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cmd/compile: init info of OAS node in a select case is being dropped #48289

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danscales opened this issue Sep 9, 2021 · 3 comments
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cmd/compile: init info of OAS node in a select case is being dropped #48289

danscales opened this issue Sep 9, 2021 · 3 comments
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@danscales
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Issues exists in current master (go1.18-devel), but has probably existed for a while.

When an OAS node is converted to an OSELRECV2 node in tcSelect(), any DCL node in the Init field (due to a := assignment) is being dropped, since a completely new node is being created and the Init field was not set.

Thanks for the test case created by @mdempsky:

package main

func main() {
	ch := make(chan int, 1)

	var ptrs [2]*int
	for i := range ptrs {
		ch <- i
		select {
		case x := <-ch:
			ptrs[i] = &x
		}
	}

	for i, ptr := range ptrs {
		if *ptr != i {
			println("FAIL:", *ptr, "!=", i)
		}
	}
}
@danscales danscales self-assigned this Sep 9, 2021
@gopherbot
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Change https://golang.org/cl/348569 mentions this issue: cmd/compile: fix case where init info of OAS node is dropped

@rhysh
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rhysh commented Nov 10, 2021

The problem this fixes was introduced by 0328c3b. It affects the Go 1.17 series, including go1.17.3.

$ ./bin/go version && ./bin/go run ~/issue48289.go
go version go1.16.10 linux/amd64

$ ./bin/go version && ./bin/go run ~/issue48289.go
go version go1.17.3 linux/amd64
FAIL: 1 != 0

$ ./bin/go version && ./bin/go run ~/issue48289.go
go version devel +88e1415d08 Thu Dec 17 04:43:59 2020 +0000 linux/amd64

$ ./bin/go version && ./bin/go run ~/issue48289.go
go version devel +0328c3b660 Thu Dec 17 15:50:38 2020 +0000 linux/amd64
FAIL: 1 != 0

@gopherbot please consider this for backport to 1.17

This was referenced Nov 10, 2021
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@gopherbot
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Backport issue(s) opened: #49510 (for 1.16), #49511 (for 1.17).

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

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@rhysh @danscales @gopherbot