[LoopGuardWidening] Split out a loop pass version of GuardWidening

The idea is to have a pass which performs the same transformation as GuardWidening, but can be run within a loop pass manager without disrupting the pass manager structure.  As demonstrated by the test case, this doesn't quite get there because of issues with post dom, but it gives a good step in the right direction.  the motivation is purely to reduce compile time since we can now preserve locality during the loop walk.

This patch only includes a legacy pass.  A follow up will add a new style pass as well.

llvm-svn: 331060

llvm/include/llvm/InitializePasses.h

@@ -162,6 +162,7 @@ void initializeGlobalOptLegacyPassPass(PassRegistry&);
 void initializeGlobalSplitPass(PassRegistry&);
 void initializeGlobalsAAWrapperPassPass(PassRegistry&);
 void initializeGuardWideningLegacyPassPass(PassRegistry&);
+void initializeLoopGuardWideningLegacyPassPass(PassRegistry&);
 void initializeIPCPPass(PassRegistry&);
 void initializeIPSCCPLegacyPassPass(PassRegistry&);
 void initializeIRTranslatorPass(PassRegistry&);

llvm/include/llvm/LinkAllPasses.h

@@ -111,6 +111,7 @@ namespace {
       (void) llvm::createGlobalOptimizerPass();
       (void) llvm::createGlobalsAAWrapperPass();
       (void) llvm::createGuardWideningPass();
+      (void) llvm::createLoopGuardWideningPass();
       (void) llvm::createIPConstantPropagationPass();
       (void) llvm::createIPSCCPPass();
       (void) llvm::createInductiveRangeCheckEliminationPass();

llvm/include/llvm/Transforms/Scalar.h

@@ -97,6 +97,16 @@ FunctionPass *createAggressiveDCEPass();
 FunctionPass *createGuardWideningPass();
 
 
+//===----------------------------------------------------------------------===//
+//
+// LoopGuardWidening - Analogous to the GuardWidening pass, but restricted to a
+// single loop at a time for use within a LoopPassManager.  Desired effect is
+// to widen guards into preheader or a single guard within loop if that's not
+// possible.
+//
+Pass *createLoopGuardWideningPass();
+
+
 //===----------------------------------------------------------------------===//
 //
 // BitTrackingDCE - This pass uses a bit-tracking DCE algorithm in order to

llvm/lib/Transforms/Scalar/GuardWidening.cpp

@@ -40,9 +40,11 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Scalar/GuardWidening.h"
+#include <functional>
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/PostDominators.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/ConstantRange.h"
@@ -53,6 +55,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
 
 using namespace llvm;
 
@@ -65,6 +68,11 @@ class GuardWideningImpl {
   PostDominatorTree &PDT;
   LoopInfo &LI;
 
+  /// Together, these describe the region of interest.  This might be all of
+  /// the blocks within a function, or only a given loop's blocks and preheader.
+  DomTreeNode *Root;
+  std::function<bool(BasicBlock*)> BlockFilter;
+
   /// The set of guards whose conditions have been widened into dominating
   /// guards.
   SmallVector<IntrinsicInst *, 16> EliminatedGuards;
@@ -205,9 +213,11 @@ class GuardWideningImpl {
   }
 
 public:
+
   explicit GuardWideningImpl(DominatorTree &DT, PostDominatorTree &PDT,
-                             LoopInfo &LI)
-      : DT(DT), PDT(PDT), LI(LI) {}
+                             LoopInfo &LI, DomTreeNode *Root,
+                             std::function<bool(BasicBlock*)> BlockFilter)
+    : DT(DT), PDT(PDT), LI(LI), Root(Root), BlockFilter(BlockFilter) {}
 
   /// The entry point for this pass.
   bool run();
@@ -220,9 +230,12 @@ bool GuardWideningImpl::run() {
   DenseMap<BasicBlock *, SmallVector<IntrinsicInst *, 8>> GuardsInBlock;
   bool Changed = false;
 
-  for (auto DFI = df_begin(DT.getRootNode()), DFE = df_end(DT.getRootNode());
+  for (auto DFI = df_begin(Root), DFE = df_end(Root);
        DFI != DFE; ++DFI) {
     auto *BB = (*DFI)->getBlock();
+    if (!BlockFilter(BB))
+      continue;
+
     auto &CurrentList = GuardsInBlock[BB];
 
     for (auto &I : *BB)
@@ -233,6 +246,7 @@ bool GuardWideningImpl::run() {
       Changed |= eliminateGuardViaWidening(II, DFI, GuardsInBlock);
   }
 
+  assert(EliminatedGuards.empty() || Changed);
   for (auto *II : EliminatedGuards)
     if (!WidenedGuards.count(II))
       II->eraseFromParent();
@@ -252,6 +266,8 @@ bool GuardWideningImpl::eliminateGuardViaWidening(
   // for the most profit.
   for (unsigned i = 0, e = DFSI.getPathLength(); i != e; ++i) {
     auto *CurBB = DFSI.getPath(i)->getBlock();
+    if (!BlockFilter(CurBB))
+      break;
     auto *CurLoop = LI.getLoopFor(CurBB);
     assert(GuardsInBlock.count(CurBB) && "Must have been populated by now!");
     const auto &GuardsInCurBB = GuardsInBlock.find(CurBB)->second;
@@ -647,7 +663,8 @@ PreservedAnalyses GuardWideningPass::run(Function &F,
   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
   auto &LI = AM.getResult<LoopAnalysis>(F);
   auto &PDT = AM.getResult<PostDominatorTreeAnalysis>(F);
-  if (!GuardWideningImpl(DT, PDT, LI).run())
+  if (!GuardWideningImpl(DT, PDT, LI, DT.getRootNode(),
+                         [](BasicBlock*) { return true; } ).run())
     return PreservedAnalyses::all();
 
   PreservedAnalyses PA;
@@ -658,7 +675,6 @@ PreservedAnalyses GuardWideningPass::run(Function &F,
 namespace {
 struct GuardWideningLegacyPass : public FunctionPass {
   static char ID;
-  GuardWideningPass Impl;
 
   GuardWideningLegacyPass() : FunctionPass(ID) {
     initializeGuardWideningLegacyPassPass(*PassRegistry::getPassRegistry());
@@ -667,10 +683,11 @@ struct GuardWideningLegacyPass : public FunctionPass {
   bool runOnFunction(Function &F) override {
     if (skipFunction(F))
       return false;
-    return GuardWideningImpl(
-               getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
-               getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree(),
-               getAnalysis<LoopInfoWrapperPass>().getLoopInfo()).run();
+    auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+    auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+    auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
+    return GuardWideningImpl(DT, PDT, LI, DT.getRootNode(),
+                         [](BasicBlock*) { return true; } ).run();
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
@@ -680,9 +697,43 @@ struct GuardWideningLegacyPass : public FunctionPass {
     AU.addRequired<LoopInfoWrapperPass>();
   }
 };
+
+/// Same as above, but restricted to a single loop at a time.  Can be
+/// scheduled with other loop passes w/o breaking out of LPM
+struct LoopGuardWideningLegacyPass : public LoopPass {
+  static char ID;
+
+  LoopGuardWideningLegacyPass() : LoopPass(ID) {
+    initializeLoopGuardWideningLegacyPassPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnLoop(Loop *L, LPPassManager &LPM) override {
+    if (skipLoop(L))
+      return false;
+    auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+    auto &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+    auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
+    BasicBlock *RootBB = L->getLoopPredecessor();
+    if (!RootBB)
+      RootBB = L->getHeader();
+    auto BlockFilter = [&](BasicBlock *BB) {
+      return BB == RootBB || L->contains(BB);
+    };
+    return GuardWideningImpl(DT, PDT, LI,
+                             DT.getNode(RootBB), BlockFilter).run();
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    getLoopAnalysisUsage(AU);
+    AU.addRequired<PostDominatorTreeWrapperPass>();
+    AU.addPreserved<PostDominatorTreeWrapperPass>();
+  }
+};
 }
 
 char GuardWideningLegacyPass::ID = 0;
+char LoopGuardWideningLegacyPass::ID = 0;
 
 INITIALIZE_PASS_BEGIN(GuardWideningLegacyPass, "guard-widening", "Widen guards",
                       false, false)
@@ -692,6 +743,20 @@ INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
 INITIALIZE_PASS_END(GuardWideningLegacyPass, "guard-widening", "Widen guards",
                     false, false)
 
+INITIALIZE_PASS_BEGIN(LoopGuardWideningLegacyPass, "loop-guard-widening",
+                      "Widen guards (within a single loop, as a loop pass)",
+                      false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(PostDominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_END(LoopGuardWideningLegacyPass, "loop-guard-widening",
+                    "Widen guards (within a single loop, as a loop pass)",
+                    false, false)
+
 FunctionPass *llvm::createGuardWideningPass() {
   return new GuardWideningLegacyPass();
 }
+
+Pass *llvm::createLoopGuardWideningPass() {
+  return new LoopGuardWideningLegacyPass();
+}

llvm/lib/Transforms/Scalar/Scalar.cpp

@@ -45,6 +45,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializeScalarizerPass(Registry);
   initializeDSELegacyPassPass(Registry);
   initializeGuardWideningLegacyPassPass(Registry);
+  initializeLoopGuardWideningLegacyPassPass(Registry);
   initializeGVNLegacyPassPass(Registry);
   initializeNewGVNLegacyPassPass(Registry);
   initializeEarlyCSELegacyPassPass(Registry);

llvm/test/Transforms/GuardWidening/loop-schedule.ll

@@ -0,0 +1,41 @@
+; RUN: opt -S -licm -loop-guard-widening -licm -debug-pass=Structure < %s 2>&1   | FileCheck %s
+
+; Main point of this test is to check the scheduling -- there should be
+; no analysis passes needed between LICM and LoopGuardWidening
+
+; TODO: Because guard widdening currently requires post-dom, we end up
+; breaking the loop pass manager to compute it.  Need to either make all
+; loop passes preserve postdom (hard) or make it optional in guard widdening
+; CHECK: Loop Pass Manager
+; CHECK:   Loop Invariant Code Motion
+; CHECK: Post-Dominator Tree Construction
+; CHECK: Loop Pass Manager
+; CHECK:   Widen guards (within a single loop, as a loop pass)
+; CHECK:   Loop Invariant Code Motion
+
+declare void @llvm.experimental.guard(i1,...)
+
+define void @iter(i32 %a, i32 %b, i1* %c_p) {
+; CHECK-LABEL @iter
+; CHECK:  %cond_0 = icmp ult i32 %a, 10
+; CHECK:  %cond_1 = icmp ult i32 %b, 10
+; CHECK:  %wide.chk = and i1 %cond_0, %cond_1
+; CHECK:  call void (i1, ...) @llvm.experimental.guard(i1 %wide.chk) [ "deopt"() ]
+
+entry:
+  %cond_0 = icmp ult i32 %a, 10
+  call void (i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ]
+  br label %loop
+
+loop:                                             ; preds = %loop.preheader, %loop
+  %cond_1 = icmp ult i32 %b, 10
+  call void (i1, ...) @llvm.experimental.guard(i1 %cond_1) [ "deopt"() ]
+  %cnd = load i1, i1* %c_p
+  br i1 %cnd, label %loop, label %leave.loopexit
+
+leave.loopexit:                                   ; preds = %loop
+  br label %leave
+
+leave:                                            ; preds = %leave.loopexit, %entry
+  ret void
+}