Reapply "[GVN] MemorySSA for GVN: add optional AllowMemorySSA"

Original commit: eb63cd6

Previously reverted due to non-negligible compile-time impact in
stage1-ReleaseLTO-g scenario. The issue has been addressed by
always reusing previously computed MemorySSA results, and request
new ones only when `isMemorySSAEnabled` is set.

Co-authored-by: Momchil Velikov <[email protected]>

Author: antoniofrighetto

llvm/include/llvm/Transforms/Scalar/GVN.h

@@ -77,6 +77,7 @@ struct GVNOptions {
   std::optional<bool> AllowLoadInLoopPRE;
   std::optional<bool> AllowLoadPRESplitBackedge;
   std::optional<bool> AllowMemDep;
+  std::optional<bool> AllowMemorySSA;
 
   GVNOptions() = default;
 
@@ -108,6 +109,12 @@ struct GVNOptions {
     AllowMemDep = MemDep;
     return *this;
   }
+
+  /// Enables or disables use of MemorySSA.
+  GVNOptions &setMemorySSA(bool MemSSA) {
+    AllowMemorySSA = MemSSA;
+    return *this;
+  }
 };
 
 /// The core GVN pass object.
@@ -144,6 +151,7 @@ class GVNPass : public PassInfoMixin<GVNPass> {
   bool isLoadInLoopPREEnabled() const;
   bool isLoadPRESplitBackedgeEnabled() const;
   bool isMemDepEnabled() const;
+  bool isMemorySSAEnabled() const;
 
   /// This class holds the mapping between values and value numbers.  It is used
   /// as an efficient mechanism to determine the expression-wise equivalence of
@@ -383,9 +391,8 @@ class GVNPass : public PassInfoMixin<GVNPass> {
   void assignBlockRPONumber(Function &F);
 };
 
-/// Create a legacy GVN pass. This also allows parameterizing whether or not
-/// MemDep is enabled.
-FunctionPass *createGVNPass(bool NoMemDepAnalysis = false);
+/// Create a legacy GVN pass.
+FunctionPass *createGVNPass();
 
 /// A simple and fast domtree-based GVN pass to hoist common expressions
 /// from sibling branches.

llvm/lib/Passes/PassBuilder.cpp

@@ -1042,6 +1042,8 @@ Expected<GVNOptions> parseGVNOptions(StringRef Params) {
       Result.setLoadPRESplitBackedge(Enable);
     } else if (ParamName == "memdep") {
       Result.setMemDep(Enable);
+    } else if (ParamName == "memoryssa") {
+      Result.setMemorySSA(Enable);
     } else {
       return make_error<StringError>(
           formatv("invalid GVN pass parameter '{0}' ", ParamName).str(),

llvm/lib/Passes/PassRegistry.def

@@ -526,7 +526,7 @@ FUNCTION_PASS_WITH_PARAMS(
     "gvn", "GVNPass", [](GVNOptions Opts) { return GVNPass(Opts); },
     parseGVNOptions,
     "no-pre;pre;no-load-pre;load-pre;no-split-backedge-load-pre;"
-    "split-backedge-load-pre;no-memdep;memdep")
+    "split-backedge-load-pre;no-memdep;memdep;no-memoryssa;memoryssa")
 FUNCTION_PASS_WITH_PARAMS(
     "hardware-loops", "HardwareLoopsPass",
     [](HardwareLoopOptions Opts) { return HardwareLoopsPass(Opts); },

llvm/lib/Transforms/Scalar/GVN.cpp

@@ -113,6 +113,8 @@ static cl::opt<bool>
 GVNEnableSplitBackedgeInLoadPRE("enable-split-backedge-in-load-pre",
                                 cl::init(false));
 static cl::opt<bool> GVNEnableMemDep("enable-gvn-memdep", cl::init(true));
+static cl::opt<bool> GVNEnableMemorySSA("enable-gvn-memoryssa",
+                                        cl::init(false));
 
 static cl::opt<uint32_t> MaxNumDeps(
     "gvn-max-num-deps", cl::Hidden, cl::init(100),
@@ -820,6 +822,10 @@ bool GVNPass::isMemDepEnabled() const {
   return Options.AllowMemDep.value_or(GVNEnableMemDep);
 }
 
+bool GVNPass::isMemorySSAEnabled() const {
+  return Options.AllowMemorySSA.value_or(GVNEnableMemorySSA);
+}
+
 PreservedAnalyses GVNPass::run(Function &F, FunctionAnalysisManager &AM) {
   // FIXME: The order of evaluation of these 'getResult' calls is very
   // significant! Re-ordering these variables will cause GVN when run alone to
@@ -833,6 +839,11 @@ PreservedAnalyses GVNPass::run(Function &F, FunctionAnalysisManager &AM) {
       isMemDepEnabled() ? &AM.getResult<MemoryDependenceAnalysis>(F) : nullptr;
   auto &LI = AM.getResult<LoopAnalysis>(F);
   auto *MSSA = AM.getCachedResult<MemorySSAAnalysis>(F);
+  if (isMemorySSAEnabled() && !MSSA) {
+    assert(!MemDep &&
+           "On-demand computation of MemSSA implies that MemDep is disabled!");
+    MSSA = &AM.getResult<MemorySSAAnalysis>(F);
+  }
   auto &ORE = AM.getResult<OptimizationRemarkEmitterAnalysis>(F);
   bool Changed = runImpl(F, AC, DT, TLI, AA, MemDep, LI, &ORE,
                          MSSA ? &MSSA->getMSSA() : nullptr);
@@ -861,7 +872,9 @@ void GVNPass::printPipeline(
     OS << (*Options.AllowLoadPRESplitBackedge ? "" : "no-")
        << "split-backedge-load-pre;";
   if (Options.AllowMemDep != std::nullopt)
-    OS << (*Options.AllowMemDep ? "" : "no-") << "memdep";
+    OS << (*Options.AllowMemDep ? "" : "no-") << "memdep;";
+  if (Options.AllowMemorySSA != std::nullopt)
+    OS << (*Options.AllowMemorySSA ? "" : "no-") << "memoryssa";
   OS << '>';
 }
 
@@ -3293,8 +3306,11 @@ class llvm::gvn::GVNLegacyPass : public FunctionPass {
 public:
   static char ID; // Pass identification, replacement for typeid
 
-  explicit GVNLegacyPass(bool NoMemDepAnalysis = !GVNEnableMemDep)
-      : FunctionPass(ID), Impl(GVNOptions().setMemDep(!NoMemDepAnalysis)) {
+  explicit GVNLegacyPass(bool MemDepAnalysis = GVNEnableMemDep,
+                         bool MemSSAAnalysis = GVNEnableMemorySSA)
+      : FunctionPass(ID), Impl(GVNOptions()
+                                   .setMemDep(MemDepAnalysis)
+                                   .setMemorySSA(MemSSAAnalysis)) {
     initializeGVNLegacyPassPass(*PassRegistry::getPassRegistry());
   }
 
@@ -3303,6 +3319,9 @@ class llvm::gvn::GVNLegacyPass : public FunctionPass {
       return false;
 
     auto *MSSAWP = getAnalysisIfAvailable<MemorySSAWrapperPass>();
+    if (Impl.isMemorySSAEnabled() && !MSSAWP)
+      MSSAWP = &getAnalysis<MemorySSAWrapperPass>();
+
     return Impl.runImpl(
         F, getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F),
         getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
@@ -3330,6 +3349,8 @@ class llvm::gvn::GVNLegacyPass : public FunctionPass {
     AU.addPreserved<LoopInfoWrapperPass>();
     AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
     AU.addPreserved<MemorySSAWrapperPass>();
+    if (Impl.isMemorySSAEnabled())
+      AU.addRequired<MemorySSAWrapperPass>();
   }
 
 private:
@@ -3341,6 +3362,7 @@ char GVNLegacyPass::ID = 0;
 INITIALIZE_PASS_BEGIN(GVNLegacyPass, "gvn", "Global Value Numbering", false, false)
 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 INITIALIZE_PASS_DEPENDENCY(MemoryDependenceWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
@@ -3349,6 +3371,4 @@ INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
 INITIALIZE_PASS_END(GVNLegacyPass, "gvn", "Global Value Numbering", false, false)
 
 // The public interface to this file...
-FunctionPass *llvm::createGVNPass(bool NoMemDepAnalysis) {
-  return new GVNLegacyPass(NoMemDepAnalysis);
-}
+FunctionPass *llvm::createGVNPass() { return new GVNLegacyPass(); }

llvm/test/Other/new-pm-print-pipeline.ll

@@ -31,8 +31,8 @@
 ; RUN: opt -disable-output -disable-verify -print-pipeline-passes -passes='function(loop-unroll<>,loop-unroll<partial;peeling;runtime;upperbound;profile-peeling;full-unroll-max=5;O1>,loop-unroll<no-partial;no-peeling;no-runtime;no-upperbound;no-profile-peeling;full-unroll-max=7;O1>)' < %s | FileCheck %s --match-full-lines --check-prefixes=CHECK-10
 ; CHECK-10: function(loop-unroll<O2>,loop-unroll<partial;peeling;runtime;upperbound;profile-peeling;full-unroll-max=5;O1>,loop-unroll<no-partial;no-peeling;no-runtime;no-upperbound;no-profile-peeling;full-unroll-max=7;O1>)
 
-; RUN: opt -disable-output -disable-verify -print-pipeline-passes -passes='function(gvn<>,gvn<pre;load-pre;split-backedge-load-pre;memdep>,gvn<no-pre;no-load-pre;no-split-backedge-load-pre;no-memdep>)' < %s | FileCheck %s --match-full-lines --check-prefixes=CHECK-11
-; CHECK-11: function(gvn<>,gvn<pre;load-pre;split-backedge-load-pre;memdep>,gvn<no-pre;no-load-pre;no-split-backedge-load-pre;no-memdep>)
+; RUN: opt -disable-output -disable-verify -print-pipeline-passes -passes='function(gvn<>,gvn<pre;load-pre;split-backedge-load-pre;memdep;memoryssa>,gvn<no-pre;no-load-pre;no-split-backedge-load-pre;no-memdep;no-memoryssa>)' < %s | FileCheck %s --match-full-lines --check-prefixes=CHECK-11
+; CHECK-11: function(gvn<>,gvn<pre;load-pre;split-backedge-load-pre;memdep;memoryssa>,gvn<no-pre;no-load-pre;no-split-backedge-load-pre;no-memdep;no-memoryssa>)
 
 ; RUN: opt -disable-output -disable-verify -print-pipeline-passes -passes='function(early-cse<>,early-cse<memssa>)' < %s | FileCheck %s --match-full-lines --check-prefixes=CHECK-12
 ; CHECK-12: function(early-cse<>,early-cse<memssa>)