ir: Add Parent field to Func for its parent module

[mewmew]

This is to be consistent with ir.Block which already contains a Parent field for its parent function, and to enable further use cases of the IR API (for background, see #86 (comment)).

cc: @pwaller and @justinclift

[coveralls]

Coverage increased (+0.003%) to 67.776% when pulling cb6620c on parent into a687e6f on master.

[pwaller]

Oh dear, CI is unhappy.

[mewmew]

Oh dear, CI is unhappy.

Ah, that is to be expected. Since on of the examples (which is also run by go test) pretty-prints the IR structure, and we just added a new field to ir.Func.

Edit: the example test case has now been updated. Also, this helped us uncover that the asm parser did not instantiate the Parent field when creating new ir.Funcs, since it was not using ir.Module.NewFunc as constructor (but rather creating a struct literal). This has been fixed in cb6620c.

[mewmew]

The CI for Go 1.11 now completes successfully. For Go tip, we get the following error:

The command "go get -u github.com/golangci/golangci-lint/cmd/golangci-lint" failed and exited with 1 during .

Edit: I tried to reproduce this locally but the go get -u github.com/golangci/golangci-lint/cmd/golangci-lint command completed successfully for me using both Go 1.13 and gotip (at rev golang/go@13f179b).

[mewmew]

Since the PR is rather non-invasive and the CI for Go 1.11 is happy, I'll go ahead and merge this.