vendor/llvm-project/llvmorg-17-init-19304-gd0b54bb50e51

1 files changed, 231 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/MoveAutoInit.cpp b/llvm/lib/Transforms/Utils/MoveAutoInit.cpp
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index 000000000000..b0ca0b15c08e
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+++ b/llvm/lib/Transforms/Utils/MoveAutoInit.cpp
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+//===-- MoveAutoInit.cpp - move auto-init inst closer to their use site----===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass moves instruction maked as auto-init closer to the basic block that
+// use it, eventually removing it from some control path of the function.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/MoveAutoInit.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringSet.h"
+#include "llvm/Analysis/MemorySSA.h"
+#include "llvm/Analysis/MemorySSAUpdater.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/DebugInfo.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Transforms/Utils.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "move-auto-init"
+
+STATISTIC(NumMoved, "Number of instructions moved");
+
+static cl::opt<unsigned> MoveAutoInitThreshold(
+    "move-auto-init-threshold", cl::Hidden, cl::init(128),
+    cl::desc("Maximum instructions to analyze per moved initialization"));
+
+static bool hasAutoInitMetadata(const Instruction &I) {
+  return I.hasMetadata(LLVMContext::MD_annotation) &&
+         any_of(I.getMetadata(LLVMContext::MD_annotation)->operands(),
+                [](const MDOperand &Op) { return Op.equalsStr("auto-init"); });
+}
+
+static std::optional<MemoryLocation> writeToAlloca(const Instruction &I) {
+  MemoryLocation ML;
+  if (auto *MI = dyn_cast<MemIntrinsic>(&I))
+    ML = MemoryLocation::getForDest(MI);
+  else if (auto *SI = dyn_cast<StoreInst>(&I))
+    ML = MemoryLocation::get(SI);
+  else
+    assert(false && "memory location set");
+
+  if (isa<AllocaInst>(getUnderlyingObject(ML.Ptr)))
+    return ML;
+  else
+    return {};
+}
+
+/// Finds a BasicBlock in the CFG where instruction `I` can be moved to while
+/// not changing the Memory SSA ordering and being guarded by at least one
+/// condition.
+static BasicBlock *usersDominator(const MemoryLocation &ML, Instruction *I,
+                                  DominatorTree &DT, MemorySSA &MSSA) {
+  BasicBlock *CurrentDominator = nullptr;
+  MemoryUseOrDef &IMA = *MSSA.getMemoryAccess(I);
+  BatchAAResults AA(MSSA.getAA());
+
+  SmallPtrSet<MemoryAccess *, 8> Visited;
+
+  auto AsMemoryAccess = [](User *U) { return cast<MemoryAccess>(U); };
+  SmallVector<MemoryAccess *> WorkList(map_range(IMA.users(), AsMemoryAccess));
+
+  while (!WorkList.empty()) {
+    MemoryAccess *MA = WorkList.pop_back_val();
+    if (!Visited.insert(MA).second)
+      continue;
+
+    if (Visited.size() > MoveAutoInitThreshold)
+      return nullptr;
+
+    bool FoundClobberingUser = false;
+    if (auto *M = dyn_cast<MemoryUseOrDef>(MA)) {
+      Instruction *MI = M->getMemoryInst();
+
+      // If this memory instruction may not clobber `I`, we can skip it.
+      // LifetimeEnd is a valid user, but we do not want it in the user
+      // dominator.
+      if (AA.getModRefInfo(MI, ML) != ModRefInfo::NoModRef &&
+          !MI->isLifetimeStartOrEnd() && MI != I) {
+        FoundClobberingUser = true;
+        CurrentDominator = CurrentDominator
+                               ? DT.findNearestCommonDominator(CurrentDominator,
+                                                               MI->getParent())
+                               : MI->getParent();
+      }
+    }
+    if (!FoundClobberingUser) {
+      auto UsersAsMemoryAccesses = map_range(MA->users(), AsMemoryAccess);
+      append_range(WorkList, UsersAsMemoryAccesses);
+    }
+  }
+  return CurrentDominator;
+}
+
+static bool runMoveAutoInit(Function &F, DominatorTree &DT, MemorySSA &MSSA) {
+  BasicBlock &EntryBB = F.getEntryBlock();
+  SmallVector<std::pair<Instruction *, BasicBlock *>> JobList;
+
+  //
+  // Compute movable instructions.
+  //
+  for (Instruction &I : EntryBB) {
+    if (!hasAutoInitMetadata(I))
+      continue;
+
+    std::optional<MemoryLocation> ML = writeToAlloca(I);
+    if (!ML)
+      continue;
+
+    if (I.isVolatile())
+      continue;
+
+    BasicBlock *UsersDominator = usersDominator(ML.value(), &I, DT, MSSA);
+    if (!UsersDominator)
+      continue;
+
+    if (UsersDominator == &EntryBB)
+      continue;
+
+    // Traverse the CFG to detect cycles `UsersDominator` would be part of.
+    SmallPtrSet<BasicBlock *, 8> TransitiveSuccessors;
+    SmallVector<BasicBlock *> WorkList(successors(UsersDominator));
+    bool HasCycle = false;
+    while (!WorkList.empty()) {
+      BasicBlock *CurrBB = WorkList.pop_back_val();
+      if (CurrBB == UsersDominator)
+        // No early exit because we want to compute the full set of transitive
+        // successors.
+        HasCycle = true;
+      for (BasicBlock *Successor : successors(CurrBB)) {
+        if (!TransitiveSuccessors.insert(Successor).second)
+          continue;
+        WorkList.push_back(Successor);
+      }
+    }
+
+    // Don't insert if that could create multiple execution of I,
+    // but we can insert it in the non back-edge predecessors, if it exists.
+    if (HasCycle) {
+      BasicBlock *UsersDominatorHead = UsersDominator;
+      while (BasicBlock *UniquePredecessor =
+                 UsersDominatorHead->getUniquePredecessor())
+        UsersDominatorHead = UniquePredecessor;
+
+      if (UsersDominatorHead == &EntryBB)
+        continue;
+
+      BasicBlock *DominatingPredecessor = nullptr;
+      for (BasicBlock *Pred : predecessors(UsersDominatorHead)) {
+        // If one of the predecessor of the dominator also transitively is a
+        // successor, moving to the dominator would do the inverse of loop
+        // hoisting, and we don't want that.
+        if (TransitiveSuccessors.count(Pred))
+          continue;
+
+        DominatingPredecessor =
+            DominatingPredecessor
+                ? DT.findNearestCommonDominator(DominatingPredecessor, Pred)
+                : Pred;
+      }
+
+      if (!DominatingPredecessor || DominatingPredecessor == &EntryBB)
+        continue;
+
+      UsersDominator = DominatingPredecessor;
+    }
+
+    // CatchSwitchInst blocks can only have one instruction, so they are not
+    // good candidates for insertion.
+    while (isa<CatchSwitchInst>(UsersDominator->getFirstInsertionPt())) {
+      for (BasicBlock *Pred : predecessors(UsersDominator))
+        UsersDominator = DT.findNearestCommonDominator(UsersDominator, Pred);
+    }
+
+    // We finally found a place where I can be moved while not introducing extra
+    // execution, and guarded by at least one condition.
+    if (UsersDominator != &EntryBB)
+      JobList.emplace_back(&I, UsersDominator);
+  }
+
+  //
+  // Perform the actual substitution.
+  //
+  if (JobList.empty())
+    return false;
+
+  MemorySSAUpdater MSSAU(&MSSA);
+
+  // Reverse insertion to respect relative order between instructions:
+  // if two instructions are moved from the same BB to the same BB, we insert
+  // the second one in the front, then the first on top of it.
+  for (auto &Job : reverse(JobList)) {
+    Job.first->moveBefore(&*Job.second->getFirstInsertionPt());
+    MSSAU.moveToPlace(MSSA.getMemoryAccess(Job.first), Job.first->getParent(),
+                      MemorySSA::InsertionPlace::Beginning);
+  }
+
+  if (VerifyMemorySSA)
+    MSSA.verifyMemorySSA();
+
+  NumMoved += JobList.size();
+
+  return true;
+}
+
+PreservedAnalyses MoveAutoInitPass::run(Function &F,
+                                        FunctionAnalysisManager &AM) {
+
+  auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
+  auto &MSSA = AM.getResult<MemorySSAAnalysis>(F).getMSSA();
+  if (!runMoveAutoInit(F, DT, MSSA))
+    return PreservedAnalyses::all();
+
+  PreservedAnalyses PA;
+  PA.preserve<DominatorTreeAnalysis>();
+  PA.preserve<MemorySSAAnalysis>();
+  PA.preserveSet<CFGAnalyses>();
+  return PA;
+}