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

[Simon Tatham via llvm-commits]

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@@ -476,8 +480,8 @@ class LLVM_ABI TargetLoweringBase {
   MachineMemOperand::Flags
   getVPIntrinsicMemOperandFlags(const VPIntrinsic &VPIntrin) const;
 
-  virtual bool isSelectSupported(SelectSupportKind /*kind*/) const {
-    return true;
+  virtual bool isSelectSupported(SelectSupportKind kind) const {
+    return kind != CtSelect;
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statham-arm wrote:

Why is this not checking for all three of the new values you added? It looks as if will assume by default that every target supports `ScalarCondVectorValCtSelect` and `VectorMaskValCtSelect`.

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