[PM] Port SpeculativeExecution to the new PM

Differential Revision: https://reviews.llvm.org/D23033

llvm-svn: 277393

llvm/include/llvm/InitializePasses.h

@@ -313,7 +313,7 @@ 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&);

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

@@ -0,0 +1,92 @@
+//===- 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/lib/Passes/PassBuilder.cpp

@@ -112,6 +112,7 @@
 #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"

llvm/lib/Passes/PassRegistry.def

@@ -175,6 +175,7 @@ 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())

llvm/lib/Transforms/Scalar/Scalar.cpp

@@ -80,7 +80,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializeSinkingLegacyPassPass(Registry);
   initializeTailCallElimPass(Registry);
   initializeSeparateConstOffsetFromGEPPass(Registry);
-  initializeSpeculativeExecutionPass(Registry);
+  initializeSpeculativeExecutionLegacyPassPass(Registry);
   initializeStraightLineStrengthReducePass(Registry);
   initializeLoadCombinePass(Registry);
   initializePlaceBackedgeSafepointsImplPass(Registry);

llvm/lib/Transforms/Scalar/SpeculativeExecution.cpp

@@ -61,9 +61,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#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"
@@ -101,58 +101,62 @@ static cl::opt<bool> SpecExecOnlyIfDivergentTarget(
 
 namespace {
 
-class SpeculativeExecution : public FunctionPass {
- public:
-   static char ID;
-   explicit SpeculativeExecution(bool OnlyIfDivergentTarget = false)
-       : FunctionPass(ID),
-         OnlyIfDivergentTarget(OnlyIfDivergentTarget ||
-                               SpecExecOnlyIfDivergentTarget) {}
+class SpeculativeExecutionLegacyPass : public FunctionPass {
+public:
+  static char ID;
+  explicit SpeculativeExecutionLegacyPass(bool OnlyIfDivergentTarget = false)
+      : FunctionPass(ID), OnlyIfDivergentTarget(OnlyIfDivergentTarget ||
+                                                SpecExecOnlyIfDivergentTarget),
+        Impl(OnlyIfDivergentTarget) {}
 
-   void getAnalysisUsage(AnalysisUsage &AU) const override;
-   bool runOnFunction(Function &F) override;
+  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";
-   }
+  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.
+private:
+  // 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);
@@ -160,7 +164,7 @@ bool SpeculativeExecution::runOnFunction(Function &F) {
   return Changed;
 }
 
-bool SpeculativeExecution::runOnBasicBlock(BasicBlock &B) {
+bool SpeculativeExecutionPass::runOnBasicBlock(BasicBlock &B) {
   BranchInst *BI = dyn_cast<BranchInst>(B.getTerminator());
   if (BI == nullptr)
     return false;
@@ -227,8 +231,8 @@ static unsigned ComputeSpeculationCost(const Instruction *I,
   }
 }
 
-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()) {
@@ -270,14 +274,28 @@ bool SpeculativeExecution::considerHoistingFromTo(BasicBlock &FromBlock,
   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/test/Transforms/SpeculativeExecution/spec.ll

@@ -1,6 +1,9 @@
 ; 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"