[PATCH] D64512: [InstCombine] Dropping redundant masking before left-shift [0/5] (PR42563)

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

I As discussed at http://lists.llvm.org/pipermail/llvm-dev/2017-March/111257.html, instcombine is probably doing too much work in general given the number of times it's run.  But I don't think this specific use of instsimplify here is likely to be a problem in practice; given the pattern guard, it should trigger very rarely.



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Comment at: llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp:96
+  Value *SumOfShAmts =
+      SimplifyBinOp(Instruction::BinaryOps::Add, MaskShAmt, ShiftShAmt,
+                    SQ.getWithInstruction(OuterShift));
----------------
SimplifyAddInst?


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