LowerTypeTests: Fix quadratic complexity.

[pcc]

Currently we have quadratic complexity in LowerTypeTests because
ScopedSaveAliaseesAndUsed loops over all aliases for each disjoint
set, and the number of aliases and number of disjoint sets is
roughly proportional to the program size. Fix that by moving
ScopedSaveAliaseesAndUsed to LowerTypeTestsModule::lower() so that
we do this only once.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Peter Collingbourne (pcc)

Changes

Currently we have quadratic complexity in LowerTypeTests because
ScopedSaveAliaseesAndUsed loops over all aliases for each disjoint
set, and the number of aliases and number of disjoint sets is
roughly proportional to the program size. Fix that by moving
ScopedSaveAliaseesAndUsed to LowerTypeTestsModule::lower() so that
we do this only once.

---

Full diff: https://github.com/llvm/llvm-project/pull/135875.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/IPO/LowerTypeTests.cpp (+81-83)

diff --git a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
index 7cf7d74acfcfa..8e9f24dfc31fa 100644
--- a/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
+++ b/llvm/lib/Transforms/IPO/LowerTypeTests.cpp
@@ -1669,61 +1669,55 @@ void LowerTypeTestsModule::buildBitSetsFromFunctionsNative(
 
   lowerTypeTestCalls(TypeIds, JumpTable, GlobalLayout);
 
-  {
-    ScopedSaveAliaseesAndUsed S(M);
+  // Build aliases pointing to offsets into the jump table, and replace
+  // references to the original functions with references to the aliases.
+  for (unsigned I = 0; I != Functions.size(); ++I) {
+    Function *F = cast<Function>(Functions[I]->getGlobal());
+    bool IsJumpTableCanonical = Functions[I]->isJumpTableCanonical();
 
-    // Build aliases pointing to offsets into the jump table, and replace
-    // references to the original functions with references to the aliases.
-    for (unsigned I = 0; I != Functions.size(); ++I) {
-      Function *F = cast<Function>(Functions[I]->getGlobal());
-      bool IsJumpTableCanonical = Functions[I]->isJumpTableCanonical();
-
-      Constant *CombinedGlobalElemPtr = ConstantExpr::getInBoundsGetElementPtr(
-          JumpTableType, JumpTable,
-          ArrayRef<Constant *>{ConstantInt::get(IntPtrTy, 0),
-                               ConstantInt::get(IntPtrTy, I)});
-
-      const bool IsExported = Functions[I]->isExported();
-      if (!IsJumpTableCanonical) {
-        GlobalValue::LinkageTypes LT = IsExported
-                                           ? GlobalValue::ExternalLinkage
-                                           : GlobalValue::InternalLinkage;
-        GlobalAlias *JtAlias = GlobalAlias::create(F->getValueType(), 0, LT,
-                                                   F->getName() + ".cfi_jt",
-                                                   CombinedGlobalElemPtr, &M);
-        if (IsExported)
-          JtAlias->setVisibility(GlobalValue::HiddenVisibility);
-        else
-          appendToUsed(M, {JtAlias});
-      }
+    Constant *CombinedGlobalElemPtr = ConstantExpr::getInBoundsGetElementPtr(
+        JumpTableType, JumpTable,
+        ArrayRef<Constant *>{ConstantInt::get(IntPtrTy, 0),
+                             ConstantInt::get(IntPtrTy, I)});
+
+    const bool IsExported = Functions[I]->isExported();
+    if (!IsJumpTableCanonical) {
+      GlobalValue::LinkageTypes LT = IsExported ? GlobalValue::ExternalLinkage
+                                                : GlobalValue::InternalLinkage;
+      GlobalAlias *JtAlias = GlobalAlias::create(F->getValueType(), 0, LT,
+                                                 F->getName() + ".cfi_jt",
+                                                 CombinedGlobalElemPtr, &M);
+      if (IsExported)
+        JtAlias->setVisibility(GlobalValue::HiddenVisibility);
+      else
+        appendToUsed(M, {JtAlias});
+    }
 
-      if (IsExported) {
-        if (IsJumpTableCanonical)
-          ExportSummary->cfiFunctionDefs().emplace(F->getName());
-        else
-          ExportSummary->cfiFunctionDecls().emplace(F->getName());
-      }
+    if (IsExported) {
+      if (IsJumpTableCanonical)
+        ExportSummary->cfiFunctionDefs().emplace(F->getName());
+      else
+        ExportSummary->cfiFunctionDecls().emplace(F->getName());
+    }
 
-      if (!IsJumpTableCanonical) {
-        if (F->hasExternalWeakLinkage())
-          replaceWeakDeclarationWithJumpTablePtr(F, CombinedGlobalElemPtr,
-                                                 IsJumpTableCanonical);
-        else
-          replaceCfiUses(F, CombinedGlobalElemPtr, IsJumpTableCanonical);
-      } else {
-        assert(F->getType()->getAddressSpace() == 0);
-
-        GlobalAlias *FAlias =
-            GlobalAlias::create(F->getValueType(), 0, F->getLinkage(), "",
-                                CombinedGlobalElemPtr, &M);
-        FAlias->setVisibility(F->getVisibility());
-        FAlias->takeName(F);
-        if (FAlias->hasName())
-          F->setName(FAlias->getName() + ".cfi");
-        replaceCfiUses(F, FAlias, IsJumpTableCanonical);
-        if (!F->hasLocalLinkage())
-          F->setVisibility(GlobalVariable::HiddenVisibility);
-      }
+    if (!IsJumpTableCanonical) {
+      if (F->hasExternalWeakLinkage())
+        replaceWeakDeclarationWithJumpTablePtr(F, CombinedGlobalElemPtr,
+                                               IsJumpTableCanonical);
+      else
+        replaceCfiUses(F, CombinedGlobalElemPtr, IsJumpTableCanonical);
+    } else {
+      assert(F->getType()->getAddressSpace() == 0);
+
+      GlobalAlias *FAlias = GlobalAlias::create(
+          F->getValueType(), 0, F->getLinkage(), "", CombinedGlobalElemPtr, &M);
+      FAlias->setVisibility(F->getVisibility());
+      FAlias->takeName(F);
+      if (FAlias->hasName())
+        F->setName(FAlias->getName() + ".cfi");
+      replaceCfiUses(F, FAlias, IsJumpTableCanonical);
+      if (!F->hasLocalLinkage())
+        F->setVisibility(GlobalVariable::HiddenVisibility);
     }
   }
 
@@ -2339,39 +2333,43 @@ bool LowerTypeTestsModule::lower() {
   if (GlobalClasses.empty())
     return false;
 
-  // For each disjoint set we found...
-  for (const auto &C : GlobalClasses) {
-    if (!C->isLeader())
-      continue;
-
-    ++NumTypeIdDisjointSets;
-    // Build the list of type identifiers in this disjoint set.
-    std::vector<Metadata *> TypeIds;
-    std::vector<GlobalTypeMember *> Globals;
-    std::vector<ICallBranchFunnel *> ICallBranchFunnels;
-    for (auto M : GlobalClasses.members(*C)) {
-      if (isa<Metadata *>(M))
-        TypeIds.push_back(cast<Metadata *>(M));
-      else if (isa<GlobalTypeMember *>(M))
-        Globals.push_back(cast<GlobalTypeMember *>(M));
-      else
-        ICallBranchFunnels.push_back(cast<ICallBranchFunnel *>(M));
-    }
-
-    // Order type identifiers by unique ID for determinism. This ordering is
-    // stable as there is a one-to-one mapping between metadata and unique IDs.
-    llvm::sort(TypeIds, [&](Metadata *M1, Metadata *M2) {
-      return TypeIdInfo[M1].UniqueId < TypeIdInfo[M2].UniqueId;
-    });
+  {
+    ScopedSaveAliaseesAndUsed S(M);
+    // For each disjoint set we found...
+    for (const auto &C : GlobalClasses) {
+      if (!C->isLeader())
+        continue;
 
-    // Same for the branch funnels.
-    llvm::sort(ICallBranchFunnels,
-               [&](ICallBranchFunnel *F1, ICallBranchFunnel *F2) {
-                 return F1->UniqueId < F2->UniqueId;
-               });
+      ++NumTypeIdDisjointSets;
+      // Build the list of type identifiers in this disjoint set.
+      std::vector<Metadata *> TypeIds;
+      std::vector<GlobalTypeMember *> Globals;
+      std::vector<ICallBranchFunnel *> ICallBranchFunnels;
+      for (auto M : GlobalClasses.members(*C)) {
+        if (isa<Metadata *>(M))
+          TypeIds.push_back(cast<Metadata *>(M));
+        else if (isa<GlobalTypeMember *>(M))
+          Globals.push_back(cast<GlobalTypeMember *>(M));
+        else
+          ICallBranchFunnels.push_back(cast<ICallBranchFunnel *>(M));
+      }
 
-    // Build bitsets for this disjoint set.
-    buildBitSetsFromDisjointSet(TypeIds, Globals, ICallBranchFunnels);
+      // Order type identifiers by unique ID for determinism. This ordering is
+      // stable as there is a one-to-one mapping between metadata and unique
+      // IDs.
+      llvm::sort(TypeIds, [&](Metadata *M1, Metadata *M2) {
+        return TypeIdInfo[M1].UniqueId < TypeIdInfo[M2].UniqueId;
+      });
+
+      // Same for the branch funnels.
+      llvm::sort(ICallBranchFunnels,
+                 [&](ICallBranchFunnel *F1, ICallBranchFunnel *F2) {
+                   return F1->UniqueId < F2->UniqueId;
+                 });
+
+      // Build bitsets for this disjoint set.
+      buildBitSetsFromDisjointSet(TypeIds, Globals, ICallBranchFunnels);
+    }
   }
 
   allocateByteArrays();