[clang] [CIR] Match OGCG noalias and memory effects on operator new (PR #221818)

[Andy Kaylor via cfe-commits]

================
@@ -457,6 +457,18 @@ void convertSideEffectForCall(mlir::Operation *callOp, bool isNothrow,
     noUnwind = true;
     willReturn = true;
     break;
+
+  case cir::SideEffect::InaccessibleOrErrno:
+    memoryEffect = mlir::LLVM::MemoryEffectsAttr::get(
+        callOp->getContext(), /*other=*/ModRefInfo::NoModRef,
+        /*argMem=*/ModRefInfo::NoModRef,
+        /*inaccessibleMem=*/ModRefInfo::ModRef,
+        /*errnoMem=*/ModRefInfo::Mod,
----------------
andykaylor wrote:

The assumption of `ModRefInfo::Mod` here is problematic. That's the only way classic codegen ever uses `llvm::MemoryEffects::inaccessibleOrErrnoMemOnly()` but the function allows other combinations.

https://github.com/llvm/llvm-project/pull/221818