[PATCH] D103153: [InstCombine] Add fold for extracting known elements from a stepvector

[Caroline via Phabricator via llvm-commits]

CarolineConcatto marked 2 inline comments as done.
CarolineConcatto added inline comments.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp:361
+        // vector to truncate the index safely.
+        if (IndexC->getValue().getActiveBits() <= (BitWidth - 1)) {
+          auto *Idx =
----------------
foad wrote:
> All these quantities are unsigned so there is no need to subtract 1 for the sign bit.
LLVM-IR always surprising me.
I was surprised when the test replaced 255 by -1. 
But if llvm-ir does not reserve 1 bit for  sign I accept that -1 is equal to 255.




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  https://reviews.llvm.org/D103153/new/

https://reviews.llvm.org/D103153