SILOptimizer: fix a phase ordering problem, which prevented array optimizations to work in some cases

include/swift/SILOptimizer/PassManager/Passes.def

@@ -154,6 +154,8 @@ PASS(ARCSequenceOpts, "arc-sequence-opts",
      "ARC Sequence Optimization")
 PASS(ARCLoopOpts, "arc-loop-opts",
      "ARC Loop Optimization")
+PASS(EarlyRedundantLoadElimination, "early-redundant-load-elim",
+     "Early Redundant Load Elimination")
 PASS(RedundantLoadElimination, "redundant-load-elim",
      "Redundant Load Elimination")
 PASS(DeadStoreElimination, "dead-store-elim",

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -305,7 +305,14 @@ void addSSAPasses(SILPassPipelinePlan &P, OptimizationLevelKind OpLevel) {
   P.addSimplifyCFG();
 
   P.addCSE();
-  P.addRedundantLoadElimination();
+  if (OpLevel == OptimizationLevelKind::HighLevel) {
+    // Early RLE does not touch loads from Arrays. This is important because
+    // later array optimizations, like ABCOpt, get confused if an array load in
+    // a loop is converted to a pattern with a phi argument.
+    P.addEarlyRedundantLoadElimination();
+  } else {
+    P.addRedundantLoadElimination();
+  }
 
   P.addPerformanceConstantPropagation();
   P.addCSE();

lib/SILOptimizer/Transforms/RedundantLoadElimination.cpp

@@ -481,14 +481,17 @@ class RLEContext {
   /// walked, i.e. when the we generate the genset and killset.
   llvm::DenseSet<SILBasicBlock *> BBWithLoads;
 
+  /// If set, RLE ignores loads from that array type.
+  NominalTypeDecl *ArrayType;
+
 #ifndef NDEBUG
   SILPrintContext printCtx;
 #endif
 
 public:
   RLEContext(SILFunction *F, SILPassManager *PM, AliasAnalysis *AA,
              TypeExpansionAnalysis *TE, PostOrderFunctionInfo *PO,
-             EpilogueARCFunctionInfo *EAFI);
+             EpilogueARCFunctionInfo *EAFI, bool disableArrayLoads);
 
   RLEContext(const RLEContext &) = delete;
   RLEContext(RLEContext &&) = default;
@@ -555,6 +558,17 @@ class RLEContext {
   /// Transitively collect all the values that make up this location and
   /// create a SILArgument out of them.
   SILValue computePredecessorLocationValue(SILBasicBlock *BB, LSLocation &L);
+
+  /// Returns the LoadInst if \p Inst is a load inst we want to handle.
+  LoadInst *isLoadInstToHandle(SILInstruction *Inst) {
+    if (auto *LI = dyn_cast<LoadInst>(Inst)) {
+      if (!ArrayType ||
+          LI->getType().getNominalOrBoundGenericNominal() != ArrayType) {
+        return LI;
+      }
+    }
+    return nullptr;
+  }
 };
 
 } // end anonymous namespace
@@ -1054,7 +1068,7 @@ void BlockState::processInstructionWithKind(RLEContext &Ctx,
 
   // This is a LoadInst. Let's see if we can find a previous loaded, stored
   // value to use instead of this load.
-  if (auto *LI = dyn_cast<LoadInst>(Inst)) {
+  if (auto *LI = Ctx.isLoadInstToHandle(Inst)) {
     processLoadInst(Ctx, LI, Kind);
     return;
   }
@@ -1174,8 +1188,10 @@ void BlockState::dump(RLEContext &Ctx) {
 
 RLEContext::RLEContext(SILFunction *F, SILPassManager *PM, AliasAnalysis *AA,
                        TypeExpansionAnalysis *TE, PostOrderFunctionInfo *PO,
-                       EpilogueARCFunctionInfo *EAFI)
-    : Fn(F), PM(PM), AA(AA), TE(TE), PO(PO), EAFI(EAFI)
+                       EpilogueARCFunctionInfo *EAFI, bool disableArrayLoads)
+    : Fn(F), PM(PM), AA(AA), TE(TE), PO(PO), EAFI(EAFI),
+      ArrayType(disableArrayLoads ?
+                F->getModule().getASTContext().getArrayDecl() : nullptr)
 #ifndef NDEBUG
       ,
       printCtx(llvm::dbgs(), /*Verbose=*/false, /*Sorted=*/true)
@@ -1612,6 +1628,14 @@ namespace {
 
 class RedundantLoadElimination : public SILFunctionTransform {
 
+private:
+  bool disableArrayLoads;
+
+public:
+
+  RedundantLoadElimination(bool disableArrayLoads)
+    : disableArrayLoads(disableArrayLoads) { }
+
   /// The entry point to the transformation.
   void run() override {
     SILFunction *F = getFunction();
@@ -1623,7 +1647,7 @@ class RedundantLoadElimination : public SILFunctionTransform {
     auto *PO = PM->getAnalysis<PostOrderAnalysis>()->get(F);
     auto *EAFI = PM->getAnalysis<EpilogueARCAnalysis>()->get(F);
 
-    RLEContext RLE(F, PM, AA, TE, PO, EAFI);
+    RLEContext RLE(F, PM, AA, TE, PO, EAFI, disableArrayLoads);
     if (RLE.run()) {
       invalidateAnalysis(SILAnalysis::InvalidationKind::Instructions);
     }
@@ -1632,6 +1656,10 @@ class RedundantLoadElimination : public SILFunctionTransform {
 
 } // end anonymous namespace
 
+SILTransform *swift::createEarlyRedundantLoadElimination() {
+  return new RedundantLoadElimination(/*disableArrayLoads=*/true);
+}
+
 SILTransform *swift::createRedundantLoadElimination() {
-  return new RedundantLoadElimination();
+  return new RedundantLoadElimination(/*disableArrayLoads=*/false);
 }

test/SILOptimizer/early-rle.sil

@@ -0,0 +1,36 @@
+// RUN: %target-sil-opt -assume-parsing-unqualified-ownership-sil -enable-sil-verify-all %s -early-redundant-load-elim | %FileCheck %s
+
+sil_stage canonical
+
+import Builtin
+import Swift
+import SwiftShims
+
+
+// Check that earlyl redundant load elimination ignores arrays.
+
+
+// CHECK-LABEL: test_array
+// CHECK: %1 = load
+// CHECK: %2 = load
+// CHECK: %3 = tuple (%1 {{.*}}, %2 {{.*}})
+sil @test_array : $@convention(thin) (@inout Array<Int>) -> (Array<Int>, Array<Int>) {
+bb0(%0 : $*Array<Int>):
+  %1 = load %0 : $*Array<Int>
+  %2 = load %0 : $*Array<Int>
+  %3 = tuple (%1: $Array<Int>, %2: $Array<Int>)
+  return %3 : $(Array<Int>, Array<Int>)
+}
+
+// CHECK-LABEL: test_non_array
+// CHECK: %1 = load
+// CHECK: %2 = tuple (%1 {{.*}}, %1 {{.*}})
+sil @test_non_array : $@convention(thin) (@inout Int) -> (Int, Int) {
+bb0(%0 : $*Int):
+  %1 = load %0 : $*Int
+  %2 = load %0 : $*Int
+  %3 = tuple (%1: $Int, %2: $Int)
+  return %3 : $(Int, Int)
+}
+
+