[mlir] Adds argument attributes for using LLVM's sret and byval attributes

to the conversion of LLVM IR dialect. These attributes are used in FIR to
support the lowering of Fortran using target-specific calling conventions.

Add roundtrip tests.

Add changes per review comments/concerns.

Reviewed By: ftynse

Differential Revision: https://reviews.llvm.org/D94052

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -1102,6 +1102,22 @@ LogicalResult ModuleTranslation::convertOneFunction(LLVMFuncOp func) {
           llvm::AttrBuilder().addAlignmentAttr(llvm::Align(attr.getInt())));
     }
 
+    if (auto attr = func.getArgAttrOfType<UnitAttr>(argIdx, "llvm.sret")) {
+      auto argTy = mlirArg.getType();
+      if (!argTy.isa<LLVM::LLVMPointerType>())
+        return func.emitError(
+            "llvm.sret attribute attached to LLVM non-pointer argument");
+      llvmArg.addAttr(llvm::Attribute::AttrKind::StructRet);
+    }
+
+    if (auto attr = func.getArgAttrOfType<UnitAttr>(argIdx, "llvm.byval")) {
+      auto argTy = mlirArg.getType();
+      if (!argTy.isa<LLVM::LLVMPointerType>())
+        return func.emitError(
+            "llvm.byval attribute attached to LLVM non-pointer argument");
+      llvmArg.addAttr(llvm::Attribute::AttrKind::ByVal);
+    }
+
     valueMapping[mlirArg] = &llvmArg;
     argIdx++;
   }

mlir/test/Dialect/LLVMIR/func.mlir

@@ -87,6 +87,16 @@ module {
     llvm.return
   }
 
+  // CHECK: llvm.func @byvalattr(%{{.*}}: !llvm.ptr<i32> {llvm.byval})
+  llvm.func @byvalattr(%arg0: !llvm.ptr<i32> {llvm.byval}) {
+    llvm.return
+  }
+
+  // CHECK: llvm.func @sretattr(%{{.*}}: !llvm.ptr<i32> {llvm.sret})
+  llvm.func @sretattr(%arg0: !llvm.ptr<i32> {llvm.sret}) {
+    llvm.return
+  }
+
   // CHECK: llvm.func @variadic(...)
   llvm.func @variadic(...)
 

mlir/test/Target/llvmir-invalid.mlir

@@ -14,6 +14,19 @@ llvm.func @invalid_noalias(%arg0 : !llvm.float {llvm.noalias = true}) -> !llvm.f
 
 // -----
 
+// expected-error @+1 {{llvm.sret attribute attached to LLVM non-pointer argument}}
+llvm.func @invalid_noalias(%arg0 : !llvm.float {llvm.sret}) -> !llvm.float {
+  llvm.return %arg0 : !llvm.float
+}
+// -----
+
+// expected-error @+1 {{llvm.byval attribute attached to LLVM non-pointer argument}}
+llvm.func @invalid_noalias(%arg0 : !llvm.float {llvm.byval}) -> !llvm.float {
+  llvm.return %arg0 : !llvm.float
+}
+
+// -----
+
 // expected-error @+1 {{llvm.align attribute attached to LLVM non-pointer argument}}
 llvm.func @invalid_align(%arg0 : !llvm.float {llvm.align = 4}) -> !llvm.float {
   llvm.return %arg0 : !llvm.float