[PATCH] D84664: [InstCombine] Fold shift-select if all the operands are constant

[Matteo Favaro via Phabricator via llvm-commits]

fvrmatteo added a comment.

I thought the same when I first saw those calls to **hasOneUse**, but if the code to handle the multiple users case that I added to **InstructionCombining.cpp** is kept and the calls to **SimplifySelectsFeedingBinaryOp** are removed from **InstCombineShifts.cpp**, the simplification won't work anymore.

In the example @nikic just shared, the single use-case it's handled by **commonShiftTransforms** -> **FoldShiftByConstant** (and not by **SimplifySelectsFeedingBinaryOp**, which is never called for the shifts, even though it would be correct to do so, I think),  but that doesn't seem to handle in a meaningful way the case where the incoming value to the shift it's use more than once.


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https://reviews.llvm.org/D84664