Add/fix comments as a follow-up to the string constants optimization changes.

Author: eeckstein

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -384,6 +384,7 @@ static void addClosureSpecializePassPipeline(SILPassPipelinePlan &P) {
   P.addDeadObjectElimination();
 
   // These few passes are needed to cleanup between loop unrolling and GlobalOpt.
+  // This is needed to fully optimize static small String constants.
   P.addSimplifyCFG();
   P.addSILCombine();
   P.addPerformanceConstantPropagation();

lib/SILOptimizer/SILCombiner/SILCombinerMiscVisitors.cpp

@@ -473,7 +473,7 @@ static SILValue isConstIndexAddr(SILValue val, unsigned &index) {
   auto *Index = dyn_cast<IntegerLiteralInst>(IA->getIndex());
 
   // Limiting to 32 bits is more than enough. The reason why not limiting to 64
-  // bits is to let room for overflow when we add two indices.
+  // bits is to leave room for overflow when we add two indices.
   if (!Index || Index->getValue().getActiveBits() > 32)
     return nullptr;