Add wasm-opt warning

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -826,4 +826,12 @@ def err_drv_triple_version_invalid : Error<
 
 def warn_missing_include_dirs : Warning<
   "no such include directory: '%0'">, InGroup<MissingIncludeDirs>, DefaultIgnore;
+
+def warn_wasm_opt_not_found : Warning<
+  "wasm-opt was not found, some optimizations were not applied">,
+  InGroup<WebAssemblyOptimization>;
+def err_wasm_opt_not_found_with_flag : Error<
+  "wasm-opt was explicitly requested, but was not found">;
+def err_wasm_opt_requested_but_not_supported : Error<
+  "wasm-opt was explicitly requested, but is not supported with '%0'">;
 }

clang/include/clang/Basic/DiagnosticGroups.td

@@ -1520,6 +1520,8 @@ in addition with the pragmas or -fmax-tokens flag to get any warnings.
 
 def WebAssemblyExceptionSpec : DiagGroup<"wasm-exception-spec">;
 
+def WebAssemblyOptimization : DiagGroup<"wasm-opt">;
+
 def RTTI : DiagGroup<"rtti">;
 
 def OpenCLCoreFeaturesDiagGroup : DiagGroup<"pedantic-core-features">;

clang/include/clang/Driver/Options.td

@@ -8923,3 +8923,4 @@ def wasm_opt : Flag<["--"], "wasm-opt">,
   Group<m_Group>,
   HelpText<"Enable the wasm-opt optimizer (default)">,
   MarshallingInfoNegativeFlag<LangOpts<"NoWasmOpt">>;
+def Wwarn_wasm_opt_not_found : Flag<["-"], "Wwarn_wasm_opt_not_found">;

clang/lib/Driver/ToolChains/WebAssembly.cpp

@@ -9,6 +9,7 @@
 #include "WebAssembly.h"
 #include "CommonArgs.h"
 #include "Gnu.h"
+#include "clang/Basic/DiagnosticDriver.h"
 #include "clang/Basic/Version.h"
 #include "clang/Config/config.h"
 #include "clang/Driver/Compilation.h"
@@ -20,6 +21,7 @@
 #include "llvm/Support/Path.h"
 #include "llvm/Support/VirtualFileSystem.h"
 
+
 using namespace clang::driver;
 using namespace clang::driver::tools;
 using namespace clang::driver::toolchains;
@@ -172,6 +174,11 @@ void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   bool RunWasmOpt = Args.hasFlag(options::OPT_wasm_opt,
                                  options::OPT_no_wasm_opt, WasmOptDefault);
 
+  if (TargetBuildsComponents(ToolChain.getTriple()) &&
+      Args.hasFlag(options::OPT_wasm_opt, options::OPT_no_wasm_opt, false)) {
+    ToolChain.getDriver().Diag(diag::err_wasm_opt_requested_but_not_supported)
+        << ToolChain.getTriple().str();
+  }
   // If wasm-opt is enabled and optimizations are happening look for the
   // `wasm-opt` program. If it's not found auto-disable it.
   std::string WasmOptPath;
@@ -180,6 +187,14 @@ void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
     if (WasmOptPath == "wasm-opt") {
       WasmOptPath = {};
     }
+    if (WasmOptPath.empty()) {
+      if (Args.hasFlag(options::OPT_wasm_opt, options::OPT_no_wasm_opt,
+                       false)) {
+        ToolChain.getDriver().Diag(diag::err_wasm_opt_not_found_with_flag);
+      } else {
+        ToolChain.getDriver().Diag(diag::warn_wasm_opt_not_found);
+      }
+    }
   }
 
   if (!WasmOptPath.empty()) {