[PATCH] D69585: PerformPendingInstatiations() already in the PCH

[Luboš Luňák via Phabricator via cfe-commits]

llunak updated this revision to Diff 229722.
llunak added a comment.

It turns out that this patch may introduce unwanted changes, specifically it can cause err_specialization_after_instantiation if the specialization is done in a source file but needed already by code in the PCH. But this seems to be rare (I've encountered it only after building the Skia library with put-everything-in-the-PCH), is easy to avoid (PCHs often need little tweaks anyway) and the performance gain is very much worth it.

Still, this means there should be an option to enable this. Done in this version of the patch. I don't know how to handle tests for it, pretty much all the tests pass as said above, but it seems a bit silly to duplicate all the PCH-related ones to also use the flag.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D69585/new/

https://reviews.llvm.org/D69585

Files:
  clang/include/clang/Basic/LangOptions.def
  clang/include/clang/Driver/CC1Options.td
  clang/lib/Frontend/CompilerInvocation.cpp
  clang/lib/Sema/Sema.cpp


Index: clang/lib/Sema/Sema.cpp
===================================================================
--- clang/lib/Sema/Sema.cpp
+++ clang/lib/Sema/Sema.cpp
@@ -981,6 +981,14 @@
                                  LateParsedInstantiations.begin(),
                                  LateParsedInstantiations.end());
     LateParsedInstantiations.clear();
+
+    // FIXME: Instantiating implicit templates already in the PCH breaks some
+    // OpenMP-specific code paths, see https://reviews.llvm.org/D69585 .
+    if(LangOpts.PCHInstantiateTemplates && !LangOpts.OpenMP) {
+      llvm::TimeTraceScope TimeScope("PerformPendingInstantiations",
+                                     StringRef(""));
+      PerformPendingInstantiations();
+    }
   }
 
   DiagnoseUnterminatedPragmaPack();
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -3223,6 +3223,7 @@
 
   Opts.CompleteMemberPointers = Args.hasArg(OPT_fcomplete_member_pointers);
   Opts.BuildingPCHWithObjectFile = Args.hasArg(OPT_building_pch_with_obj);
+  Opts.PCHInstantiateTemplates = Args.hasArg(OPT_pch_instantiate_templates);
 }
 
 static bool isStrictlyPreprocessorAction(frontend::ActionKind Action) {
Index: clang/include/clang/Driver/CC1Options.td
===================================================================
--- clang/include/clang/Driver/CC1Options.td
+++ clang/include/clang/Driver/CC1Options.td
@@ -672,6 +672,8 @@
   HelpText<"Disable inclusion of timestamp in precompiled headers">;
 def building_pch_with_obj : Flag<["-"], "building-pch-with-obj">,
   HelpText<"This compilation is part of building a PCH with corresponding object file.">;
+def pch_instantiate_templates : Flag<["-"], "pch-instantiate-templates">,
+  HelpText<"Perform pending template instantiations already while building the PCH.">;
 
 def aligned_alloc_unavailable : Flag<["-"], "faligned-alloc-unavailable">,
   HelpText<"Aligned allocation/deallocation functions are unavailable">;
Index: clang/include/clang/Basic/LangOptions.def
===================================================================
--- clang/include/clang/Basic/LangOptions.def
+++ clang/include/clang/Basic/LangOptions.def
@@ -160,6 +160,7 @@
 BENIGN_LANGOPT(CompilingPCH, 1, 0, "building a pch")
 BENIGN_LANGOPT(BuildingPCHWithObjectFile, 1, 0, "building a pch which has a corresponding object file")
 BENIGN_LANGOPT(CacheGeneratedPCH, 1, 0, "cache generated PCH files in memory")
+BENIGN_LANGOPT(PCHInstantiateTemplates, 1, 0, "performing pending template instantiations already while building a pch")
 COMPATIBLE_LANGOPT(ModulesDeclUse    , 1, 0, "require declaration of module uses")
 BENIGN_LANGOPT(ModulesSearchAll  , 1, 1, "searching even non-imported modules to find unresolved references")
 COMPATIBLE_LANGOPT(ModulesStrictDeclUse, 1, 0, "requiring declaration of module uses and all headers to be in modules")


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