[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:

I didn't necessarily mean to say I wanted to change this in order to be consistent with the LLVM IR representation. I just think that's a better, more general representation. To me `pure` and `const` are unclear, particularly given that both terms have conflicting meanings in C++.

Do we represent side-effects on LLVM intrinsic calls? Those would require a richer representation. It would also be nice to mark things like whether a function modifies `errno` or whether it depends on or modifies the floating-point environment.

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