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[GlobalISel] LegalizerHelper - Extract widenScalarAddoSubo method

Authored by porglezomp on Jan 22 2021, 1:36 PM.

Description

[GlobalISel] LegalizerHelper - Extract widenScalarAddoSubo method

The widenScalar implementation for signed and unsigned overflowing
operations were very similar: both are checked by truncating the result
and then re-sign/zero-extending it and checking that it matches the
computed operation.

Using a truncate + zero-extend for the unsigned case instead of manually
producing the AND instruction like before leads to an extra copy
instruction during legalization, but this should be harmless.

Differential Revision: https://reviews.llvm.org/D95035