Revert r152761 "Minor optimization to constant evaluation: don't bother computing expr source...", it breaks bootstrap.
Revert r152761 "Minor optimization to constant evaluation: don't bother
computing expr source...", it breaks bootstrap.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@152772 91177308-0d34-0410-b5e6-96231b3b80d8

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