[clang] [CIR] Add side effect attribute to call operations (PR #144201)

[Andy Kaylor via cfe-commits]

================
@@ -1858,6 +1858,40 @@ def FuncOp : CIR_Op<"func", [
 // CallOp
 //===----------------------------------------------------------------------===//
 
+def SE_All : I32EnumAttrCase<"All", 1, "all">;
+def SE_Pure : I32EnumAttrCase<"Pure", 2, "pure">;
+def SE_Const : I32EnumAttrCase<"Const", 3, "const">;
+
+def SideEffect
+    : I32EnumAttr<
+          "SideEffect",
+          "allowed side effects of a function", [SE_All, SE_Pure, SE_Const]> {
+  let description = [{
+    The side effect attribute specifies the possible side effects of the callee
+    of a call operation. This is an enumeration attribute and all possible
+    enumerators are:
+
+    - all: The callee can have any side effects. This is the default if no side
+      effects are explicitly listed.
+    - pure: The callee may read data from memory, but it cannot write data to
----------------
andykaylor wrote:

Do we really want to model these using the GCC attribute names? I guess this is OK for now, but it seems like we might be better off with more general modeling that is consistent with the LLVM IR side effect handling (`memory(read)` = `pure` and `memory(none)` = `const`).

https://github.com/llvm/llvm-project/pull/144201