[llvm] [ConstantTime][LLVM] Add llvm.ct.select intrinsic with generic SelectionDAG lowering (PR #166702)

[Julius Alexandre via llvm-commits]

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@@ -783,6 +783,10 @@ enum NodeType {
   /// i1 then the high bits must conform to getBooleanContents.
   SELECT,
 
+  /// Constant-time Select, implemented with CMOV instruction. This is used to
+  /// implement constant-time select.
+  CTSELECT,
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wizardengineer wrote:

> implemented with CMOV instruction ? Your description says these will be expanded to bitselect patterns?

Good catch, that's not suppose to be there. Original when we were constructing the constant-time code, we had added implementation for the specific archs (like x86 in this case), the fallback implementation was added later. So I think that's why the comment mentions CMOV. I'll make sure to fix it, thanks! :)

https://github.com/llvm/llvm-project/pull/166702