[llvm] r335317 - [LegacyPM] Fix PR37888 by teaching the legacy loop pass manager how to

[Chandler Carruth via llvm-commits]

Author: chandlerc
Date: Thu Jun 21 19:43:41 2018
New Revision: 335317

URL: http://llvm.org/viewvc/llvm-project?rev=335317&view=rev
Log:
[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

Added:
    llvm/trunk/test/Transforms/SimpleLoopUnswitch/pr37888.ll
Modified:
    llvm/trunk/lib/Analysis/LoopPass.cpp

Modified: llvm/trunk/lib/Analysis/LoopPass.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/LoopPass.cpp?rev=335317&r1=335316&r2=335317&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/LoopPass.cpp (original)
+++ llvm/trunk/lib/Analysis/LoopPass.cpp Thu Jun 21 19:43:41 2018
@@ -142,8 +142,17 @@ void LPPassManager::getAnalysisUsage(Ana
 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

Added: llvm/trunk/test/Transforms/SimpleLoopUnswitch/pr37888.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimpleLoopUnswitch/pr37888.ll?rev=335317&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SimpleLoopUnswitch/pr37888.ll (added)
+++ llvm/trunk/test/Transforms/SimpleLoopUnswitch/pr37888.ll Thu Jun 21 19:43:41 2018
@@ -0,0 +1,38 @@
+; RUN: opt -simple-loop-unswitch -loop-deletion -S < %s | FileCheck %s
+;
+; Check that when we do unswitching where we re-enqueue the loop to be processed
+; again, but manage to delete the loop before ever getting to iterate on it, it
+; doesn't crash the legacy pass manager.
+
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @pr37888() {
+; CHECK-LABEL: define void @pr37888()
+entry:
+  %tobool = icmp ne i16 undef, 0
+  br label %for.body
+; CHECK:         %[[TOBOOL:.*]] = icmp ne
+; CHECK-NEXT:    br i1 %[[TOBOOL]], label %if.then, label %[[ENTRY_SPLIT:.*]]
+;
+; CHECK:       [[ENTRY_SPLIT]]:
+; CHECK-NEXT:    br label %for.end
+
+for.body:
+  br i1 %tobool, label %if.then, label %if.end
+
+if.then:
+  unreachable
+; CHECK:       if.then:
+; CHECK-NEXT:    unreachable
+
+if.end:
+  br label %for.inc
+
+for.inc:
+  br i1 undef, label %for.body, label %for.end
+
+for.end:
+  ret void
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+}