[clang] [CIR] Split side_effect into memory effects, nounwind, and willreturn (PR #223890)

[Erich Keane via cfe-commits]

================
@@ -1986,39 +1986,74 @@ def CIR_BlockAddrDiffAttr
 }
 
 //===----------------------------------------------------------------------===//
-// Side Effect
+// Memory Effects
 //===----------------------------------------------------------------------===//
 
-def CIR_SideEffect : CIR_I32Enum<
-    "SideEffect", "allowed side effects of a function", [
-      I32EnumCase<"All", 0, "all">,
-      I32EnumCase<"Pure", 1, "pure">,
-      I32EnumCase<"Const", 2, "const">
+def CIR_ModRefInfo : CIR_I32Enum<
+    "ModRefInfo", "how a function accesses one class of memory", [
+      I32EnumCase<"NoModRef", 0, "none">,
+      I32EnumCase<"Ref", 1, "read">,
+      I32EnumCase<"Mod", 2, "write">,
+      I32EnumCase<"ModRef", 3, "readwrite">
 ]> {
   let description = [{
-    The side effect attribute specifies the possible side effects of a function
-    or the target of a call operation.  This is an enumeration attribute with
-    the following possible values:
-
-    - all: The function or callee can have any side effects. This is the default
-      if no side effects are explicitly listed.
-    - pure: The function or 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 function or callee may not read or write data from memory. This
-      has the same effect as the GNU C/C++ attribute `__attribute__((const))`.
+    Whether a function may read and/or write one class of memory.  The
----------------
erichkeane wrote:

The 2nd sentence of this description is not helpful at all, its explaining a tautology.  Also, 'which class'? And in what way? 

https://github.com/llvm/llvm-project/pull/223890