cmd/compile: crash on pointer conversion in call to mapaccess2 [1.18 backport]

[gopherbot]

@ianlancetaylor requested issue #51840 to be considered for backport to the next 1.18 minor release.

@gopherbot Please open a backport to 1.18

This is a compiler crash on valid code.

[mdempsky]

On #51840, it's reported that 115c3bf happened to fix this issue. I think that CL will backport cleanly to 1.18, but I think it will break -G=0 mode.

If we want to fix for 1.18, I can prepare a backport fix that doesn't break -G=0. It would be just keeping the old logic for -G=0, and the new logic for -G=3 and unified IR.

[gopherbot]

Change https://go.dev/cl/405436 mentions this issue: [release-branch.go1.18] cmd/compile: backport fix for #51840

[heschi]

Crash on valid code. Approved.

[gopherbot]

Closed by merging e1b14f5 to release-branch.go1.18.