[clang] [CIR] Add support for __builtin_expect (PR #144726)

[Sirui Mu via cfe-commits]

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@@ -2446,4 +2446,41 @@ def AssumeOp : CIR_Op<"assume"> {
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// Branch Probability Operations
+//===----------------------------------------------------------------------===//
+
+def ExpectOp : CIR_Op<"expect",
+  [Pure, AllTypesMatch<["result", "val", "expected"]>]> {
+  let summary = "Tell the optimizer that two values are likely to be equal.";
+  let description = [{
+    The `cir.expect` operation may take 2 or 3 arguments.
+
+    When the argument `prob` is missing, this operation effectively models the
+    `__builtin_expect` builtin function. It tells the optimizer that `val` and
+    `expected` are likely to be equal.
+
+    When the argumen `prob` is present, this operation effectively models the
+    `__builtin_expect_with_probability` builtin function. It tells the
+    optimizer that `val` and `expected` are equal to each other with a certain
+    probability.
+
+    `val` and `expected` must be integers and their types must match.
----------------
Lancern wrote:

The `@llvm.expect` intrinsic function accepts `i1`, `i32`, and `i64` as arguments. We may take it as a reference.

https://github.com/llvm/llvm-project/pull/144726