Emit MLIR trampoline wrapper function with LLVM private linkage

[mehdi_amini]

Summary

The wrapper, as most of compiler-generated functions, are intended to serve the
IR for the current module. The safest linkage is to keep these private to avoid
any possible collision with other modules.

[ingomueller-net]

You beat me to it ;)

I did this in parallel: https://reviews.llvm.org/D153256. My patch preserves any llvm.linkage flags on the original op, so the very last test behaves different. Not sure what is better...

[mehdi_amini]

We shouldn't preserve the original linkage, I'm not sure what to do with other attributes and why they are propagated actually.

[Dinistro]

LGTM!

mlir/lib/Conversion/FuncToLLVM/FuncToLLVM.cpp

filterFuncAttributes(
       attributes);
 
   // Create the auxiliary function.
   auto wrapperFunc = builder.create<LLVM::LLVMFuncOp>(
       loc, llvm::formatv("_mlir_ciface_{0}", funcOp.getName()).str(),
       wrapperType, LLVM::Linkage::External, /*dsoLocal*/ false,
       /*cconv*/ LLVM::CConv::C, attributes);
 
+  // The wrapper that we synthetize here should only be visible in this module.
+  newFuncOp.setLinkage(LLVM::Linkage::Private);
   builder.setInsertionPointToStart(newFuncOp.addEntryBlock());
 
   // Get a ValueRange containing arguments.
   FunctionType type = funcOp.getFunctionType();
   SmallVector<Value, 8> args;
   args.reserve(type.getNumInputs());
   ValueRange wrapperArgsRange(newFuncOp.getArguments());
 

mlir/test/Conversion/FuncToLLVM/emit-c-wrappers-for-external-functions.mlir

 // RUN: mlir-opt -llvm-request-c-wrappers -convert-func-to-llvm='use-opaque-pointers=1' %s | FileCheck %s
 
-// CHECK: llvm.func @res_attrs_with_memref_return() -> (!llvm.struct{{.*}} {test.returnOne})
+// CHECK: llvm.func private @res_attrs_with_memref_return() -> (!llvm.struct{{.*}} {test.returnOne})
 // CHECK-LABEL: llvm.func @_mlir_ciface_res_attrs_with_memref_return
 // CHECK-SAME: !llvm.ptr
 // CHECK-NOT: test.returnOne
 func.func private @res_attrs_with_memref_return() -> (memref<f32> {test.returnOne})
 
-// CHECK: llvm.func @res_attrs_with_value_return() -> (f32 {test.returnOne = 1 : i64})
+// CHECK: llvm.func private @res_attrs_with_value_return() -> (f32 {test.returnOne = 1 : i64})
 // CHECK-LABEL: llvm.func @_mlir_ciface_res_attrs_with_value_return
 // CHECK-SAME: -> (f32 {test.returnOne = 1 : i64})
 func.func private @res_attrs_with_value_return() -> (f32 {test.returnOne = 1})
 
-// CHECK: llvm.func @multiple_return() -> !llvm.struct<{{.*}}>
+// CHECK: llvm.func private @multiple_return() -> !llvm.struct<{{.*}}>
 // CHECK-LABEL: llvm.func @_mlir_ciface_multiple_return
 // CHECK-NOT: test.returnOne
 // CHECK-NOT: test.returnTwo
 // CHECK-NOT: test.returnThree
 func.func private @multiple_return() -> (memref<f32> {test.returnOne = 1}, f32 {test.returnTwo = 2, test.returnThree = 3})
 
-// CHECK: llvm.func @multiple_return_missing_res_attr() -> !llvm.struct<{{.*}}>
+// CHECK: llvm.func private @multiple_return_missing_res_attr() -> !llvm.struct<{{.*}}>
 // CHECK-LABEL: llvm.func @_mlir_ciface_multiple_return_missing_res_attr
 // CHECK-NOT: test.returnOne
 // CHECK-NOT: test.returnTwo
 // CHECK-NOT: test.returnThree
 func.func private @multiple_return_missing_res_attr() -> (memref<f32> {test.returnOne = 1}, i64, f32 {test.returnTwo = 2, test.returnThree = 3})
 
-// CHECK: llvm.func @one_arg_attr_no_res_attrs_with_memref_return({{.*}}) -> !llvm.struct{{.*}}
+// CHECK: llvm.func private @one_arg_attr_no_res_attrs_with_memref_return({{.*}}) -> !llvm.struct{{.*}}
 // CHECK-LABEL: llvm.func @_mlir_ciface_one_arg_attr_no_res_attrs_with_memref_return
 // CHECK-SAME: !llvm.ptr
 // CHECK-SAME: !llvm.ptr
 // CHECK-SAME: {test.argOne = 1 : i64})
 func.func private @one_arg_attr_no_res_attrs_with_memref_return(%arg0: memref<f32> {test.argOne = 1}) -> memref<f32>
 
-// CHECK: llvm.func @one_arg_attr_one_res_attr_with_memref_return({{.*}}) -> (!llvm.struct<{{.*}}> {test.returnOne = 1 : i64})
+// CHECK: llvm.func private @one_arg_attr_one_res_attr_with_memref_return({{.*}}) -> (!llvm.struct<{{.*}}> {test.returnOne = 1 : i64})
 // CHECK-LABEL: llvm.func @_mlir_ciface_one_arg_attr_one_res_attr_with_memref_return
 // CHECK-SAME: !llvm.ptr
 // CHECK-NOT: test.returnOne
 // CHECK-SAME: !llvm.ptr
 // CHECK-SAME: {test.argOne = 1 : i64})
 func.func private @one_arg_attr_one_res_attr_with_memref_return(%arg0: memref<f32> {test.argOne = 1}) -> (memref<f32> {test.returnOne = 1})
 
-// CHECK: llvm.func @one_arg_attr_one_res_attr_with_value_return({{.*}}) -> (f32 {test.returnOne = 1 : i64})
+// CHECK: llvm.func private @one_arg_attr_one_res_attr_with_value_return({{.*}}) -> (f32 {test.returnOne = 1 : i64})
 // CHECK-LABEL: llvm.func @_mlir_ciface_one_arg_attr_one_res_attr_with_value_return
 // CHECK-SAME: !llvm.ptr
 // CHECK-SAME: {test.argOne = 1 : i64}
 // CHECK-SAME: -> (f32 {test.returnOne = 1 : i64})
 func.func private @one_arg_attr_one_res_attr_with_value_return(%arg0: memref<f32> {test.argOne = 1}) -> (f32 {test.returnOne = 1})
 
-// CHECK: llvm.func @multiple_arg_attr_multiple_res_attr({{.*}}) -> !llvm.struct<{{.*}}>
+// CHECK: llvm.func private @multiple_arg_attr_multiple_res_attr({{.*}}) -> !llvm.struct<{{.*}}>
 // CHECK-LABEL: llvm.func @_mlir_ciface_multiple_arg_attr_multiple_res_attr
 // CHECK-SAME: !llvm.ptr
 // CHECK-NOT: test.returnOne
 // CHECK-NOT: test.returnTwo
 // CHECK-SAME: !llvm.ptr
 // CHECK-SAME: {test.argZero = 0 : i64}
 // CHECK-SAME: f32
 // CHECK-SAME: i32 {test.argTwo = 2 : i64})
 func.func private @multiple_arg_attr_multiple_res_attr(%arg0: memref<f32> {test.argZero = 0}, %arg1: f32, %arg2: i32 {test.argTwo = 2}) -> (f32, memref<i32> {test.returnOne = 1}, i32 {test.returnTwo = 2})
 
-// CHECK: llvm.func weak @drop_linkage_attr() -> (!llvm.struct{{.*}} {test.returnOne})
+// CHECK: llvm.func private @drop_linkage_attr() -> (!llvm.struct{{.*}} {test.returnOne})
 // CHECK-LABEL: llvm.func @_mlir_ciface_drop_linkage_attr
 // CHECK-SAME: !llvm.ptr
 // CHECK-NOT: llvm.linkage
 func.func private @drop_linkage_attr() -> (memref<f32> {test.returnOne}) attributes { llvm.linkage = #llvm.linkage<weak> }