[LDist] Match behavior between invoking via optimization pipeline or opt -loop-distribute

In r267672, where the loop distribution pragma was introduced, I tried
it hard to keep the old behavior for opt: when opt is invoked
with -loop-distribute, it should distribute the loop (it's off by
default when ran via the optimization pipeline).

As MichaelZ has discovered this has the unintended consequence of
breaking a very common developer work-flow to reproduce compilations
using opt: First you print the pass pipeline of clang
with -debug-pass=Arguments and then invoking opt with the returned
arguments.

clang -debug-pass will include -loop-distribute but the pass is invoked
with default=off so nothing happens unless the loop carries the pragma.
While through opt (default=on) we will try to distribute all loops.

This changes opt's default to off as well to match clang.  The tests are
modified to explicitly enable the transformation.

llvm-svn: 290235

2 files changed, 9 insertions, 32 deletions

diff --git a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
index 264bc3260b8..724965e27ff 100644
--- a/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
+++ b/llvm/lib/Transforms/IPO/PassManagerBuilder.cpp
@@ -561,7 +561,7 @@ void PassManagerBuilder::populateModulePassManager(
   // into separate loop that would otherwise inhibit vectorization.  This is
   // currently only performed for loops marked with the metadata
   // llvm.loop.distribute=true or when -enable-loop-distribute is specified.
-  MPM.add(createLoopDistributePass(/*ProcessAllLoopsByDefault=*/false));
+  MPM.add(createLoopDistributePass());
 
   MPM.add(createLoopVectorizePass(DisableUnrollLoops, LoopVectorize));
 
diff --git a/llvm/lib/Transforms/Scalar/LoopDistribute.cpp b/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
index 1da0fd8d2a8..b2b2f72aa83 100644
--- a/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDistribute.cpp
@@ -73,11 +73,10 @@ static cl::opt<unsigned> PragmaDistributeSCEVCheckThreshold(
         "The maximum number of SCEV checks allowed for Loop "
         "Distribution for loop marked with #pragma loop distribute(enable)"));
 
-// Note that the initial value for this depends on whether the pass is invoked
-// directly or from the optimization pipeline.
 static cl::opt<bool> EnableLoopDistribute(
     "enable-loop-distribute", cl::Hidden,
-    cl::desc("Enable the new, experimental LoopDistribution Pass"));
+    cl::desc("Enable the new, experimental LoopDistribution Pass"),
+    cl::init(false));
 
 STATISTIC(NumLoopsDistributed, "Number of loops distributed");
 
@@ -875,8 +874,7 @@ private:
 /// Shared implementation between new and old PMs.
 static bool runImpl(Function &F, LoopInfo *LI, DominatorTree *DT,
                     ScalarEvolution *SE, OptimizationRemarkEmitter *ORE,
-                    std::function<const LoopAccessInfo &(Loop &)> &GetLAA,
-                    bool ProcessAllLoops) {
+                    std::function<const LoopAccessInfo &(Loop &)> &GetLAA) {
   // Build up a worklist of inner-loops to vectorize. This is necessary as the
   // act of distributing a loop creates new loops and can invalidate iterators
   // across the loops.
@@ -895,7 +893,7 @@ static bool runImpl(Function &F, LoopInfo *LI, DominatorTree *DT,
 
     // If distribution was forced for the specific loop to be
     // enabled/disabled, follow that.  Otherwise use the global flag.
-    if (LDL.isForced().getValueOr(ProcessAllLoops))
+    if (LDL.isForced().getValueOr(EnableLoopDistribute))
       Changed |= LDL.processLoop(GetLAA);
   }
 
@@ -906,15 +904,8 @@ static bool runImpl(Function &F, LoopInfo *LI, DominatorTree *DT,
 /// \brief The pass class.
 class LoopDistributeLegacy : public FunctionPass {
 public:
-  /// \p ProcessAllLoopsByDefault specifies whether loop distribution should be
-  /// performed by default.  Pass -enable-loop-distribute={0,1} overrides this
-  /// default.  We use this to keep LoopDistribution off by default when invoked
-  /// from the optimization pipeline but on when invoked explicitly from opt.
-  LoopDistributeLegacy(bool ProcessAllLoopsByDefault = true)
-      : FunctionPass(ID), ProcessAllLoops(ProcessAllLoopsByDefault) {
+  LoopDistributeLegacy() : FunctionPass(ID) {
     // The default is set by the caller.
-    if (EnableLoopDistribute.getNumOccurrences() > 0)
-      ProcessAllLoops = EnableLoopDistribute;
     initializeLoopDistributeLegacyPass(*PassRegistry::getPassRegistry());
   }
 
@@ -930,7 +921,7 @@ public:
     std::function<const LoopAccessInfo &(Loop &)> GetLAA =
         [&](Loop &L) -> const LoopAccessInfo & { return LAA->getInfo(&L); };
 
-    return runImpl(F, LI, DT, SE, ORE, GetLAA, ProcessAllLoops);
+    return runImpl(F, LI, DT, SE, ORE, GetLAA);
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
@@ -945,23 +936,11 @@ public:
   }
 
   static char ID;
-
-private:
-  /// \brief Whether distribution should be on in this function.  The per-loop
-  /// pragma can override this.
-  bool ProcessAllLoops;
 };
 } // anonymous namespace
 
 PreservedAnalyses LoopDistributePass::run(Function &F,
                                           FunctionAnalysisManager &AM) {
-  // FIXME: This does not currently match the behavior from the old PM.
-  // ProcessAllLoops with the old PM defaults to true when invoked from opt and
-  // false when invoked from the optimization pipeline.
-  bool ProcessAllLoops = false;
-  if (EnableLoopDistribute.getNumOccurrences() > 0)
-    ProcessAllLoops = EnableLoopDistribute;
-
   auto &LI = AM.getResult<LoopAnalysis>(F);
   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
   auto &SE = AM.getResult<ScalarEvolutionAnalysis>(F);
@@ -973,7 +952,7 @@ PreservedAnalyses LoopDistributePass::run(Function &F,
     return LAM.getResult<LoopAccessAnalysis>(L);
   };
 
-  bool Changed = runImpl(F, &LI, &DT, &SE, &ORE, GetLAA, ProcessAllLoops);
+  bool Changed = runImpl(F, &LI, &DT, &SE, &ORE, GetLAA);
   if (!Changed)
     return PreservedAnalyses::all();
   PreservedAnalyses PA;
@@ -996,7 +975,5 @@ INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
 INITIALIZE_PASS_END(LoopDistributeLegacy, LDIST_NAME, ldist_name, false, false)
 
 namespace llvm {
-FunctionPass *createLoopDistributePass(bool ProcessAllLoopsByDefault) {
-  return new LoopDistributeLegacy(ProcessAllLoopsByDefault);
-}
+FunctionPass *createLoopDistributePass() { return new LoopDistributeLegacy(); }
 }