[ValueTracking][X86] Compute KnownBits for phadd/phsub (#92429)
Add KnownBits computations to ValueTracking and X86 DAG lowering.
These instructions add/subtract adjacent vector elements in their operands. Example: phadd [X1, X2] [Y1, Y2] = [X1 + X2, Y1 + Y2]. This means that, in this example, we can compute the KnownBits of the operation by computing the KnownBits of [X1, X2] + [X1, X2] and [Y1, Y2] + [Y1, Y2] and intersecting the results. This approach also generalizes to all x86 vector types.
There are also the operations phadd.sw and phsub.sw, which perform saturating addition/subtraction. Use sadd_sat and ssub_sat to compute the KnownBits of these operations.
Also adjust the existing test case pr53247.ll because it can be transformed to a constant using the new KnownBits computation.
Fixes #82516.
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