Support external wasm-ld linker for WebAssembly targets

Overridable with `-linker`.

.circleci/config.yml

@@ -129,7 +129,10 @@ commonSteps: &commonSteps
     - run:
         name: Run LIT testsuite
         when: always
-        command: cd ../ninja-ldc && ctest -V -R lit-tests
+        command: |
+          cd ../ninja-ldc
+          # Temporarily add LLVM bin dir to PATH, so that e.g. wasm-ld is found.
+          PATH=$PWD/../llvm-$LLVM_VERSION/bin:$PATH ctest -V -R lit-tests
     - run:
         name: Run DMD testsuite
         when: always

driver/linker-gcc.cpp

@@ -703,16 +703,28 @@ int linkObjToBinaryGcc(llvm::StringRef outputPath,
   }
 #endif
 
-  // find gcc for linking
+  // build command-line for gcc-compatible linker driver
-  const std::string tool = getGcc();
+  // exception: invoke (ld-compatible) linker directly for WebAssembly targets
+  std::string tool;
+  std::unique_ptr<ArgsBuilder> argsBuilder;
+#if LDC_LLVM_VER >= 500
+  if (global.params.targetTriple->isOSBinFormatWasm()) {
+    tool = getProgram("wasm-ld", &opts::linker);
+    argsBuilder = llvm::make_unique<LdArgsBuilder>();
+  } else {
+#endif
+    tool = getGcc();
+    argsBuilder = llvm::make_unique<ArgsBuilder>();
+#if LDC_LLVM_VER >= 500
+  }
+#endif
 
   // build arguments
-  ArgsBuilder argsBuilder;
+  argsBuilder->build(outputPath, defaultLibNames);
-  argsBuilder.build(outputPath, defaultLibNames);
 
   Logger::println("Linking with: ");
   Stream logstr = Logger::cout();
-  for (const auto &arg : argsBuilder.args) {
+  for (const auto &arg : argsBuilder->args) {
     if (!arg.empty()) {
       logstr << "'" << arg << "' ";
     }
@@ -720,5 +732,5 @@ int linkObjToBinaryGcc(llvm::StringRef outputPath,
   logstr << "\n"; // FIXME where's flush ?
 
   // try to call linker
-  return executeToolAndWait(tool, argsBuilder.args, global.params.verbose);
+  return executeToolAndWait(tool, argsBuilder->args, global.params.verbose);
 }

shippable.yml

@@ -89,7 +89,7 @@ build:
     # Build and run LDC D unittests
     - ctest --output-on-failure -R ldc2-unittest
     # Run LIT testsuite, ignore the errors
-    - ctest -V -R lit-tests || true
+    - PATH=$PWD/../llvm/bin:$PATH ctest -V -R lit-tests || true
     # Run DMD testsuite (non-debug only for now), ignore the errors
     - DMD_TESTSUITE_MAKE_ARGS='-j16 -k' ctest -V -R dmd-testsuite -E "-debug$" || true
     # Run druntime/Phobos unittests (non-debug only for now, excl. hanging core.thread), ignore the errors

tests/baremetal/wasm.d

@@ -1,7 +1,7 @@
 // Compile and link directly to WebAssembly.
 
 // REQUIRES: target_WebAssembly
-// RUN: %ldc -mtriple=wasm32-unknown-unknown-wasm -link-internally %s %baremetal_args
+// RUN: %ldc -mtriple=wasm32-unknown-unknown-wasm %s %baremetal_args
 
 extern(C): // no mangling, no arguments order reversal