[LegacyPM] Fix PR37888 by teaching the legacy loop pass manager how to

clear out deleted loops from the current queue beyond just the current
loop.

This is important because SimpleLoopUnswitch will now enqueue the same
loop to be re-processed. When it does this with the legacy PM, we don't
have a way of canceling the rest of the pipeline and so we can end up
deleting the loop before we reprocess it. =/

This change also makes it easy to support deleting other loops in the
queue to process, although I don't have any use cases for that.

Differential Revision: https://reviews.llvm.org/D48470

llvm-svn: 335317

1 files changed, 10 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/LoopPass.cpp b/llvm/lib/Analysis/LoopPass.cpp
index 00d88e8189e..c5ced03cfa8 100644
--- a/llvm/lib/Analysis/LoopPass.cpp
+++ b/llvm/lib/Analysis/LoopPass.cpp
@@ -142,8 +142,17 @@ void LPPassManager::getAnalysisUsage(AnalysisUsage &Info) const {
 void LPPassManager::markLoopAsDeleted(Loop &L) {
   assert((&L == CurrentLoop || CurrentLoop->contains(&L)) &&
          "Must not delete loop outside the current loop tree!");
-  if (&L == CurrentLoop)
+  // If this loop appears elsewhere within the queue, we also need to remove it
+  // there. However, we have to be careful to not remove the back of the queue
+  // as that is assumed to match the current loop.
+  assert(LQ.back() == CurrentLoop && "Loop queue back isn't the current loop!");
+  LQ.erase(std::remove(LQ.begin(), LQ.end(), &L), LQ.end());
+
+  if (&L == CurrentLoop) {
     CurrentLoopDeleted = true;
+    // Add this loop back onto the back of the queue to preserve our invariants.
+    LQ.push_back(&L);
+  }
 }
 
 /// run - Execute all of the passes scheduled for execution.  Keep track of