cmd/compile: Go 1.22 build fails with 1.21 PGO profile on internal/saferio change

[konradreiche]

Go version

go version go1.22.0 linux/amd64

Output of go env in your module/workspace:

GOARCH='amd64'
GOOS='linux'
GOVERSION='go1.22.0'

What did you do?

We are continuously collecting PGO profiles and apply them to new builds, a process that worked seamlessly with Go 1.21. I upgraded to Go 1.22 and attempted to compile our build using the Go 1.21 PGO profile.

go build -pgo=auto .

What did you see happen?

The go build command failed, producing the following error:

go build -pgo=auto .
# encoding/gob
/usr/lib/go/src/bufio/bufio.go:47:6: internal compiler error: saferio.SliceCap has 0+1 params, but instantiated with 0+0 args

This error suggests a change made to the SliceCap method in the internal/saferio package between Go 1.21 and Go 1.22:

https://github.com/golang/go/blob/release-branch.go1.21/src/internal/saferio/io.go#L116
https://github.com/golang/go/blob/release-branch.go1.22/src/internal/saferio/io.go#L128

The build compiles successfully with PGO turned off:

go build -pgo=off .

What did you expect to see?

Expected the go build command to compile the build successfully, as it did with Go 1.21.

[konradreiche]

I assume this isn't expected because according to the PGO documentation a change to the source code could result in performance degradation but not necessarily compilation failure.

[prattmic]

Thanks for filing this! We discovered this same crash with a different symbol independently this morning and I was coming to file an issue only to find you've done so for me. :D

This is indeed a bug in the way we lookup functions for PGO. Internally, the compiler internally is trying to look up the function as non-generic (because the profile contains the non-generic symbol name), but the function is actually generic and the compiler chokes. We should fix this.

[prattmic]

@gopherbot Please backport to 1.21 and 1.22. This is a build failure with PGO if a hot function is changed from non-generic to generic. Only workarounds are to rename the symbol or disable PGO.

[gopherbot]

Backport issue(s) opened: #65617 (for 1.21), #65618 (for 1.22).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

[gopherbot]

Change https://go.dev/cl/562737 mentions this issue: cmd/compile: fail noder.LookupFunc gracefully if function generic

[gopherbot]

Change https://go.dev/cl/563016 mentions this issue: [release-branch.go1.22] cmd/compile: fail noder.LookupFunc gracefully if function generic