[OpenMP] Fix the OpenMPOpt pass incorrectly optimizing if definition was missing

Summary:
This code is intended to block transformations if the call isn't
present, however the way it's coded it silently lets it pass if the
definition doesn't exist at all. This previously was always valid since
we included the runtime as one giant blob so everything was always
there, but now that we want to move towards separate ones, it's not
quite correct.

Author: jhuber6

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -969,7 +969,7 @@ PassBuilder::buildInlinerPipeline(OptimizationLevel Level,
   // Try to perform OpenMP specific optimizations. This is a (quick!) no-op if
   // there are no OpenMP runtime calls present in the module.
   if (Level == OptimizationLevel::O2 || Level == OptimizationLevel::O3)
-    MainCGPipeline.addPass(OpenMPOptCGSCCPass());
+    MainCGPipeline.addPass(OpenMPOptCGSCCPass(Phase));
 
   invokeCGSCCOptimizerLateEPCallbacks(MainCGPipeline, Level);
 
@@ -1137,7 +1137,7 @@ PassBuilder::buildModuleSimplificationPipeline(OptimizationLevel Level,
 
   // Try to perform OpenMP specific optimizations on the module. This is a
   // (quick!) no-op if there are no OpenMP runtime calls present in the module.
-  MPM.addPass(OpenMPOptPass());
+  MPM.addPass(OpenMPOptPass(Phase));
 
   if (AttributorRun & AttributorRunOption::MODULE)
     MPM.addPass(AttributorPass());

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

@@ -569,7 +569,7 @@ struct OMPInformationCache : public InformationCache {
     for (RuntimeFunction Fn : Fns) {
       RuntimeFunctionInfo &RFI = RFIs[Fn];
 
-      if (RFI.Declaration && RFI.Declaration->isDeclaration())
+      if (!RFI.Declaration || RFI.Declaration->isDeclaration())
         return false;
     }
     return true;
@@ -5792,6 +5792,7 @@ PreservedAnalyses OpenMPOptPass::run(Module &M, ModuleAnalysisManager &AM) {
   CallGraphUpdater CGUpdater;
 
   bool PostLink = LTOPhase == ThinOrFullLTOPhase::FullLTOPostLink ||
+                  LTOPhase == ThinOrFullLTOPhase::ThinLTOPostLink ||
                   LTOPhase == ThinOrFullLTOPhase::ThinLTOPreLink;
   OMPInformationCache InfoCache(M, AG, Allocator, /*CGSCC*/ nullptr, PostLink);
 
@@ -5871,6 +5872,7 @@ PreservedAnalyses OpenMPOptCGSCCPass::run(LazyCallGraph::SCC &C,
   CGUpdater.initialize(CG, C, AM, UR);
 
   bool PostLink = LTOPhase == ThinOrFullLTOPhase::FullLTOPostLink ||
+                  LTOPhase == ThinOrFullLTOPhase::ThinLTOPostLink ||
                   LTOPhase == ThinOrFullLTOPhase::ThinLTOPreLink;
   SetVector<Function *> Functions(SCC.begin(), SCC.end());
   OMPInformationCache InfoCache(*(Functions.back()->getParent()), AG, Allocator,