[MemorySSA] Remove -enable-mssa-loop-dependency option

This option has been enabled by default for quite a while now.
The practical impact of removing the option is that MSSA use
cannot be disabled in default pipelines (both LPM and NPM) and
in manual LPM invocations. NPM can still choose to enable/disable
MSSA using loop vs loop-mssa.

The next step will be to require MSSA for LICM and drop the
AST-based implementation entirely.

Differential Revision: https://reviews.llvm.org/D108075

llvm/include/llvm/Analysis/MemorySSA.h

@@ -106,9 +106,6 @@
 
 namespace llvm {
 
-/// Enables memory ssa as a dependency for loop passes.
-extern cl::opt<bool> EnableMSSALoopDependency;
-
 class AllocaInst;
 class Function;
 class Instruction;

llvm/lib/Analysis/MemorySSA.cpp

@@ -90,10 +90,6 @@ bool llvm::VerifyMemorySSA = true;
 #else
 bool llvm::VerifyMemorySSA = false;
 #endif
-/// Enables memory ssa as a dependency for loop passes in legacy pass manager.
-cl::opt<bool> llvm::EnableMSSALoopDependency(
-    "enable-mssa-loop-dependency", cl::Hidden, cl::init(true),
-    cl::desc("Enable MemorySSA dependency for loop pass manager"));
 
 static cl::opt<bool, true>
     VerifyMemorySSAX("verify-memoryssa", cl::location(VerifyMemorySSA),

llvm/lib/Passes/PassBuilder.cpp

@@ -617,7 +617,7 @@ PassBuilder::buildO1FunctionSimplificationPipeline(OptimizationLevel Level,
   FPM.addPass(
       RequireAnalysisPass<OptimizationRemarkEmitterAnalysis, Function>());
   FPM.addPass(createFunctionToLoopPassAdaptor(std::move(LPM1),
-                                              EnableMSSALoopDependency,
+                                              /*UseMemorySSA=*/true,
                                               /*UseBlockFrequencyInfo=*/true));
   FPM.addPass(SimplifyCFGPass());
   FPM.addPass(InstCombinePass());
@@ -791,7 +791,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
   FPM.addPass(
       RequireAnalysisPass<OptimizationRemarkEmitterAnalysis, Function>());
   FPM.addPass(createFunctionToLoopPassAdaptor(std::move(LPM1),
-                                              EnableMSSALoopDependency,
+                                              /*UseMemorySSA=*/true,
                                               /*UseBlockFrequencyInfo=*/true));
   FPM.addPass(SimplifyCFGPass());
   FPM.addPass(InstCombinePass());
@@ -848,7 +848,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
   FPM.addPass(DSEPass());
   FPM.addPass(createFunctionToLoopPassAdaptor(
       LICMPass(PTO.LicmMssaOptCap, PTO.LicmMssaNoAccForPromotionCap),
-      EnableMSSALoopDependency, /*UseBlockFrequencyInfo=*/true));
+      /*UseMemorySSA=*/true, /*UseBlockFrequencyInfo=*/true));
 
   FPM.addPass(CoroElidePass());
 
@@ -1246,9 +1246,9 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
                                        OptimizationLevel::O3));
     FPM.addPass(
         RequireAnalysisPass<OptimizationRemarkEmitterAnalysis, Function>());
-    FPM.addPass(createFunctionToLoopPassAdaptor(
-        std::move(LPM), EnableMSSALoopDependency,
-        /*UseBlockFrequencyInfo=*/true));
+    FPM.addPass(
+        createFunctionToLoopPassAdaptor(std::move(LPM), /*UseMemorySSA=*/true,
+                                        /*UseBlockFrequencyInfo=*/true));
     FPM.addPass(SimplifyCFGPass());
     FPM.addPass(InstCombinePass());
   }
@@ -1307,7 +1307,7 @@ void PassBuilder::addVectorPasses(OptimizationLevel Level,
         RequireAnalysisPass<OptimizationRemarkEmitterAnalysis, Function>());
     FPM.addPass(createFunctionToLoopPassAdaptor(
         LICMPass(PTO.LicmMssaOptCap, PTO.LicmMssaNoAccForPromotionCap),
-        EnableMSSALoopDependency, /*UseBlockFrequencyInfo=*/true));
+        /*UseMemorySSA=*/true, /*UseBlockFrequencyInfo=*/true));
   }
 
   // Now that we've vectorized and unrolled loops, we may have more refined
@@ -1828,7 +1828,7 @@ PassBuilder::buildLTODefaultPipeline(OptimizationLevel Level,
   FunctionPassManager MainFPM;
   MainFPM.addPass(createFunctionToLoopPassAdaptor(
       LICMPass(PTO.LicmMssaOptCap, PTO.LicmMssaNoAccForPromotionCap),
-      EnableMSSALoopDependency, /*UseBlockFrequencyInfo=*/true));
+      /*USeMemorySSA=*/true, /*UseBlockFrequencyInfo=*/true));
 
   if (RunNewGVN)
     MainFPM.addPass(NewGVNPass());

llvm/lib/Transforms/Scalar/LICM.cpp

@@ -229,9 +229,7 @@ struct LegacyLICMPass : public LoopPass {
                       << L->getHeader()->getNameOrAsOperand() << "\n");
 
     auto *SE = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
-    MemorySSA *MSSA = EnableMSSALoopDependency
-                          ? (&getAnalysis<MemorySSAWrapperPass>().getMSSA())
-                          : nullptr;
+    MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
     bool hasProfileData = L->getHeader()->getParent()->hasProfileData();
     BlockFrequencyInfo *BFI =
         hasProfileData ? &getAnalysis<LazyBlockFrequencyInfoPass>().getBFI()
@@ -258,10 +256,8 @@ struct LegacyLICMPass : public LoopPass {
     AU.addPreserved<DominatorTreeWrapperPass>();
     AU.addPreserved<LoopInfoWrapperPass>();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
-    if (EnableMSSALoopDependency) {
-      AU.addRequired<MemorySSAWrapperPass>();
-      AU.addPreserved<MemorySSAWrapperPass>();
-    }
+    AU.addRequired<MemorySSAWrapperPass>();
+    AU.addPreserved<MemorySSAWrapperPass>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
     getLoopAnalysisUsage(AU);
     LazyBlockFrequencyInfoPass::getLazyBFIAnalysisUsage(AU);

llvm/lib/Transforms/Scalar/LoopInstSimplify.cpp

@@ -195,26 +195,19 @@ class LoopInstSimplifyLegacyPass : public LoopPass {
     const TargetLibraryInfo &TLI =
         getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(
             *L->getHeader()->getParent());
-    MemorySSA *MSSA = nullptr;
-    Optional<MemorySSAUpdater> MSSAU;
-    if (EnableMSSALoopDependency) {
-      MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
-      MSSAU = MemorySSAUpdater(MSSA);
-    }
+    MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
+    MemorySSAUpdater MSSAU(MSSA);
 
-    return simplifyLoopInst(*L, DT, LI, AC, TLI,
-                            MSSAU.hasValue() ? MSSAU.getPointer() : nullptr);
+    return simplifyLoopInst(*L, DT, LI, AC, TLI, &MSSAU);
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<AssumptionCacheTracker>();
     AU.addRequired<DominatorTreeWrapperPass>();
     AU.addRequired<TargetLibraryInfoWrapperPass>();
     AU.setPreservesCFG();
-    if (EnableMSSALoopDependency) {
-      AU.addRequired<MemorySSAWrapperPass>();
-      AU.addPreserved<MemorySSAWrapperPass>();
-    }
+    AU.addRequired<MemorySSAWrapperPass>();
+    AU.addPreserved<MemorySSAWrapperPass>();
     getLoopAnalysisUsage(AU);
   }
 };

llvm/lib/Transforms/Scalar/LoopRotation.cpp

@@ -99,8 +99,7 @@ class LoopRotateLegacyPass : public LoopPass {
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<AssumptionCacheTracker>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
-    if (EnableMSSALoopDependency)
-      AU.addPreserved<MemorySSAWrapperPass>();
+    AU.addPreserved<MemorySSAWrapperPass>();
     getLoopAnalysisUsage(AU);
 
     // Lazy BFI and BPI are marked as preserved here so LoopRotate
@@ -121,13 +120,11 @@ class LoopRotateLegacyPass : public LoopPass {
     auto &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
     const SimplifyQuery SQ = getBestSimplifyQuery(*this, F);
     Optional<MemorySSAUpdater> MSSAU;
-    if (EnableMSSALoopDependency) {
-      // Not requiring MemorySSA and getting it only if available will split
-      // the loop pass pipeline when LoopRotate is being run first.
-      auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
-      if (MSSAA)
-        MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
-    }
+    // Not requiring MemorySSA and getting it only if available will split
+    // the loop pass pipeline when LoopRotate is being run first.
+    auto *MSSAA = getAnalysisIfAvailable<MemorySSAWrapperPass>();
+    if (MSSAA)
+      MSSAU = MemorySSAUpdater(&MSSAA->getMSSA());
     // Vectorization requires loop-rotation. Use default threshold for loops the
     // user explicitly marked for vectorization, even when header duplication is
     // disabled.

llvm/lib/Transforms/Scalar/LoopSimplifyCFG.cpp

@@ -733,27 +733,20 @@ class LoopSimplifyCFGLegacyPass : public LoopPass {
     DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
     LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
     ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
-    Optional<MemorySSAUpdater> MSSAU;
-    if (EnableMSSALoopDependency) {
-      MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
-      MSSAU = MemorySSAUpdater(MSSA);
-      if (VerifyMemorySSA)
-        MSSA->verifyMemorySSA();
-    }
+    MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
+    MemorySSAUpdater MSSAU(MSSA);
+    if (VerifyMemorySSA)
+      MSSA->verifyMemorySSA();
     bool DeleteCurrentLoop = false;
-    bool Changed = simplifyLoopCFG(
-        *L, DT, LI, SE, MSSAU.hasValue() ? MSSAU.getPointer() : nullptr,
-        DeleteCurrentLoop);
+    bool Changed = simplifyLoopCFG(*L, DT, LI, SE, &MSSAU, DeleteCurrentLoop);
     if (DeleteCurrentLoop)
       LPM.markLoopAsDeleted(*L);
     return Changed;
   }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
-    if (EnableMSSALoopDependency) {
-      AU.addRequired<MemorySSAWrapperPass>();
-      AU.addPreserved<MemorySSAWrapperPass>();
-    }
+    AU.addRequired<MemorySSAWrapperPass>();
+    AU.addPreserved<MemorySSAWrapperPass>();
     AU.addPreserved<DependenceAnalysisWrapperPass>();
     getLoopAnalysisUsage(AU);
   }

llvm/lib/Transforms/Scalar/LoopUnswitch.cpp

@@ -232,10 +232,8 @@ namespace {
       AU.addPreserved<LazyBranchProbabilityInfoPass>();
       AU.addRequired<AssumptionCacheTracker>();
       AU.addRequired<TargetTransformInfoWrapperPass>();
-      if (EnableMSSALoopDependency) {
-        AU.addRequired<MemorySSAWrapperPass>();
-        AU.addPreserved<MemorySSAWrapperPass>();
-      }
+      AU.addRequired<MemorySSAWrapperPass>();
+      AU.addPreserved<MemorySSAWrapperPass>();
       if (HasBranchDivergence)
         AU.addRequired<LegacyDivergenceAnalysis>();
       getLoopAnalysisUsage(AU);
@@ -539,31 +537,28 @@ bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPMRef) {
   LPM = &LPMRef;
   DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
   AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
-  if (EnableMSSALoopDependency) {
-    MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
-    MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
-    assert(DT && "Cannot update MemorySSA without a valid DomTree.");
-  }
+  MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
+  MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
   CurrentLoop = L;
   Function *F = CurrentLoop->getHeader()->getParent();
 
   SanitizeMemory = F->hasFnAttribute(Attribute::SanitizeMemory);
   if (SanitizeMemory)
     SafetyInfo.computeLoopSafetyInfo(L);
 
-  if (MSSA && VerifyMemorySSA)
+  if (VerifyMemorySSA)
     MSSA->verifyMemorySSA();
 
   bool Changed = false;
   do {
     assert(CurrentLoop->isLCSSAForm(*DT));
-    if (MSSA && VerifyMemorySSA)
+    if (VerifyMemorySSA)
       MSSA->verifyMemorySSA();
     RedoLoop = false;
     Changed |= processCurrentLoop();
   } while (RedoLoop);
 
-  if (MSSA && VerifyMemorySSA)
+  if (VerifyMemorySSA)
     MSSA->verifyMemorySSA();
 
   return Changed;

llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp

@@ -3126,10 +3126,8 @@ class SimpleLoopUnswitchLegacyPass : public LoopPass {
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<AssumptionCacheTracker>();
     AU.addRequired<TargetTransformInfoWrapperPass>();
-    if (EnableMSSALoopDependency) {
-      AU.addRequired<MemorySSAWrapperPass>();
-      AU.addPreserved<MemorySSAWrapperPass>();
-    }
+    AU.addRequired<MemorySSAWrapperPass>();
+    AU.addPreserved<MemorySSAWrapperPass>();
     getLoopAnalysisUsage(AU);
   }
 };
@@ -3150,12 +3148,8 @@ bool SimpleLoopUnswitchLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
   auto &AC = getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
   auto &AA = getAnalysis<AAResultsWrapperPass>().getAAResults();
   auto &TTI = getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
-  MemorySSA *MSSA = nullptr;
-  Optional<MemorySSAUpdater> MSSAU;
-  if (EnableMSSALoopDependency) {
-    MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
-    MSSAU = MemorySSAUpdater(MSSA);
-  }
+  MemorySSA *MSSA = &getAnalysis<MemorySSAWrapperPass>().getMSSA();
+  MemorySSAUpdater MSSAU(MSSA);
 
   auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
   auto *SE = SEWP ? &SEWP->getSE() : nullptr;
@@ -3179,14 +3173,13 @@ bool SimpleLoopUnswitchLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
       LPM.markLoopAsDeleted(*L);
   };
 
-  if (MSSA && VerifyMemorySSA)
+  if (VerifyMemorySSA)
     MSSA->verifyMemorySSA();
 
-  bool Changed =
-      unswitchLoop(*L, DT, LI, AC, AA, TTI, true, NonTrivial, UnswitchCB, SE,
-                   MSSAU.hasValue() ? MSSAU.getPointer() : nullptr);
+  bool Changed = unswitchLoop(*L, DT, LI, AC, AA, TTI, true, NonTrivial,
+                              UnswitchCB, SE, &MSSAU);
 
-  if (MSSA && VerifyMemorySSA)
+  if (VerifyMemorySSA)
     MSSA->verifyMemorySSA();
 
   // Historically this pass has had issues with the dominator tree so verify it

llvm/lib/Transforms/Utils/LoopSimplify.cpp

@@ -779,8 +779,7 @@ namespace {
       AU.addPreserved<DependenceAnalysisWrapperPass>();
       AU.addPreservedID(BreakCriticalEdgesID);  // No critical edges added.
       AU.addPreserved<BranchProbabilityInfoWrapperPass>();
-      if (EnableMSSALoopDependency)
-        AU.addPreserved<MemorySSAWrapperPass>();
+      AU.addPreserved<MemorySSAWrapperPass>();
     }
 
     /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
@@ -814,12 +813,10 @@ bool LoopSimplify::runOnFunction(Function &F) {
       &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
   MemorySSA *MSSA = nullptr;
   std::unique_ptr<MemorySSAUpdater> MSSAU;
-  if (EnableMSSALoopDependency) {
-    auto *MSSAAnalysis = getAnalysisIfAvailable<MemorySSAWrapperPass>();
-    if (MSSAAnalysis) {
-      MSSA = &MSSAAnalysis->getMSSA();
-      MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
-    }
+  auto *MSSAAnalysis = getAnalysisIfAvailable<MemorySSAWrapperPass>();
+  if (MSSAAnalysis) {
+    MSSA = &MSSAAnalysis->getMSSA();
+    MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
   }
 
   bool PreserveLCSSA = mustPreserveAnalysisID(LCSSAID);

llvm/test/Analysis/BasicAA/store-promote.ll

@@ -2,7 +2,6 @@
 ; disambiguating some obvious cases.  If LICM is able to disambiguate the
 ; two pointers, then the load should be hoisted, and the store sunk.
 
-; RUN: opt < %s -basic-aa -licm -enable-mssa-loop-dependency=false -enable-new-pm=0 -S | FileCheck %s -check-prefixes=CHECK,AST
 ; RUN: opt < %s -basic-aa -licm -enable-new-pm=0 -S | FileCheck %s -check-prefixes=CHECK,MSSA
 ; RUN: opt < %s -aa-pipeline=basic-aa -passes='loop(licm)' -S | FileCheck %s -check-prefixes=CHECK,AST
 ; RUN: opt < %s -aa-pipeline=basic-aa -passes='loop-mssa(licm)' -S | FileCheck %s -check-prefixes=CHECK,MSSA

llvm/test/Analysis/MemorySSA/pr42294.ll

@@ -1,8 +1,6 @@
 ; REQUIRES: asserts
 ; RUN: opt -loop-rotate -licm %s -disable-output -debug-only=licm 2>&1 | FileCheck %s -check-prefix=LICM
-; RUN: opt -loop-rotate -licm %s -disable-output -enable-mssa-loop-dependency=false -debug-only=licm 2>&1 | FileCheck %s -check-prefix=LICM
 ; RUN: opt -loop-rotate -licm %s -S  | FileCheck %s
-; RUN: opt -loop-rotate -licm %s -S -enable-mssa-loop-dependency=false | FileCheck %s
 
 ; LICM: Using
 ; LICM-NOT: LICM sinking instruction:   %.pre = load i8, i8* %arrayidx.phi.trans.insert

llvm/test/CodeGen/PowerPC/pr35688.ll

@@ -1,45 +1,26 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc -enable-mssa-loop-dependency=false -verify-machineinstrs -mtriple=powerpc64le-unknown-unknown < %s  | \
-; RUN:   FileCheck %s
 ; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-unknown < %s  | \
-; RUN:   FileCheck %s --check-prefix=MSSA
-; Function Attrs: nounwind
+; RUN:   FileCheck %s
+
+; With MemorySSA, everything is taken out of the loop by licm.
+; Loads and stores to undef are treated as non-aliasing.
 define void @ec_GFp_nistp256_points_mul() {
 ; CHECK-LABEL: ec_GFp_nistp256_points_mul:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    ld 5, 0(3)
-; CHECK-NEXT:    li 3, 127
+; CHECK-NEXT:    ld 3, 0(3)
 ; CHECK-NEXT:    li 4, 0
-; CHECK-NEXT:    .p2align 5
+; CHECK-NEXT:    subfic 5, 3, 0
+; CHECK-NEXT:    subfze 5, 4
+; CHECK-NEXT:    sradi 5, 5, 63
+; CHECK-NEXT:    subc 3, 5, 3
+; CHECK-NEXT:    subfe 3, 4, 5
+; CHECK-NEXT:    sradi 3, 3, 63
+; CHECK-NEXT:    std 3, 0(3)
+; CHECK-NEXT:    .p2align 4
 ; CHECK-NEXT:  .LBB0_1: # %fe_cmovznz.exit.i534.i.15
 ; CHECK-NEXT:    #
-; CHECK-NEXT:    subfic 6, 5, 0
-; CHECK-NEXT:    subfze 6, 4
-; CHECK-NEXT:    sradi 7, 6, 63
-; CHECK-NEXT:    srad 6, 6, 3
-; CHECK-NEXT:    subc 5, 7, 5
-; CHECK-NEXT:    subfe 5, 4, 6
-; CHECK-NEXT:    sradi 5, 5, 63
 ; CHECK-NEXT:    b .LBB0_1
-;
-; MSSA-LABEL: ec_GFp_nistp256_points_mul:
-; MSSA:       # %bb.0: # %entry
-; MSSA-NEXT:    ld 3, 0(3)
-; MSSA-NEXT:    li 4, 0
-; MSSA-NEXT:    subfic 5, 3, 0
-; MSSA-NEXT:    subfze 5, 4
-; MSSA-NEXT:    sradi 5, 5, 63
-; MSSA-NEXT:    subc 3, 5, 3
-; MSSA-NEXT:    subfe 3, 4, 5
-; MSSA-NEXT:    sradi 3, 3, 63
-; MSSA-NEXT:    std 3, 0(3)
-; MSSA-NEXT:    .p2align 4
-; MSSA-NEXT:  .LBB0_1: # %fe_cmovznz.exit.i534.i.15
-; MSSA-NEXT:    #
-; MSSA-NEXT:    b .LBB0_1
 
-; With MemorySSA, everything is taken out of the loop by licm.
-; Loads and stores to undef are treated as non-aliasing.
 entry:
   br label %fe_cmovznz.exit.i534.i.15