Index: flang/tools/f18/f18.cpp
===================================================================
--- flang/tools/f18/f18.cpp
+++ flang/tools/f18/f18.cpp
@@ -109,6 +109,8 @@
   bool getDefinition{false};
   GetDefinitionArgs getDefinitionArgs{0, 0, 0};
   bool getSymbolsSources{false};
+  bool dashc{true};
+  bool assemble{true};
 };
 
 void Exec(std::vector<llvm::StringRef> &argv, bool verbose = false) {
@@ -135,10 +137,15 @@
   for (size_t j{0}; j < driver.F18_FCArgs.size(); ++j) {
     argv.push_back(driver.F18_FCArgs[j]);
   }
-  char dashC[3] = "-c", dashO[3] = "-o";
-  argv.push_back(dashC);
+  char dashC[3] = "-c", dashO[3] = "-o", dashS[3] = "-S";
+  if (driver.dashc) {
+    argv.push_back(dashC);
+  }
   argv.push_back(dashO);
   argv.push_back(relo);
+  if (!driver.assemble) {
+    argv.push_back(dashS);
+  }
   argv.push_back(source);
   Exec(argv, driver.verbose);
 }
@@ -157,7 +164,11 @@
   if (dot != std::string::npos) {
     relo = base.substr(0, dot);
   }
-  relo += ".o";
+  if (driver.assemble) {
+    relo += ".o";
+  } else {
+    relo += ".s";
+  }
   return relo;
 }
 
@@ -617,7 +628,8 @@
           << "\n"
           << "Defaults:\n"
           << "  When invoked with input files, and no options to tell\n"
-          << "  it otherwise, f18 will unparse its input and pass that on to an\n"
+          << "  it otherwise, f18 will unparse its input and pass that on to "
+             "an\n"
           << "  external compiler to continue the compilation.\n"
           << "  The external compiler is specified by the F18_FC environment\n"
           << "  variable. The default is 'gfortran'.\n"
@@ -655,13 +667,18 @@
           << "  -fdebug-no-semantics  disable semantic checks\n"
           << "  -fget-definition\n"
           << "  -fget-symbols-sources\n"
-          << "  -v -c -o -I -D -U    have their usual meanings\n"
+          << "  -v -c -o -I -D -U -S   have their usual meanings\n"
           << "  -help                print this again\n"
-          << "Unrecognised options are passed through to the external compiler\n"
+          << "Unrecognised options are passed through to the external "
+             "compiler\n"
           << "set by F18_FC (see defaults).\n";
       return exitStatus;
     } else if (arg == "-V" || arg == "--version") {
       return printVersion();
+    } else if (arg == "-S") {
+      driver.dashc = false;
+      driver.assemble = false;
+      driver.compileOnly = true;
     } else {
       driver.F18_FCArgs.push_back(arg);
       if (arg == "-v") {