Introduce -fmodules-ignore-macro=NNN to ignore a macro when building/loading modules.

The use of this flag enables a modules optimization where a given set
of macros can be labeled as "ignored" by the modules
system. Definitions of those macros will be completely ignored when
building the module hash and will be stripped when actually building
modules. The overall effect is that this flag can be used to
drastically reduce the number of

Eventually, we'll want modules to tell us what set of macros they
respond to (the "configuration macros"), and anything not in that set
will be excluded. However, that requires a lot of per-module
information that must be accurate, whereas this option can be used
more readily.

Fixes the rest of <rdar://problem/13165109>.

llvm-svn: 174560

1 files changed, 30 insertions, 0 deletions

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index b6115ec6ffa..356bf3171cc 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -743,6 +743,28 @@ static void doCompileMapModule(void *UserData) {
   Data.Instance.ExecuteAction(Data.CreateModuleAction);
 }
 
+namespace {
+  /// \brief Function object that checks with the given macro definition should
+  /// be removed, because it is one of the ignored macros.
+  class RemoveIgnoredMacro {
+    const HeaderSearchOptions &HSOpts;
+
+  public:
+    explicit RemoveIgnoredMacro(const HeaderSearchOptions &HSOpts)
+      : HSOpts(HSOpts) { }
+
+    bool operator()(const std::pair<std::string, bool> &def) const {
+      // Dig out the macro name.
+      StringRef MacroName = def.first;
+      StringRef::size_type EqPos = MacroName.find('=');
+      if (EqPos != StringRef::npos)
+        MacroName = MacroName.substr(0, EqPos);
+
+      return HSOpts.ModulesIgnoreMacros.count(MacroName) > 0;
+    }
+  };
+}
+
 /// \brief Compile a module file for the given module, using the options 
 /// provided by the importing compiler instance.
 static void compileModule(CompilerInstance &ImportingInstance,
@@ -779,6 +801,14 @@ static void compileModule(CompilerInstance &ImportingInstance,
   Invocation->getLangOpts()->resetNonModularOptions();
   PPOpts.resetNonModularOptions();
 
+  // Remove any macro definitions that are explicitly ignored by the module.
+  // They aren't supposed to affect how the module is built anyway.
+  const HeaderSearchOptions &HSOpts = Invocation->getHeaderSearchOpts();
+  PPOpts.Macros.erase(std::remove_if(PPOpts.Macros.begin(), PPOpts.Macros.end(),
+                                     RemoveIgnoredMacro(HSOpts)),
+                      PPOpts.Macros.end());
+
+
   // Note the name of the module we're building.
   Invocation->getLangOpts()->CurrentModule = Module->getTopLevelModuleName();