[PM] Port SpeculativeExecution to new PM

[mkuper]

Summary

I'm a bit annoyed at having to keep a OnlyIfDivergentTarget variable in the legacy pass only because it changes the name of the class, but the other option is to query Impl for that - and I prefer a hack in the legacy version to a hack in the new version.

[davide]

I also prefer an hack in the old version. When I stumbled upon BasicBlock passes I first changed them to be function passes in the old PM and then did the transition. I guess in this case it's not really needed, and probably overkill. LGTM.

llvm/trunk/include/llvm/InitializePasses.h

 void initializeSeparateConstOffsetFromGEPPass(PassRegistry &);
 void initializeShadowStackGCLoweringPass(PassRegistry&);
 void initializeShrinkWrapPass(PassRegistry &);
 void initializeSimpleInlinerPass(PassRegistry&);
 void initializeSingleLoopExtractorPass(PassRegistry&);
 void initializeSinkingLegacyPassPass(PassRegistry&);
 void initializeSjLjEHPreparePass(PassRegistry&);
 void initializeSlotIndexesPass(PassRegistry&);
-void initializeSpeculativeExecutionPass(PassRegistry&);
+void initializeSpeculativeExecutionLegacyPassPass(PassRegistry&);
 void initializeSpillPlacementPass(PassRegistry&);
 void initializeStackColoringPass(PassRegistry&);
 void initializeStackMapLivenessPass(PassRegistry&);
 void initializeStackProtectorPass(PassRegistry&);
 void initializeStackSlotColoringPass(PassRegistry&);
 void initializeStraightLineStrengthReducePass(PassRegistry &);
 void initializeStripDeadDebugInfoPass(PassRegistry&);
 void initializeStripDeadPrototypesLegacyPassPass(PassRegistry&);

llvm/trunk/include/llvm/Transforms/Scalar/SpeculativeExecution.h

+//===- SpeculativeExecution.h -----------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass hoists instructions to enable speculative execution on
+// targets where branches are expensive. This is aimed at GPUs. It
+// currently works on simple if-then and if-then-else
+// patterns.
+//
+// Removing branches is not the only motivation for this
+// pass. E.g. consider this code and assume that there is no
+// addressing mode for multiplying by sizeof(*a):
+//
+//   if (b > 0)
+//     c = a[i + 1]
+//   if (d > 0)
+//     e = a[i + 2]
+//
+// turns into
+//
+//   p = &a[i + 1];
+//   if (b > 0)
+//     c = *p;
+//   q = &a[i + 2];
+//   if (d > 0)
+//     e = *q;
+//
+// which could later be optimized to
+//
+//   r = &a[i];
+//   if (b > 0)
+//     c = r[1];
+//   if (d > 0)
+//     e = r[2];
+//
+// Later passes sink back much of the speculated code that did not enable
+// further optimization.
+//
+// This pass is more aggressive than the function SpeculativeyExecuteBB in
+// SimplifyCFG. SimplifyCFG will not speculate if no selects are introduced and
+// it will speculate at most one instruction. It also will not speculate if
+// there is a value defined in the if-block that is only used in the then-block.
+// These restrictions make sense since the speculation in SimplifyCFG seems
+// aimed at introducing cheap selects, while this pass is intended to do more
+// aggressive speculation while counting on later passes to either capitalize on
+// that or clean it up.
+//
+// If the pass was created by calling
+// createSpeculativeExecutionIfHasBranchDivergencePass or the
+// -spec-exec-only-if-divergent-target option is present, this pass only has an
+// effect on targets where TargetTransformInfo::hasBranchDivergence() is true;
+// on other targets, it is a nop.
+//
+// This lets you include this pass unconditionally in the IR pass pipeline, but
+// only enable it for relevant targets.
+//
+//===----------------------------------------------------------------------===//
+#ifndef LLVM_TRANSFORMS_SCALAR_SPECULATIVEEXECUTION_H
+#define LLVM_TRANSFORMS_SCALAR_SPECULATIVEEXECUTION_H
+
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/IR/PassManager.h"
+
+namespace llvm {
+class SpeculativeExecutionPass
+    : public PassInfoMixin<SpeculativeExecutionPass> {
+public:
+  SpeculativeExecutionPass(bool OnlyIfDivergentTarget = false);
+
+  PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
+
+  // Glue for old PM
+  bool runImpl(Function &F, TargetTransformInfo *TTI);
+
+private:
+  bool runOnBasicBlock(BasicBlock &B);
+  bool considerHoistingFromTo(BasicBlock &FromBlock, BasicBlock &ToBlock);
+
+  // If true, this pass is a nop unless the target architecture has branch
+  // divergence.  
+  const bool OnlyIfDivergentTarget = false;
+
+  TargetTransformInfo *TTI = nullptr;
+};
+}
+
+#endif //LLVM_TRANSFORMS_SCALAR_SPECULATIVEEXECUTION_H

llvm/trunk/lib/Passes/PassBuilder.cpp

 #include "llvm/Transforms/Scalar/MergedLoadStoreMotion.h"
 #include "llvm/Transforms/Scalar/NaryReassociate.h"
 #include "llvm/Transforms/Scalar/PartiallyInlineLibCalls.h"
 #include "llvm/Transforms/Scalar/Reassociate.h"
 #include "llvm/Transforms/Scalar/SCCP.h"
 #include "llvm/Transforms/Scalar/SROA.h"
 #include "llvm/Transforms/Scalar/SimplifyCFG.h"
 #include "llvm/Transforms/Scalar/Sink.h"
+#include "llvm/Transforms/Scalar/SpeculativeExecution.h"
 #include "llvm/Transforms/Scalar/TailRecursionElimination.h"
 #include "llvm/Transforms/Utils/AddDiscriminators.h"
 #include "llvm/Transforms/Utils/BreakCriticalEdges.h"
 #include "llvm/Transforms/Utils/LCSSA.h"
 #include "llvm/Transforms/Utils/LoopSimplify.h"
 #include "llvm/Transforms/Utils/Mem2Reg.h"
 #include "llvm/Transforms/Utils/MemorySSA.h"
 #include "llvm/Transforms/Utils/SimplifyInstructions.h"

llvm/trunk/lib/Passes/PassRegistry.def

 FUNCTION_PASS("print<memoryssa>", MemorySSAPrinterPass(dbgs()))
 FUNCTION_PASS("print<regions>", RegionInfoPrinterPass(dbgs()))
 FUNCTION_PASS("print<scalar-evolution>", ScalarEvolutionPrinterPass(dbgs()))
 FUNCTION_PASS("reassociate", ReassociatePass())
 FUNCTION_PASS("sccp", SCCPPass())
 FUNCTION_PASS("simplify-cfg", SimplifyCFGPass())
 FUNCTION_PASS("sink", SinkingPass())
 FUNCTION_PASS("slp-vectorizer", SLPVectorizerPass())
+FUNCTION_PASS("speculative-execution", SpeculativeExecutionPass())
 FUNCTION_PASS("sroa", SROA())
 FUNCTION_PASS("tailcallelim", TailCallElimPass())
 FUNCTION_PASS("unreachableblockelim", UnreachableBlockElimPass())
 FUNCTION_PASS("verify", VerifierPass())
 FUNCTION_PASS("verify<domtree>", DominatorTreeVerifierPass())
 FUNCTION_PASS("verify<loops>", LoopVerifierPass())
 FUNCTION_PASS("verify<memoryssa>", MemorySSAVerifierPass())
 FUNCTION_PASS("verify<regions>", RegionInfoVerifierPass())

llvm/trunk/lib/Transforms/Scalar/Scalar.cpp

void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializeSCCPLegacyPassPass(Registry);
   initializeIPSCCPLegacyPassPass(Registry);
   initializeSROALegacyPassPass(Registry);
   initializeCFGSimplifyPassPass(Registry);
   initializeStructurizeCFGPass(Registry);
   initializeSinkingLegacyPassPass(Registry);
   initializeTailCallElimPass(Registry);
   initializeSeparateConstOffsetFromGEPPass(Registry);
-  initializeSpeculativeExecutionPass(Registry);
+  initializeSpeculativeExecutionLegacyPassPass(Registry);
   initializeStraightLineStrengthReducePass(Registry);
   initializeLoadCombinePass(Registry);
   initializePlaceBackedgeSafepointsImplPass(Registry);
   initializePlaceSafepointsPass(Registry);
   initializeFloat2IntLegacyPassPass(Registry);
   initializeLoopDistributeLegacyPass(Registry);
   initializeLoopLoadEliminationPass(Registry);
   initializeLoopSimplifyCFGLegacyPassPass(Registry);

llvm/trunk/lib/Transforms/Scalar/SpeculativeExecution.cpp

 // effect on targets where TargetTransformInfo::hasBranchDivergence() is true;
 // on other targets, it is a nop.
 //
 // This lets you include this pass unconditionally in the IR pass pipeline, but
 // only enable it for relevant targets.
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/Transforms/Scalar/SpeculativeExecution.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/Analysis/GlobalsModRef.h"
-#include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 
 using namespace llvm;

 static cl::opt<bool> SpecExecOnlyIfDivergentTarget(
     "spec-exec-only-if-divergent-target", cl::init(false), cl::Hidden,
     cl::desc("Speculative execution is applied only to targets with divergent "
              "branches, even if the pass was configured to apply only to all "
              "targets."));
 
 namespace {
 
-class SpeculativeExecution : public FunctionPass {
- public:
-   static char ID;
-   explicit SpeculativeExecution(bool OnlyIfDivergentTarget = false)
-       : FunctionPass(ID),
-         OnlyIfDivergentTarget(OnlyIfDivergentTarget ||
-                               SpecExecOnlyIfDivergentTarget) {}
+class SpeculativeExecutionLegacyPass : public FunctionPass {
+  explicit SpeculativeExecutionLegacyPass(bool OnlyIfDivergentTarget = false)
+      : FunctionPass(ID), OnlyIfDivergentTarget(OnlyIfDivergentTarget ||
+                                                SpecExecOnlyIfDivergentTarget),
+        Impl(OnlyIfDivergentTarget) {}
 
-   void getAnalysisUsage(AnalysisUsage &AU) const override;
-   bool runOnFunction(Function &F) override;
 
-   const char *getPassName() const override {
-     if (OnlyIfDivergentTarget)
-       return "Speculatively execute instructions if target has divergent "
-              "branches";
-     return "Speculatively execute instructions";
-   }
 
- private:
-  bool runOnBasicBlock(BasicBlock &B);
-  bool considerHoistingFromTo(BasicBlock &FromBlock, BasicBlock &ToBlock);
-
-  // If true, this pass is a nop unless the target architecture has branch
-  // divergence.
+  // Variable preserved purely for correct name printing.
   const bool OnlyIfDivergentTarget;
-  const TargetTransformInfo *TTI = nullptr;
+
+  SpeculativeExecutionPass Impl;
 };
 } // namespace
 
-char SpeculativeExecution::ID = 0;
-INITIALIZE_PASS_BEGIN(SpeculativeExecution, "speculative-execution",
+char SpeculativeExecutionLegacyPass::ID = 0;
+INITIALIZE_PASS_BEGIN(SpeculativeExecutionLegacyPass, "speculative-execution",
                       "Speculatively execute instructions", false, false)
 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
-INITIALIZE_PASS_END(SpeculativeExecution, "speculative-execution",
+INITIALIZE_PASS_END(SpeculativeExecutionLegacyPass, "speculative-execution",
                     "Speculatively execute instructions", false, false)
 
-void SpeculativeExecution::getAnalysisUsage(AnalysisUsage &AU) const {
+void SpeculativeExecutionLegacyPass::getAnalysisUsage(AnalysisUsage &AU) const {
   AU.addRequired<TargetTransformInfoWrapperPass>();
   AU.addPreserved<GlobalsAAWrapperPass>();
 }
 
-bool SpeculativeExecution::runOnFunction(Function &F) {
+bool SpeculativeExecutionLegacyPass::runOnFunction(Function &F) {
   if (skipFunction(F))
     return false;
 
-  TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
+  auto *TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
+  return Impl.runImpl(F, TTI);
+}
+
+namespace llvm {
+
+bool SpeculativeExecutionPass::runImpl(Function &F, TargetTransformInfo *TTI) {
   if (OnlyIfDivergentTarget && !TTI->hasBranchDivergence()) {
     DEBUG(dbgs() << "Not running SpeculativeExecution because "
                     "TTI->hasBranchDivergence() is false.\n");
     return false;
   }
 
+  this->TTI = TTI;
   bool Changed = false;
   for (auto& B : F) {
     Changed |= runOnBasicBlock(B);
   }
   return Changed;
 }
 
-bool SpeculativeExecution::runOnBasicBlock(BasicBlock &B) {
+bool SpeculativeExecutionPass::runOnBasicBlock(BasicBlock &B) {
   BranchInst *BI = dyn_cast<BranchInst>(B.getTerminator());
   if (BI == nullptr)
     return false;
 
   if (BI->getNumSuccessors() != 2)
     return false;
   BasicBlock &Succ0 = *BI->getSuccessor(0);
   BasicBlock &Succ1 = *BI->getSuccessor(1);
switch (Operator::getOpcode(I)) {
     case Instruction::SExt:
       return TTI.getUserCost(I);
 
     default:
       return UINT_MAX; // Disallow anything not whitelisted.
   }
 }
 
-bool SpeculativeExecution::considerHoistingFromTo(BasicBlock &FromBlock,
-                                                  BasicBlock &ToBlock) {
+bool SpeculativeExecutionPass::considerHoistingFromTo(
+    BasicBlock &FromBlock, BasicBlock &ToBlock) {
   SmallSet<const Instruction *, 8> NotHoisted;
   const auto AllPrecedingUsesFromBlockHoisted = [&NotHoisted](User *U) {
     for (Value* V : U->operand_values()) {
       if (Instruction *I = dyn_cast<Instruction>(V)) {
         if (NotHoisted.count(I) > 0)
           return false;
       }
     }
for (auto I = FromBlock.begin(); I != FromBlock.end();) {
     ++I;
     if (!NotHoisted.count(&*Current)) {
       Current->moveBefore(ToBlock.getTerminator());
     }
   }
   return true;
 }
 
-namespace llvm {
-
 FunctionPass *createSpeculativeExecutionPass() {
-  return new SpeculativeExecution();
+  return new SpeculativeExecutionLegacyPass();
 }
 
 FunctionPass *createSpeculativeExecutionIfHasBranchDivergencePass() {
-  return new SpeculativeExecution(/* OnlyIfDivergentTarget = */ true);
+  return new SpeculativeExecutionLegacyPass(/* OnlyIfDivergentTarget = */ true);
 }
 
+SpeculativeExecutionPass::SpeculativeExecutionPass(bool OnlyIfDivergentTarget)
+    : OnlyIfDivergentTarget(OnlyIfDivergentTarget ||
+                            SpecExecOnlyIfDivergentTarget) {}
+
+PreservedAnalyses SpeculativeExecutionPass::run(Function &F,
+                                                FunctionAnalysisManager &AM) {
+  auto *TTI = &AM.getResult<TargetIRAnalysis>(F);
+
+  bool Changed = runImpl(F, TTI);
+
+  if (!Changed)
+    return PreservedAnalyses::all();
+  PreservedAnalyses PA;
+  PA.preserve<GlobalsAA>();
+  return PA;
+}
 }  // namespace llvm

llvm/trunk/test/Transforms/SpeculativeExecution/spec.ll

 ; RUN: opt < %s -S -speculative-execution \
 ; RUN:   -spec-exec-max-speculation-cost 4 -spec-exec-max-not-hoisted 3 \
 ; RUN:   | FileCheck %s
+; RUN: opt < %s -S -passes='speculative-execution' \
+; RUN:   -spec-exec-max-speculation-cost 4 -spec-exec-max-not-hoisted 3 \
+; RUN:   | FileCheck %s
 
 target datalayout = "e-i64:64-v16:16-v32:32-n16:32:64"
 
 ; Hoist in if-then pattern.
 define void @ifThen() {
 ; CHECK-LABEL: @ifThen(
 ; CHECK: %x = add i32 2, 3
 ; CHECK: br i1 true