Trigger SIL parsing from performSILGeneration

Rather than eagerly parsing an input .sil file
in `performSemaUpTo`, trigger it from
`performSILGeneration`. This will allow us to
remove the SILModule stored on the
CompilerInstance and will eventually allow the
various SIL tools to just call into
`performSILGeneration` without needing to call
`performSema`.

Author: hamishknight

lib/Frontend/Frontend.cpp

@@ -814,13 +814,6 @@ void CompilerInstance::performSemaUpTo(SourceFile::ASTStage_t LimitStage) {
 
   forEachFileToTypeCheck([&](SourceFile &SF) {
     performTypeChecking(SF);
-
-    // Parse the SIL decls if needed.
-    // TODO: Requestify SIL parsing.
-    if (TheSILModule) {
-      SILParserState SILContext(TheSILModule.get());
-      parseSourceFileSIL(SF, &SILContext);
-    }
   });
 
   finishTypeChecking();

lib/FrontendTool/FrontendTool.cpp

@@ -1066,17 +1066,11 @@ static bool performCompileStepsPostSILGen(CompilerInstance &Instance,
 static bool performCompileStepsPostSema(CompilerInstance &Instance,
                                         int &ReturnValue,
                                         FrontendObserver *observer) {
-  auto mod = Instance.getMainModule();
-  if (auto SM = Instance.takeSILModule()) {
-    const PrimarySpecificPaths PSPs =
-        Instance.getPrimarySpecificPathsForAtMostOnePrimary();
-    return performCompileStepsPostSILGen(Instance, std::move(SM), mod, PSPs,
-                                         ReturnValue, observer);
-  }
-
   const auto &Invocation = Instance.getInvocation();
   const SILOptions &SILOpts = Invocation.getSILOptions();
   const FrontendOptions &opts = Invocation.getFrontendOptions();
+
+  auto *mod = Instance.getMainModule();
   if (!opts.InputsAndOutputs.hasPrimaryInputs()) {
     // If there are no primary inputs the compiler is in WMO mode and builds one
     // SILModule for the entire module.

lib/SILGen/SILGen.cpp

@@ -1860,6 +1860,11 @@ class SILGenModuleRAII {
 std::unique_ptr<SILModule>
 SILGenSourceFileRequest::evaluate(Evaluator &evaluator,
                                   SILGenDescriptor desc) const {
+  // If we have a .sil file to parse, defer to the parsing request.
+  if (desc.getSourceFileToParse()) {
+    return llvm::cantFail(evaluator(ParseSILModuleRequest{desc}));
+  }
+
   auto *unit = desc.context.get<FileUnit *>();
   auto *mod = unit->getParentModule();
   auto M = std::unique_ptr<SILModule>(
@@ -1879,6 +1884,11 @@ SILGenSourceFileRequest::evaluate(Evaluator &evaluator,
 std::unique_ptr<SILModule>
 SILGenWholeModuleRequest::evaluate(Evaluator &evaluator,
                                    SILGenDescriptor desc) const {
+  // If we have a .sil file to parse, defer to the parsing request.
+  if (desc.getSourceFileToParse()) {
+    return llvm::cantFail(evaluator(ParseSILModuleRequest{desc}));
+  }
+
   auto *mod = desc.context.get<ModuleDecl *>();
   auto M = std::unique_ptr<SILModule>(
       new SILModule(mod, desc.conv, desc.opts, mod, /*wholeModule*/ true));