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

[Julius Alexandre via llvm-commits]

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@@ -1921,6 +1921,14 @@ def int_coro_subfn_addr : DefaultAttrsIntrinsic<
     [IntrReadMem, IntrArgMemOnly, ReadOnly<ArgIndex<0>>,
      NoCapture<ArgIndex<0>>]>;
 
+///===---------------------- Constant Time Intrinsics ----------------------===//
+//
+// Intrinsic to support constant time select
+def int_ct_select
+    : DefaultAttrsIntrinsic<[llvm_any_ty],
+                            [llvm_i1_ty, LLVMMatchType<0>, LLVMMatchType<0>],
+                            [IntrWriteMem, IntrWillReturn, NoUndef<RetIndex>]>;
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wizardengineer wrote:

Switched it to IntrInaccessibleMemOnly in 64613ed31ef6, so the call stays pinned without claiming to write accessible memory.

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