Add -MMD option

main.c

@@ -12,6 +12,7 @@ static StringArray opt_include;
 static bool opt_E;
 static bool opt_M;
 static bool opt_MD;
+static bool opt_MMD;
 static bool opt_MP;
 static bool opt_S;
 static bool opt_c;
@@ -22,6 +23,7 @@ static char *opt_MT;
 static char *opt_o;
 
 static StringArray ld_extra_args;
+static StringArray std_include_paths;
 
 char *base_file;
 static char *output_file;
@@ -52,6 +54,10 @@ static void add_default_include_paths(char *argv0) {
   strarray_push(&include_paths, "/usr/local/include");
   strarray_push(&include_paths, "/usr/include/x86_64-linux-gnu");
   strarray_push(&include_paths, "/usr/include");
+
+  // Keep a copy of the standard include paths for -MMD option.
+  for (int i = 0; i < include_paths.len; i++)
+    strarray_push(&std_include_paths, include_paths.data[i]);
 }
 
 static void define(char *str) {
@@ -245,6 +251,11 @@ static void parse_args(int argc, char **argv) {
       continue;
     }
 
+    if (!strcmp(argv[i], "-MMD")) {
+      opt_MD = opt_MMD = true;
+      continue;
+    }
+
     if (!strcmp(argv[i], "-cc1-input")) {
       base_file = argv[++i];
       continue;
@@ -395,6 +406,16 @@ static void print_tokens(Token *tok) {
   fprintf(out, "\n");
 }
 
+static bool in_std_include_path(char *path) {
+  for (int i = 0; i < std_include_paths.len; i++) {
+    char *dir = std_include_paths.data[i];
+    int len = strlen(dir);
+    if (strncmp(dir, path, len) == 0 && path[len] == '/')
+      return true;
+  }
+  return false;
+}
+
 // If -M options is given, the compiler write a list of input files to
 // stdout in a format that "make" command can read. This feature is
 // used to automate file dependency management.
@@ -417,13 +438,21 @@ static void print_dependencies(void) {
 
   File **files = get_input_files();
 
-  for (int i = 0; files[i]; i++)
+  for (int i = 0; files[i]; i++) {
+    if (opt_MMD && in_std_include_path(files[i]->name))
+      continue;
     fprintf(out, " \\\n  %s", files[i]->name);
+  }
+
   fprintf(out, "\n\n");
 
-  if (opt_MP)
-    for (int i = 1; files[i]; i++)
+  if (opt_MP) {
+    for (int i = 1; files[i]; i++) {
+      if (opt_MMD && in_std_include_path(files[i]->name))
+        continue;
       fprintf(out, "%s:\n\n", quote_makefile(files[i]->name));
+    }
+  }
 }
 
 static Token *must_tokenize_file(char *path) {