[PATCH] D108201: [AggressiveInstCombine] Add logical shift right instr to `TruncInstCombine` DAG

[Sanjay Patel via Phabricator via llvm-commits]

spatel added inline comments.


================
Comment at: llvm/lib/Transforms/AggressiveInstCombine/TruncInstCombine.cpp:297-298
+        KnownBits KnownLHS = computeKnownBits(I->getOperand(0), DL);
+        MinBitWidth =
+            std::max(MinBitWidth, KnownLHS.getMaxValue().getActiveBits());
+        if (MinBitWidth >= OrigBitWidth)
----------------
anton-afanasyev wrote:
> spatel wrote:
> > We already returned if MinBitWdith based on KnownRHS was too big, so this std::max is redundant?
> No, it isn't: we still use this updated MinBitWidth by setting it to instruction Info:
> ```
> Itr.second.MinBitWidth = MinBitWidth;
> ```
> This value is then used while computing common MinBitWidth in getMinBitWidth() function.
Ah, ok. Do we have a test to exercise that path? I didn't see any test failures when I made the change locally.


Repository:
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  https://reviews.llvm.org/D108201/new/

https://reviews.llvm.org/D108201