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

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp:299-307
+      if (I->getOpcode() == Instruction::AShr ||
+          I->getOpcode() == Instruction::LShr) {
         KnownBits KnownLHS = computeKnownBits(I->getOperand(0), DL);
         MinBitWidth =
-            std::max(MinBitWidth, KnownLHS.getMaxValue().getActiveBits());
+            std::max(MinBitWidth, OrigBitWidth - KnownLHS.countMinSignBits() +
+                                      KnownLHS.isNegative());
         if (MinBitWidth >= OrigBitWidth)
----------------



Repository:
  rG LLVM Github Monorepo

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

https://reviews.llvm.org/D108355