[NFC] Remove FIXMEs about calling LLVMContext::yield()

[aeubanks]

Summary

Nobody has complained about this, and the documentation for
LLVMContext::yield() states that LLVM is allowed to never call it.

llvm/include/llvm/IR/PassManager.h

for (unsigned Idx = 0, Size = Passes.size(); Idx != Size; ++Idx) {
 
       // Update the analysis manager as each pass runs and potentially
       // invalidates analyses.
       AM.invalidate(IR, PassPA);
 
       // Finally, intersect the preserved analyses to compute the aggregate
       // preserved set for this pass manager.
       PA.intersect(std::move(PassPA));
-
-      // FIXME: Historically, the pass managers all called the LLVM context's
-      // yield function here. We don't have a generic way to acquire the
-      // context and it isn't yet clear what the right pattern is for yielding
-      // in the new pass manager so it is currently omitted.
-      //IR.getContext().yield();
     }
 
     // Invalidation was handled after each pass in the above loop for the
     // current unit of IR. Therefore, the remaining analysis results in the
     // AnalysisManager are preserved. We mark this with a set so that we don't
     // need to inspect each one individually.
     PA.preserveSet<AllAnalysesOn<IRUnitT>>();
 

llvm/lib/Analysis/CGSCCPassManager.cpp

for (auto &Pass : Passes) {
 
     // Update the analysis manager as each pass runs and potentially
     // invalidates analyses.
     AM.invalidate(*C, PassPA);
 
     // Finally, we intersect the final preserved analyses to compute the
     // aggregate preserved set for this pass manager.
     PA.intersect(std::move(PassPA));
-
-    // FIXME: Historically, the pass managers all called the LLVM context's
-    // yield function here. We don't have a generic way to acquire the
-    // context and it isn't yet clear what the right pattern is for yielding
-    // in the new pass manager so it is currently omitted.
-    // ...getContext().yield();
   }
 
   // Before we mark all of *this* SCC's analyses as preserved below, intersect
   // this with the cross-SCC preserved analysis set. This is used to allow
   // CGSCC passes to mutate ancestor SCCs and still trigger proper invalidation
   // for them.
   UR.CrossSCCPA.intersect(PA);
 

llvm/lib/Transforms/Scalar/LoopPassManager.cpp

for (size_t I = 0, E = IsLoopNestPass.size(); I != E; ++I) {
 
     // Check if the current pass preserved the loop-nest object or not.
     IsLoopNestPtrValid &= PassPA->getChecker<LoopNestAnalysis>().preserved();
 
     // After running the loop pass, the parent loop might change and we need to
     // notify the updater, otherwise U.ParentL might gets outdated and triggers
     // assertion failures in addSiblingLoops and addChildLoops.
     U.setParentLoop(L.getParentLoop());
-
-    // FIXME: Historically, the pass managers all called the LLVM context's
-    // yield function here. We don't have a generic way to acquire the
-    // context and it isn't yet clear what the right pattern is for yielding
-    // in the new pass manager so it is currently omitted.
-    // ...getContext().yield();
   }
   return PA;
 }
 
 // Run all loop passes on loop \p L. Loop-nest passes don't run either because
 // \p L is not a top-level one or simply because there are no loop-nest passes
 // in the pass manager at all.
 PreservedAnalyses
for (auto &Pass : LoopPasses) {
     // Finally, we intersect the final preserved analyses to compute the
     // aggregate preserved set for this pass manager.
     PA.intersect(std::move(*PassPA));
 
     // After running the loop pass, the parent loop might change and we need to
     // notify the updater, otherwise U.ParentL might gets outdated and triggers
     // assertion failures in addSiblingLoops and addChildLoops.
     U.setParentLoop(L.getParentLoop());
-
-    // FIXME: Historically, the pass managers all called the LLVM context's
-    // yield function here. We don't have a generic way to acquire the
-    // context and it isn't yet clear what the right pattern is for yielding
-    // in the new pass manager so it is currently omitted.
-    // ...getContext().yield();
   }
   return PA;
 }
 } // namespace llvm
 
 void FunctionToLoopPassAdaptor::printPipeline(
     raw_ostream &OS, function_ref<StringRef(StringRef)> MapClassName2PassName) {
   OS << (UseMemorySSA ? "loop-mssa(" : "loop(");