[WebAssembly] Add an import_field function attribute

This is similar to import_module, but sets the import field name
instead.

By default, the import field name is the same as the C/asm/.o symbol
name. However, there are situations where it's useful to have it be
different. For example, suppose I have a wasm API with a module named
"pwsix" and a field named "read". There's no risk of namespace
collisions with user code at the wasm level because the generic name
"read" is qualified by the module name "pwsix". However in the C/asm/.o
namespaces, the module name is not used, so if I have a global function
named "read", it is intruding on the user's namespace.

With the import_field module, I can declare my function (in libc) to be
"__read", and then set the wasm import module to be "pwsix" and the wasm
import field to be "read". So at the C/asm/.o levels, my symbol is
outside the user namespace.

Differential Revision: https://reviews.llvm.org/D57602

llvm-svn: 352930

clang/include/clang/Basic/Attr.td

@@ -1514,11 +1514,19 @@ def AMDGPUNumVGPR : InheritableAttr {
 def WebAssemblyImportModule : InheritableAttr,
                               TargetSpecificAttr<TargetWebAssembly> {
   let Spellings = [Clang<"import_module">];
-  let Args = [StringArgument<"ImportModuleName">];
+  let Args = [StringArgument<"ImportModule">];
   let Documentation = [WebAssemblyImportModuleDocs];
   let Subjects = SubjectList<[Function], ErrorDiag>;
 }
 
+def WebAssemblyImportName : InheritableAttr,
+                            TargetSpecificAttr<TargetWebAssembly> {
+  let Spellings = [Clang<"import_name">];
+  let Args = [StringArgument<"ImportName">];
+  let Documentation = [WebAssemblyImportNameDocs];
+  let Subjects = SubjectList<[Function], ErrorDiag>;
+}
+
 def NoSplitStack : InheritableAttr {
   let Spellings = [GCC<"no_split_stack">];
   let Subjects = SubjectList<[Function], ErrorDiag>;

clang/include/clang/Basic/AttrDocs.td

@@ -3730,6 +3730,23 @@ reuqest a specific module name be used instead.
   }];
 }
 
+def WebAssemblyImportNameDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Clang supports the ``__attribute__((import_name(<name>)))`` 
+attribute for the WebAssembly target. This attribute may be attached to a
+function declaration, where it modifies how the symbol is to be imported
+within the WebAssembly linking environment.
+
+WebAssembly imports use a two-level namespace scheme, consisting of a module
+name, which typically identifies a module from which to import, and a field
+name, which typically identifies a field from that module to import. By
+default, field names for C/C++ symbols are the same as their C/C++ symbol
+names. This attribute can be used to override the default behavior, and
+reuqest a specific field name be used instead.
+  }];
+}
+
 def ArtificialDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{

clang/lib/CodeGen/TargetInfo.cpp

@@ -765,7 +765,13 @@ public:
       if (const auto *Attr = FD->getAttr<WebAssemblyImportModuleAttr>()) {
         llvm::Function *Fn = cast<llvm::Function>(GV);
         llvm::AttrBuilder B;
-        B.addAttribute("wasm-import-module", Attr->getImportModuleName());
+        B.addAttribute("wasm-import-module", Attr->getImportModule());
+        Fn->addAttributes(llvm::AttributeList::FunctionIndex, B);
+      }
+      if (const auto *Attr = FD->getAttr<WebAssemblyImportNameAttr>()) {
+        llvm::Function *Fn = cast<llvm::Function>(GV);
+        llvm::AttrBuilder B;
+        B.addAttribute("wasm-import-name", Attr->getImportName());
         Fn->addAttributes(llvm::AttributeList::FunctionIndex, B);
       }
     }

clang/lib/Sema/SemaDeclAttr.cpp

@@ -5732,6 +5732,29 @@ static void handleWebAssemblyImportModuleAttr(Sema &S, Decl *D, const ParsedAttr
       AL.getAttributeSpellingListIndex()));
 }
 
+static void handleWebAssemblyImportNameAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  if (!isFunctionOrMethod(D)) {
+    S.Diag(D->getLocation(), diag::warn_attribute_wrong_decl_type)
+        << "'import_name'" << ExpectedFunction;
+    return;
+  }
+
+  auto *FD = cast<FunctionDecl>(D);
+  if (FD->isThisDeclarationADefinition()) {
+    S.Diag(D->getLocation(), diag::err_alias_is_definition) << FD << 0;
+    return;
+  }
+
+  StringRef Str;
+  SourceLocation ArgLoc;
+  if (!S.checkStringLiteralArgumentAttr(AL, 0, Str, &ArgLoc))
+    return;
+
+  FD->addAttr(::new (S.Context) WebAssemblyImportNameAttr(
+      AL.getRange(), S.Context, Str,
+      AL.getAttributeSpellingListIndex()));
+}
+
 static void handleRISCVInterruptAttr(Sema &S, Decl *D,
                                      const ParsedAttr &AL) {
   // Warn about repeated attributes.
@@ -6489,6 +6512,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_WebAssemblyImportModule:
     handleWebAssemblyImportModuleAttr(S, D, AL);
     break;
+  case ParsedAttr::AT_WebAssemblyImportName:
+    handleWebAssemblyImportNameAttr(S, D, AL);
+    break;
   case ParsedAttr::AT_IBAction:
     handleSimpleAttribute<IBActionAttr>(S, D, AL);
     break;

clang/test/CodeGen/wasm-import-name.c

@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -triple wasm32-unknown-unknown-wasm -emit-llvm -o - %s | FileCheck %s
+
+void __attribute__((import_name("bar"))) foo(void);
+
+void call(void) {
+  foo();
+}
+
+// CHECK: declare void @foo() [[A:#[0-9]+]]
+
+// CHECK: attributes [[A]] = {{{.*}} "wasm-import-name"="bar" {{.*}}}

clang/test/Misc/pragma-attribute-supported-attributes-list.test

@@ -138,6 +138,7 @@
 // CHECK-NEXT: WarnUnusedResult (SubjectMatchRule_objc_method, SubjectMatchRule_enum, SubjectMatchRule_record, SubjectMatchRule_hasType_functionType)
 // CHECK-NEXT: Weak (SubjectMatchRule_variable, SubjectMatchRule_function, SubjectMatchRule_record)
 // CHECK-NEXT: WeakRef (SubjectMatchRule_variable, SubjectMatchRule_function)
+// CHECK-NEXT: WebAssemblyImportName (SubjectMatchRule_function)
 // CHECK-NEXT: WebAssemblyImportModule (SubjectMatchRule_function)
 // CHECK-NEXT: WorkGroupSizeHint (SubjectMatchRule_function)
 // CHECK-NEXT: XRayInstrument (SubjectMatchRule_function, SubjectMatchRule_objc_method)