[PATCH] D71952: [X86][InstCombine] Add constant folding and simplification support for pdep and pext

[Craig Topper via Phabricator via llvm-commits]

craig.topper marked an inline comment as done.
craig.topper added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp:2522
+
+        while (Mask) {
+          // Isolate lowest set bit.
----------------
RKSimon wrote:
> Can you confirm this is correct? It doesn't seem to match:
> 
> https://www.felixcloutier.com/x86/pdep
> https://www.chessprogramming.org/BMI2#PDEP
> 
> But it might just be that my brain is still in a Christmas blur......
I think its right.  BitToTest here is equivalent to "bb" from the chessprogramming page. BitToSet is the mask & -mask. I reused it clear the bit in Mask where they used mask &= mask - 1.


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https://reviews.llvm.org/D71952