[clang] 0768b05 - Avoid redundant work when computing vtable vcall visibility

[Teresa Johnson via cfe-commits]

Author: Teresa Johnson
Date: 2020-11-24T12:06:24-08:00
New Revision: 0768b0576a938b6a4832884384fcb02cd2f74e09

URL: https://github.com/llvm/llvm-project/commit/0768b0576a938b6a4832884384fcb02cd2f74e09
DIFF: https://github.com/llvm/llvm-project/commit/0768b0576a938b6a4832884384fcb02cd2f74e09.diff

LOG: Avoid redundant work when computing vtable vcall visibility

Add a Visited set to avoid repeatedly processing the same base classes
in complex class hierarchies. This cut down the compile time of one
source file from >12min to ~1min.

Differential Revision: https://reviews.llvm.org/D91676

Added: 
    

Modified: 
    clang/lib/CodeGen/CGVTables.cpp
    clang/lib/CodeGen/CodeGenModule.h
    clang/lib/CodeGen/MicrosoftCXXABI.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index 65b3b0c5f53d..75afc860cc47 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -1294,8 +1294,16 @@ bool CodeGenModule::HasHiddenLTOVisibility(const CXXRecordDecl *RD) {
   return !HasLTOVisibilityPublicStd(RD);
 }
 
-llvm::GlobalObject::VCallVisibility
-CodeGenModule::GetVCallVisibilityLevel(const CXXRecordDecl *RD) {
+llvm::GlobalObject::VCallVisibility CodeGenModule::GetVCallVisibilityLevel(
+    const CXXRecordDecl *RD, llvm::DenseSet<const CXXRecordDecl *> &Visited) {
+  // If we have already visited this RD (which means this is a recursive call
+  // since the initial call should have an empty Visited set), return the max
+  // visibility. The recursive calls below compute the min between the result
+  // of the recursive call and the current TypeVis, so returning the max here
+  // ensures that it will have no effect on the current TypeVis.
+  if (!Visited.insert(RD).second)
+    return llvm::GlobalObject::VCallVisibilityTranslationUnit;
+
   LinkageInfo LV = RD->getLinkageAndVisibility();
   llvm::GlobalObject::VCallVisibility TypeVis;
   if (!isExternallyVisible(LV.getLinkage()))
@@ -1307,13 +1315,15 @@ CodeGenModule::GetVCallVisibilityLevel(const CXXRecordDecl *RD) {
 
   for (auto B : RD->bases())
     if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
-      TypeVis = std::min(TypeVis,
-                    GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl()));
+      TypeVis = std::min(
+          TypeVis,
+          GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
 
   for (auto B : RD->vbases())
     if (B.getType()->getAsCXXRecordDecl()->isDynamicClass())
-      TypeVis = std::min(TypeVis,
-                    GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl()));
+      TypeVis = std::min(
+          TypeVis,
+          GetVCallVisibilityLevel(B.getType()->getAsCXXRecordDecl(), Visited));
 
   return TypeVis;
 }
@@ -1382,7 +1392,9 @@ void CodeGenModule::EmitVTableTypeMetadata(const CXXRecordDecl *RD,
 
   if (getCodeGenOpts().VirtualFunctionElimination ||
       getCodeGenOpts().WholeProgramVTables) {
-    llvm::GlobalObject::VCallVisibility TypeVis = GetVCallVisibilityLevel(RD);
+    llvm::DenseSet<const CXXRecordDecl *> Visited;
+    llvm::GlobalObject::VCallVisibility TypeVis =
+        GetVCallVisibilityLevel(RD, Visited);
     if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
       VTable->setVCallVisibilityMetadata(TypeVis);
   }

diff  --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 7d812b6658dc..c59570598b0d 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1333,8 +1333,11 @@ class CodeGenModule : public CodeGenTypeCache {
   /// a virtual function call could be made which ends up being dispatched to a
   /// member function of this class. This scope can be wider than the visibility
   /// of the class itself when the class has a more-visible dynamic base class.
+  /// The client should pass in an empty Visited set, which is used to prevent
+  /// redundant recursive processing.
   llvm::GlobalObject::VCallVisibility
-  GetVCallVisibilityLevel(const CXXRecordDecl *RD);
+  GetVCallVisibilityLevel(const CXXRecordDecl *RD,
+                          llvm::DenseSet<const CXXRecordDecl *> &Visited);
 
   /// Emit type metadata for the given vtable using the given layout.
   void EmitVTableTypeMetadata(const CXXRecordDecl *RD,

diff  --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 8046b7afce57..c16c72dc93d5 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -1649,8 +1649,9 @@ void MicrosoftCXXABI::emitVTableTypeMetadata(const VPtrInfo &Info,
   // TODO: Should VirtualFunctionElimination also be supported here?
   // See similar handling in CodeGenModule::EmitVTableTypeMetadata.
   if (CGM.getCodeGenOpts().WholeProgramVTables) {
+    llvm::DenseSet<const CXXRecordDecl *> Visited;
     llvm::GlobalObject::VCallVisibility TypeVis =
-        CGM.GetVCallVisibilityLevel(RD);
+        CGM.GetVCallVisibilityLevel(RD, Visited);
     if (TypeVis != llvm::GlobalObject::VCallVisibilityPublic)
       VTable->setVCallVisibilityMetadata(TypeVis);
   }