[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
+    spellings match LLVM's, so `none` means neither read nor written and
+    `readwrite` means both may happen.
+  }];
+}
 
-    Examples:
+def CIR_MemoryEffectsAttr : CIR_Attr<"MemoryEffects", "memory_effects"> {
+  let summary = "What memory a function or callee may touch";
+  let description = [{
+    The memory a function or the target of a call may read and write, given
----------------
erichkeane wrote:

There is a general 'wrong voice' to the first sentence here?  It is supposed to describe what 'memory effects attr' does, but doesn't really do that the same way other attributes are?  

Usually I'm not picky about this documentation, but it is completely different than the rest of our docs.

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