Add FatalIf utility to simplify some Fatal cases

src/support/utilities.h

diff --git a/src/support/utilities.h b/src/support/utilities.h
index a2fff7f..021d9d4 100644
--- a/src/support/utilities.h
+++ b/src/support/utilities.h
@@ -58,24 +58,46 @@
     return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
 }
 
-// For fatal errors which could arise from input (i.e. not assertion failures)
-class Fatal {
+// Helper for non-asserting failures.
+// Used to collapse code like:
+//   if (foo() && !bar()) {
+//     Fatal() << "Error: foo and not bar!";
+//   }
+// Into:
+//   FatalIf(foo() && !bar()) << "foo and not bar!";
+class FatalIf {
+  bool condition;
  public:
-  Fatal() {
-    std::cerr << "Fatal: ";
+  FatalIf(bool condition) : condition(condition) {
+    if (condition) {
+      std::cerr << "Fatal: ";
+    }
   }
   template<typename T>
-  Fatal &operator<<(T arg) {
-    std::cerr << arg;
+  FatalIf &operator<<(T arg) {
+    if (condition) {
+      std::cerr << arg;
+    }
     return *this;
   }
+  ~FatalIf() {
+    if (condition) {
+      std::cerr << "\n";
+      exit(1);
+    }
+  }
+};
+
+// For fatal errors which could arise from input (i.e. not assertion failures)
+class Fatal : public FatalIf {
+ public:
+  Fatal() : FatalIf(true) { }
   WASM_NORETURN ~Fatal() {
     std::cerr << "\n";
     exit(1);
   }
 };
 
-
 }  // namespace wasm
 
 #endif   // wasm_support_utilities_h

src/tools/asm2wasm.cpp

diff --git a/src/tools/asm2wasm.cpp b/src/tools/asm2wasm.cpp
index 1cf7947..aeca002 100644
--- a/src/tools/asm2wasm.cpp
+++ b/src/tools/asm2wasm.cpp
@@ -131,9 +131,8 @@
   }
 
   if (options.runningDefaultOptimizationPasses()) {
-    if (options.passes.size() > 1) {
-      Fatal() << "asm2wasm can only run default optimization passes (-O, -Ox, etc.), and not specific additional passes";
-    }
+    FatalIf(options.passes.size() > 1)
+      << "asm2wasm can only run default optimization passes (-O, -Ox, etc.), and not specific additional passes";
   }
 
   const auto &tm_it = options.extra.find("total memory");

src/tools/s2wasm.cpp

diff --git a/src/tools/s2wasm.cpp b/src/tools/s2wasm.cpp
index dc6b1f3..cc6a599 100644
--- a/src/tools/s2wasm.cpp
+++ b/src/tools/s2wasm.cpp
@@ -177,10 +177,9 @@
     emitBinary = false;
   }
 
-  if (allowMemoryGrowth && !generateEmscriptenGlue) {
-    Fatal() << "Error: adding memory growth code without Emscripten glue. "
-      "This doesn't do anything.\n";
-  }
+  FatalIf(allowMemoryGrowth && !generateEmscriptenGlue)
+    << "Error: adding memory growth code without Emscripten glue. "
+       "This doesn't do anything.\n";
 
   auto debugFlag = options.debug ? Flags::Debug : Flags::Release;
   auto input(read_file<std::string>(options.extra["infile"], Flags::Text, debugFlag));
@@ -221,7 +220,7 @@
     auto archiveFile(read_file<std::vector<char>>(m, Flags::Binary, debugFlag));
     bool error;
     Archive lib(archiveFile, error);
-    if (error) Fatal() << "Error opening archive " << m << "\n";
+    FatalIf(error) << "Error opening archive " << m << "\n";
     linker.linkArchive(lib);
   }
 

src/tools/wasm-emscripten-finalize.cpp

diff --git a/src/tools/wasm-emscripten-finalize.cpp b/src/tools/wasm-emscripten-finalize.cpp
index 7d00e81..85a3321 100644
--- a/src/tools/wasm-emscripten-finalize.cpp
+++ b/src/tools/wasm-emscripten-finalize.cpp
@@ -74,12 +74,8 @@
                       });
   options.parse(argc, argv);
 
-  if (infile == "") {
-    Fatal() << "Need to specify an infile\n";
-  }
-  if (outfile == "" && emitBinary) {
-    Fatal() << "Need to specify an outfile, or use text output\n";
-  }
+  FatalIf(infile == "") << "Need to specify an infile\n";
+  FatalIf(outfile == "" && emitBinary) << "Need to specify an outfile, or use text output\n";
 
   Module wasm;
   ModuleReader reader;
@@ -91,16 +87,10 @@
   }
 
   Export* dataEndExport = wasm.getExport("__data_end");
-  if (dataEndExport == nullptr) {
-    Fatal() << "__data_end export not found";
-  }
+  FatalIf(dataEndExport == nullptr) << "__data_end export not found";
   Global* dataEnd = wasm.getGlobal(dataEndExport->value);
-  if (dataEnd == nullptr) {
-    Fatal() << "__data_end global not found";
-  }
-  if (dataEnd->type != Type::i32) {
-    Fatal() << "__data_end global has wrong type";
-  }
+  FatalIf(dataEnd == nullptr) << "__data_end global not found";
+  FatalIf(dataEnd->type != Type::i32) << "__data_end global has wrong type";
   Const* dataEndConst = dataEnd->init->cast<Const>();
   uint32_t dataSize = dataEndConst->value.geti32() - globalBase;