cmd/compile: internal compiler error: can't find source for b12->b4: v31 = MOVBload <bool> v14 v1 : DX [1.17 backport]

[gopherbot]

@randall77 requested issue #49122 to be considered for backport to the next 1.17 minor release.

@gopherbot please open a backport issue for 1.17.

[randall77]

This bug is rare but causes a serious miscompilation.

[gopherbot]

Change https://golang.org/cl/358118 mentions this issue: cmd/compile: fix fuse pass to do CFG surgery correctly

[dmitshur]

From reading #49122 I understand that this was a regression in 1.17, so 1.16 doesn't need this backport since it doesn't have the bug (please correct if that's not the case).

[randall77]

That is correct.

[gopherbot]

Closed by merging 1c05b9b to release-branch.go1.17.