1 files changed, 19 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index 997ae616114..a2559bc70b1 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -138,10 +138,10 @@ static cl::opt<bool>
                               cl::Hidden,
                               cl::desc("Disable shrink-wrap library calls"));
 
-static cl::opt<bool>
-    EnableSimpleLoopUnswitch("enable-simple-loop-unswitch", cl::init(false),
-                             cl::Hidden,
-                             cl::desc("Enable the simple loop unswitch pass."));
+static cl::opt<bool> EnableSimpleLoopUnswitch(
+    "enable-simple-loop-unswitch", cl::init(false), cl::Hidden,
+    cl::desc("Enable the simple loop unswitch pass. Also enables independent "
+             "cleanup passes integrated into the loop pass manager pipeline."));
 
 static cl::opt<bool> EnableGVNSink(
     "enable-gvn-sink", cl::init(false), cl::Hidden,
@@ -335,6 +335,15 @@ void PassManagerBuilder::addFunctionSimplificationPasses(
   MPM.add(createTailCallEliminationPass()); // Eliminate tail calls
   MPM.add(createCFGSimplificationPass());     // Merge & remove BBs
   MPM.add(createReassociatePass());           // Reassociate expressions
+
+  // Begin the loop pass pipeline.
+  if (EnableSimpleLoopUnswitch) {
+    // The simple loop unswitch pass relies on separate cleanup passes. Schedule
+    // them first so when we re-process a loop they run before other loop
+    // passes.
+    MPM.add(createLoopInstSimplifyPass());
+    MPM.add(createLoopSimplifyCFGPass());
+  }
   // Rotate Loop - disable header duplication at -Oz
   MPM.add(createLoopRotatePass(SizeLevel == 2 ? 0 : -1));
   MPM.add(createLICMPass());                  // Hoist loop invariants
@@ -342,20 +351,26 @@ void PassManagerBuilder::addFunctionSimplificationPasses(
     MPM.add(createSimpleLoopUnswitchLegacyPass());
   else
     MPM.add(createLoopUnswitchPass(SizeLevel || OptLevel < 3, DivergentTarget));
+  // FIXME: We break the loop pass pipeline here in order to do full
+  // simplify-cfg. Eventually loop-simplifycfg should be enhanced to replace the
+  // need for this.
   MPM.add(createCFGSimplificationPass());
   addInstructionCombiningPass(MPM);
+  // We resume loop passes creating a second loop pipeline here.
   MPM.add(createIndVarSimplifyPass());        // Canonicalize indvars
   MPM.add(createLoopIdiomPass());             // Recognize idioms like memset.
   addExtensionsToPM(EP_LateLoopOptimizations, MPM);
   MPM.add(createLoopDeletionPass());          // Delete dead loops
 
   if (EnableLoopInterchange) {
+    // FIXME: These are function passes and break the loop pass pipeline.
     MPM.add(createLoopInterchangePass()); // Interchange loops
     MPM.add(createCFGSimplificationPass());
   }
   if (!DisableUnrollLoops)
     MPM.add(createSimpleLoopUnrollPass(OptLevel));    // Unroll small loops
   addExtensionsToPM(EP_LoopOptimizerEnd, MPM);
+  // This ends the loop pass pipelines.
 
   if (OptLevel > 1) {
     MPM.add(createMergedLoadStoreMotionPass()); // Merge ld/st in diamonds