Add preparePassManager() hook. This allows each pass to check whether

current active pass manager is appropriate or not.

A loop pass may consider current LPPassManager in appropraite if loop
pass is not preserving analysis information that is used by other
passes managed by current LPPassManager. In such situation, loop pass
can pop current LPPassManager from the PMStack using this  hook
and use new LPPassManager for itself.

llvm-svn: 34941

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/lib/VMCore/PassManager.cpp b/llvm/lib/VMCore/PassManager.cpp
index 23a26130fc3..25353082433 100644
--- a/llvm/lib/VMCore/PassManager.cpp
+++ b/llvm/lib/VMCore/PassManager.cpp
@@ -385,6 +385,9 @@ void PMTopLevelManager::schedulePass(Pass *P) {
   if (findAnalysisPass(P->getPassInfo()))
       return;
 
+  // Give pass a chance to prepare the stage.
+  P->preparePassManager(activeStack);
+
   AnalysisUsage AnUsage;
   P->getAnalysisUsage(AnUsage);
   const std::vector<AnalysisID> &RequiredSet = AnUsage.getRequiredSet();