Add TODOs and update comments

Author: hassnaaHamdi

clang/docs/UsersManual.rst

@@ -2368,7 +2368,7 @@ are listed below.
    when there's a single implementation of the virtual function in the module.
    There could be a single implementation of the virtual function
    either because the function is not overridden in any derived class,
-   or because there is a single instantiated object that is using the function.
+   or because all objects are instances of the same class/type.
 
    Ex of IR before the optimization:
   .. code-block:: llvm

clang/lib/CodeGen/CGClass.cpp

@@ -2830,6 +2830,9 @@ void CodeGenFunction::EmitTypeMetadataCodeForVCall(const CXXRecordDecl *RD,
   // Emit the intrinsics of (type_test and assume) for the features of WPD and
   // speculative devirtualization. For WPD, emit the intrinsics only for the
   // case of non_public LTO visibility.
+  // TODO: refactor this condition and similar ones into a function (e.g.,
+  // ShouldEmitDevirtualizationMD) to encapsulate the details of the different
+  // types of devirtualization.
   else if ((CGM.getCodeGenOpts().WholeProgramVTables &&
             !CGM.AlwaysHasLTOVisibilityPublic(RD)) ||
            CGM.getCodeGenOpts().DevirtualizeSpeculatively) {

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -1666,6 +1666,8 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
   // Add devirtualization pass only when LTO is not enabled, as otherwise
   // the pass is already enabled in the LTO pipeline.
   if (PTO.DevirtualizeSpeculatively && LTOPhase == ThinOrFullLTOPhase::None) {
+    // TODO: explore a better pipeline configuration that can improve
+    // compilation time overhead.
     MPM.addPass(WholeProgramDevirtPass(
         /*ExportSummary*/ nullptr,
         /*ImportSummary*/ nullptr,