[MLIR] Enable inlining for private symbols (#122572)

The inlining code for llvm funcs seems to have needlessly forbidden
inlining of private (e.g. non-cloning) symbols.

Author: wsmoses

mlir/lib/Dialect/LLVMIR/Transforms/InlinerInterfaceImpl.cpp

@@ -663,8 +663,6 @@ struct LLVMInlinerInterface : public DialectInlinerInterface {
 
   bool isLegalToInline(Operation *call, Operation *callable,
                        bool wouldBeCloned) const final {
-    if (!wouldBeCloned)
-      return false;
     if (!isa<LLVM::CallOp>(call)) {
       LLVM_DEBUG(llvm::dbgs() << "Cannot inline: call is not an '"
                               << LLVM::CallOp::getOperationName() << "' op\n");

mlir/test/Dialect/LLVMIR/inlining.mlir

@@ -663,3 +663,16 @@ llvm.func @caller() {
   llvm.call @vararg_intrinrics() : () -> ()
   llvm.return
 }
+
+// -----
+
+llvm.func @private_func(%a : i32) -> i32 attributes {sym_visibility = "private"} {
+  llvm.return %a : i32
+}
+
+// CHECK-LABEL: func @caller
+llvm.func @caller(%x : i32) -> i32 {
+  // CHECK-NOT: llvm.call @private_func
+  %z = llvm.call @private_func(%x) : (i32) -> (i32)
+  llvm.return %z : i32
+}