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cmd/compile: Go 1.22 build fails with 1.21 PGO profile on internal/saferio change [1.22 backport] #65618

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gopherbot opened this issue Feb 8, 2024 · 2 comments
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CherryPickApproved Used during the release process for point releases compiler/runtime Issues related to the Go compiler and/or runtime.
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@gopherbot
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gopherbot commented Feb 8, 2024

@prattmic requested issue #65615 to be considered for backport to the next 1.22 minor release.

@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 gopherbot added the CherryPickCandidate Used during the release process for point releases label Feb 8, 2024
@gopherbot gopherbot added the compiler/runtime Issues related to the Go compiler and/or runtime. label Feb 8, 2024
@gopherbot gopherbot added this to the Go1.22.1 milestone Feb 8, 2024
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Change https://go.dev/cl/563016 mentions this issue: [release-branch.go1.22] cmd/compile: fail noder.LookupFunc gracefully if function generic

@thanm thanm added CherryPickApproved Used during the release process for point releases and removed CherryPickCandidate Used during the release process for point releases labels Feb 14, 2024
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Closed by merging 6cbe522 to release-branch.go1.22.

gopherbot pushed a commit that referenced this issue Feb 16, 2024
… if function generic

PGO uses noder.LookupFunc to look for devirtualization targets in
export data.  LookupFunc does not support type-parameterized
functions, and will currently fail the build when attempting to lookup
a type-parameterized function because objIdx is passed the wrong
number of type arguments.

This doesn't usually come up, as a PGO profile will report a generic
function with a symbol name like Func[.go.shape.foo]. In export data,
this is just Func, so when we do LookupFunc("Func[.go.shape.foo]")
lookup simply fails because the name doesn't exist.

However, if Func is not generic when the profile is collected, but the
source has since changed to make Func generic, then LookupFunc("Func")
will find the object successfully, only to fail the build because we
failed to provide type arguments.

Handle this with a objIdxMayFail, which allows graceful failure if the
object requires type arguments.

Bumping the language version to 1.21 in pgo_devirtualize_test.go is
required for type inference of the uses of mult.MultFn in
cmd/compile/internal/test/testdata/pgo/devirtualize/devirt_test.go.

For #65615.
Fixes #65618.

Change-Id: I84d9344840b851182f5321b8f7a29a591221b29f
Reviewed-on: https://go-review.googlesource.com/c/go/+/562737
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
(cherry picked from commit 532c6f1)
Reviewed-on: https://go-review.googlesource.com/c/go/+/563016
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