[InstSimplify] Fix addo/subo undef folds (PR42209)
Fix folds of addo and subo with an undef operand to be:
`@llvm.{u,s}{add,sub}.with.overflow` all fold to `{ undef, false }`,
as per LLVM undef rules.
Same for commuted variants.
Based on the original version of the patch by @nikic.
Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=42209 | PR42209 ]]
Differential Revision: https://reviews.llvm.org/D63065
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@363522
91177308-0d34-0410-b5e6-
96231b3b80d8
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