[clang] [CIR] Widen const/pure side effects for ABI argument memory (PR #221067)

[Andy Kaylor via cfe-commits]

================
@@ -420,45 +420,53 @@ mlir::Value lowerCirAttrAsValue(mlir::Operation *parentOp,
   return value;
 }
 
-void convertSideEffectForCall(mlir::Operation *callOp, bool isNothrow,
-                              cir::SideEffect sideEffect,
-                              mlir::LLVM::MemoryEffectsAttr &memoryEffect,
-                              bool &noUnwind, bool &willReturn,
-                              bool &noReturn) {
+/// Lower a CIR `side_effect` to an LLVM memory effect.  A null result means
+/// unknown effects, which is how `All` is represented.  The argmem values
+/// lower to ModRef because they do not say whether the slot is read or
+/// written.
+static mlir::LLVM::MemoryEffectsAttr
+buildMemoryEffects(mlir::MLIRContext *ctx, cir::SideEffect sideEffect) {
   using mlir::LLVM::ModRefInfo;
 
+  ModRefInfo other;
+  ModRefInfo argMem;
   switch (sideEffect) {
   case cir::SideEffect::All:
-    memoryEffect = {};
-    noUnwind = isNothrow;
-    willReturn = false;
-    break;
-
+    return {};
   case cir::SideEffect::Pure:
-    memoryEffect = mlir::LLVM::MemoryEffectsAttr::get(
-        callOp->getContext(), /*other=*/ModRefInfo::Ref,
-        /*argMem=*/ModRefInfo::Ref,
-        /*inaccessibleMem=*/ModRefInfo::Ref,
-        /*errnoMem=*/ModRefInfo::Ref,
-        /*targetMem0=*/ModRefInfo::Ref,
-        /*targetMem1=*/ModRefInfo::Ref);
-    noUnwind = true;
-    willReturn = true;
+    other = argMem = ModRefInfo::Ref;
     break;
-
   case cir::SideEffect::Const:
-    memoryEffect = mlir::LLVM::MemoryEffectsAttr::get(
-        callOp->getContext(), /*other=*/ModRefInfo::NoModRef,
-        /*argMem=*/ModRefInfo::NoModRef,
-        /*inaccessibleMem=*/ModRefInfo::NoModRef,
-        /*errnoMem=*/ModRefInfo::NoModRef,
-        /*targetMem0=*/ModRefInfo::NoModRef,
-        /*targetMem1=*/ModRefInfo::NoModRef);
-    noUnwind = true;
-    willReturn = true;
+    other = argMem = ModRefInfo::NoModRef;
+    break;
+  case cir::SideEffect::PureArgMem:
----------------
andykaylor wrote:

I don't understand what "PureArgMem" means. "Pure" and "argmem: modref" are contradictory.

https://github.com/llvm/llvm-project/pull/221067