[PATCH] D108355: [AggressiveInstCombine] Add arithmetic shift right instr to `TruncInstCombine` DAG

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


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Comment at: llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp:295-297
+                                 .uadd_sat(APInt(OrigBitWidth, 1))
+                                 .getLimitedValue(OrigBitWidth);
+      if (MinBitWidth == OrigBitWidth)
----------------
These seem like a separate change


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Comment at: llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp:409-410
+      Value *RHS = getReducedOperand(I->getOperand(1), SclTy);
+      KnownBits KnownLHS = computeKnownBits(I->getOperand(0), DL);
+      Opc = KnownLHS.isNegative() ? Instruction::AShr : Instruction::LShr;
       // Preserve `exact` flag since truncation doesn't change exactness
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[Why] do we have to do this?
Doesn't seem like something this transform should worry about?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D108355/new/

https://reviews.llvm.org/D108355