Merge pull request #35241 from atrick/canonical-ossa

Add a CanonicalOSSALifetime utility

Author: atrick

include/swift/Basic/Compiler.h

@@ -103,4 +103,29 @@
 #define SWIFT_CRASH_BUG_REPORT_MESSAGE \
   "Please " SWIFT_BUG_REPORT_MESSAGE_BASE " and the crash backtrace."
 
+// Conditionally exclude declarations or statements that are only needed for
+// assertions from release builds (NDEBUG) without cluttering the surrounding
+// code by #ifdefs.
+//
+// struct DoThings  {
+//   SWIFT_ASSERT_ONLY_DECL(unsigned verifyCount = 0);
+//   DoThings() {
+//     SWIFT_ASSERT_ONLY(verifyCount = getNumberOfThingsToDo());
+//   }
+//   void doThings() {
+//     do {
+//       // ... do each thing
+//       SWIFT_ASSERT_ONLY(--verifyCount);
+//     } while (!done());
+//     assert(verifyCount == 0 && "did not do everything");
+//   }
+// };
+#ifdef NDEBUG
+#define SWIFT_ASSERT_ONLY_DECL(X)
+#define SWIFT_ASSERT_ONLY(X) do { } while (false)
+#else
+#define SWIFT_ASSERT_ONLY_DECL(X) X
+#define SWIFT_ASSERT_ONLY(X) do { X; } while (false)
+#endif
+
 #endif // SWIFT_BASIC_COMPILER_H

include/swift/SILOptimizer/PassManager/Passes.def

@@ -123,7 +123,9 @@ PASS(ConstantEvaluableSubsetChecker, "test-constant-evaluable-subset",
 PASS(CopyForwarding, "copy-forwarding",
      "Copy Forwarding to Remove Redundant Copies")
 PASS(CopyPropagation, "copy-propagation",
-     "Copy propagation to Remove Redundant SSA Copies")
+     "Copy propagation to Remove Redundant SSA Copies, pruning debug info")
+PASS(MandatoryCopyPropagation, "mandatory-copy-propagation",
+     "Copy propagation to Remove Redundant SSA Copies, preserving debug info")
 PASS(COWOpts, "cow-opts",
      "Optimize COW operations")
 PASS(Differentiation, "differentiation",

include/swift/SILOptimizer/Utils/CanonicalOSSALifetime.h

@@ -0,0 +1,293 @@
+//===--- CanonicalOSSALifetime.h - Canonicalize OSSA lifetimes --*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+///
+/// Canonicalize the copies and destroys of a single owned or guaranteed OSSA
+/// value.
+///
+/// This top-level API rewrites the extended OSSA lifetime of a SILValue:
+///
+///     void canonicalizeValueLifetime(SILValue def, CanonicalOSSALifetime &)
+///
+/// The extended lifetime transitively includes the uses of `def` itself along
+/// with the uses of any copies of `def`. Canonicalization provably minimizes
+/// the OSSA lifetime and its copies by rewriting all copies and destroys. Only
+/// consusming uses that are not on the liveness boundary require a copy.
+///
+/// Example #1: Handle consuming and nonconsuming uses.
+///
+///     bb0(%arg : @owned $T, %addr : @trivial $*T):
+///       %copy = copy_value %arg : $T
+///       debug_value %copy : $T
+///       store %copy to [init] %addr : $*T
+///       debug_value %arg : $T
+///       debug_value_addr %addr : $*T
+///       destroy_value %arg : $T
+///
+/// Will be transformed to:
+///
+///     bb0(%arg : @owned $T, %addr : @trivial $*T):
+///       // The original copy is deleted.
+///       debug_value %arg : $T
+///       // A new copy_value is inserted before the consuming store.
+///       %copy = copy_value %arg : $T
+///       store %copy to [init] %addr : $*T
+///       // The non-consuming use now uses the original value.
+///       debug_value %arg : $T
+///       // A new destroy is inserted after the last use.
+///       destroy_value %arg : $T
+///       debug_value_addr %addr : $*T
+///       // The original destroy is deleted.
+///
+/// Example #2: Handle control flow.
+///
+///     bb0(%arg : @owned $T):
+///       cond_br %_, bb1, bb2
+///     bb1:
+///       br bb3
+///     bb2:
+///       debug_value %arg : $T
+///       %copy = copy_value %arg : $T
+///       destroy_value %copy : $T
+///       br bb3
+///     bb3:
+///       destroy_value %arg : $T
+///
+/// Will be transformed to:
+///
+///     bb0(%arg : @owned $T):
+///       cond_br %_, bb1, bb2
+///     bb1:
+///       destroy_value %arg : $T
+///       br bb3
+///     bb2:
+///       // The original copy is deleted.
+///       debug_value %arg : $T
+///       destroy_value %arg : $T
+///       br bb3
+///     bb2:
+///       // The original destroy is deleted.
+///
+/// FIXME: Canonicalization currently bails out if any uses of the def has
+/// OperandOwnership::PointerEscape. Once project_box is protected by a borrow
+/// scope and mark_dependence is associated with an end_dependence,
+/// canonicalization will work everywhere as intended. The intention is to keep
+/// the canonicalization algorithm as simple and robust, leaving the remaining
+/// performance opportunities contingent on fixing the SIL representation.
+///
+/// FIXME: Canonicalization currently fails to eliminate copies downstream of a
+/// ForwardingBorrow. Aggregates should be fixed to be Reborrow instead of
+/// ForwardingBorrow, then computeCanonicalLiveness() can be fixed to extend
+/// liveness through ForwardingBorrows.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_SILOPTIMIZER_UTILS_CANONICALOSSALIFETIME_H
+#define SWIFT_SILOPTIMIZER_UTILS_CANONICALOSSALIFETIME_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SetVector.h"
+#include "swift/SIL/SILInstruction.h"
+#include "swift/SILOptimizer/Utils/PrunedLiveness.h"
+
+namespace swift {
+
+/// Information about consumes on the extended-lifetime boundary. Consuming uses
+/// within the lifetime are not included--they will consume a copy after
+/// rewriting. For borrowed def values, the consumes do not include the end of
+/// the borrow scope, rather the consumes transitively include consumes of any
+/// owned copies of the borrowed value.
+///
+/// This result remains valid during copy rewriting. The only instructions
+/// referenced it contains are consumes that cannot be deleted.
+class CanonicalOSSAConsumeInfo {
+  /// Map blocks on the lifetime boundary to the last consuming instruction.
+  llvm::SmallDenseMap<SILBasicBlock *, SILInstruction *, 4> finalBlockConsumes;
+
+  /// Record any debug_value instructions found after a final consume.
+  SmallVector<DebugValueInst *, 8> debugAfterConsume;
+
+  /// For borrowed defs, track per-block copies of the borrowed value that only
+  /// have uses outside the borrow scope and will not be removed by
+  /// canonicalization. These copies are effectively distinct OSSA lifetimes
+  /// that should be canonicalized separately.
+  llvm::SmallDenseMap<SILBasicBlock *, CopyValueInst *, 4> persistentCopies;
+
+public:
+  bool hasUnclaimedConsumes() const { return !finalBlockConsumes.empty(); }
+
+  void clear() {
+    finalBlockConsumes.clear();
+    debugAfterConsume.clear();
+    persistentCopies.clear();
+  }
+
+  bool hasFinalConsumes() const { return !finalBlockConsumes.empty(); }
+
+  void recordFinalConsume(SILInstruction *inst) {
+    assert(!finalBlockConsumes.count(inst->getParent()));
+    finalBlockConsumes[inst->getParent()] = inst;
+  }
+
+  // Return true if this instruction is marked as a final consume point of the
+  // current def's live range. A consuming instruction can only be claimed once
+  // because instructions like `tuple` can consume the same value via multiple
+  // operands.
+  bool claimConsume(SILInstruction *inst) {
+    auto destroyPos = finalBlockConsumes.find(inst->getParent());
+    if (destroyPos != finalBlockConsumes.end() && destroyPos->second == inst) {
+      finalBlockConsumes.erase(destroyPos);
+      return true;
+    }
+    return false;
+  }
+
+  /// Record a debug_value that is known to be outside pruned liveness. Assumes
+  /// that instructions are only visited once.
+  void recordDebugAfterConsume(DebugValueInst *dvi) {
+    debugAfterConsume.push_back(dvi);
+  }
+
+  ArrayRef<DebugValueInst *> getDebugInstsAfterConsume() const {
+    return debugAfterConsume;
+  }
+
+  bool hasPersistentCopies() const { return !persistentCopies.empty(); }
+
+  bool isPersistentCopy(CopyValueInst *copy) const {
+    auto iter = persistentCopies.find(copy->getParent());
+    if (iter == persistentCopies.end()) {
+      return false;
+    }
+    return iter->second == copy;
+  }
+
+  SWIFT_ASSERT_ONLY_DECL(void dump() const LLVM_ATTRIBUTE_USED);
+};
+
+/// Canonicalize OSSA lifetimes.
+///
+/// Allows the allocation of analysis state to be reused across calls to
+/// canonicalizeValueLifetime().
+class CanonicalizeOSSALifetime {
+public:
+  /// Find the original definition of a potentially copied value.
+  static SILValue getCanonicalCopiedDef(SILValue v);
+
+private:
+  /// If true, then debug_value instructions outside of non-debug
+  /// liveness may be pruned during canonicalization.
+  bool pruneDebug;
+
+  /// Current copied def for which this state describes the liveness.
+  SILValue currentDef;
+
+  /// If an outer copy is created for uses outside the borrow scope
+  CopyValueInst *outerCopy = nullptr;
+
+  /// Cumulatively, have any instructions been modified by canonicalization?
+  bool changed = false;
+
+  /// Original points in the CFG where the current value's lifetime is consumed
+  /// or destroyed. For guaranteed values it remains empty. A backward walk from
+  /// these blocks must discover all uses on paths that lead to a return or
+  /// throw.
+  ///
+  /// These blocks are not necessarily in the pruned live blocks since
+  /// pruned liveness does not consider destroy_values.
+  SmallSetVector<SILBasicBlock *, 8> consumingBlocks;
+
+  /// Record all interesting debug_value instructions here rather then treating
+  /// them like a normal use. An interesting debug_value is one that may lie
+  /// outisde the pruned liveness at the time it is discovered.
+  llvm::SmallDenseSet<DebugValueInst *, 8> debugValues;
+
+  /// Reuse a general worklist for def-use traversal.
+  SmallSetVector<SILValue, 8> defUseWorklist;
+
+  /// Reuse a general worklist for CFG traversal.
+  SmallSetVector<SILBasicBlock *, 8> blockWorklist;
+
+  /// Pruned liveness for the extended live range including copies. For this
+  /// purpose, only consuming instructions are considered "lifetime
+  /// ending". end_borrows do not end a liverange that may include owned copies.
+  PrunedLiveness liveness;
+
+  /// Information about consuming instructions discovered in this caonical OSSA
+  /// lifetime.
+  CanonicalOSSAConsumeInfo consumes;
+
+public:
+  CanonicalizeOSSALifetime(bool pruneDebug) : pruneDebug(pruneDebug) {}
+
+  SILValue getCurrentDef() const { return currentDef; }
+
+  void initDef(SILValue def) {
+    assert(consumingBlocks.empty() && debugValues.empty() && liveness.empty());
+    consumes.clear();
+
+    currentDef = def;
+    outerCopy = nullptr;
+    liveness.initializeDefBlock(def->getParentBlock());
+  }
+
+  void clearLiveness() {
+    consumingBlocks.clear();
+    debugValues.clear();
+    liveness.clear();
+  }
+
+  bool hasChanged() const { return changed; }
+
+  void setChanged() { changed = true; }
+
+  SILValue createdOuterCopy() const { return outerCopy; }
+
+  /// Top-Level API: rewrites copies and destroys within \p def's extended
+  /// lifetime. \p lifetime caches transient analysis state across multiple
+  /// calls.
+  ///
+  /// Return false if the OSSA structure cannot be recognized (with a proper
+  /// OSSA representation this will always return true).
+  ///
+  /// Upon returning, isChanged() indicates, cumulatively, whether any SIL
+  /// changes were made.
+  ///
+  /// Upon returning, createdOuterCopy() indicates whether a new copy was
+  /// created for uses outside the borrow scope. To canonicalize the new outer
+  /// lifetime, call this API again on the value defined by the new copy.
+  bool canonicalizeValueLifetime(SILValue def);
+
+protected:
+  void recordDebugValue(DebugValueInst *dvi) {
+    debugValues.insert(dvi);
+  }
+
+  void recordConsumingUse(Operand *use) {
+    consumingBlocks.insert(use->getUser()->getParent());
+  }
+
+  bool computeBorrowLiveness();
+
+  void consolidateBorrowScope();
+
+  bool computeCanonicalLiveness();
+
+  void findOrInsertDestroyInBlock(SILBasicBlock *bb);
+
+  void findOrInsertDestroys();
+
+  void rewriteCopies();
+};
+
+} // end namespace swift
+
+#endif

include/swift/SILOptimizer/Utils/PrunedLiveness.h

@@ -90,14 +90,6 @@
 
 #include "swift/SIL/SILBasicBlock.h"
 
-#ifdef NDEBUG
-#define SWIFT_ASSERT_ONLY_MEMBER(X)
-#define SWIFT_ASSERT_ONLY(X) do { } while (false)
-#else
-#define SWIFT_ASSERT_ONLY_MEMBER(X) X
-#define SWIFT_ASSERT_ONLY(X) do { X; } while (false)
-#endif
-
 namespace swift {
 
 /// Discover "pruned" liveness for an arbitrary set of uses. The client builds
@@ -140,13 +132,15 @@ class PrunedLiveBlocks {
   llvm::SmallDenseMap<SILBasicBlock *, bool, 4> liveBlocks;
 
   // Once the first use has been seen, no definitions can be added.
-  SWIFT_ASSERT_ONLY_MEMBER(bool seenUse = false);
+  SWIFT_ASSERT_ONLY_DECL(bool seenUse = false);
 
 public:
   bool empty() const { return liveBlocks.empty(); }
 
   void clear() { liveBlocks.clear(); SWIFT_ASSERT_ONLY(seenUse = false); }
 
+  unsigned numLiveBlocks() const { return liveBlocks.size(); }
+
   void initializeDefBlock(SILBasicBlock *defBB) {
     assert(!seenUse && "cannot initialize more defs with partial liveness");
     markBlockLive(defBB, LiveWithin);
@@ -212,10 +206,17 @@ class PrunedLiveness {
     users.clear();
   }
 
+  unsigned numLiveBlocks() const { return liveBlocks.numLiveBlocks(); }
+
   void initializeDefBlock(SILBasicBlock *defBB) {
     liveBlocks.initializeDefBlock(defBB);
   }
 
+  /// For flexibility, \p lifetimeEnding is provided by the
+  /// caller. PrunedLiveness makes no assumptions about the def-use
+  /// relationships that generate liveness. For example, use->isLifetimeEnding()
+  /// cannot distinguish the end of the borrow scope that defines this extended
+  /// live range vs. a nested borrow scope within the extended live range.
   void updateForUse(Operand *use, bool lifetimeEnding);
 
   PrunedLiveBlocks::IsLive getBlockLiveness(SILBasicBlock *bb) const {