritten files now go in
loopvec/inside the object directory, next to the importcfg the go command writes there. That's still a separate place for each compile, and the-trimpath "$WORK/bNNN=>"that the go command always passes reduces it toloopvec/x.go. After this, the two archives in that build have the same content ID, and the test binary links.toolexec_reproducible.txtbuilds a package with two empty caches and compares the archives. It fails without the change.-trimpathbuilds were already fine.