[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
+      memory. This has the same effect as the GNU C/C++ attribute
+      `__attribute__((pure))`.
+    - const: The callee may not read or write data from memory. This has the
+      same effect as the GNU C/C++ attribute `__attribute__((const))`.
+
+    Examples:
+
+    ```mlir
+    %0 = cir.const #cir.int<0> : !s32i
+    %1 = cir.const #cir.int<1> : !s32i
+    %2 = cir.call @add(%0, %1) : (!s32i, !s32i) -> !s32i side_effect(all)
----------------
andykaylor wrote:

```suggestion
    %2 = cir.call @add(%0, %1) : (!s32i, !s32i) -> !s32i
```
`side_effect(all)` doesn't get printed

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