[PATCH] D143487: [IR] Allow destruction of symbol table entries regardless of DiscardValueNames

[Yevgeny Rouban via Phabricator via llvm-commits]

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//Value::setNameImpl()// is used both to set and reset name of the value.
In destructor of //Function// all arguments get reset their names (see //Function::clearArguments()//).
If the arguments had their names set (e.g. when the function was created with LLVMContex::DiscardValueNames == true) then their ValueName entries referred by the function's symbol table must be destructed. They are not destructed if LLVMContex::DiscardValueNames is set to false because of the fast path in //Value::setNameImpl()//. See the new test cases that demonstrate the problem. Without the fix they both crash in the function's destructor.

In //Value::setNameImpl()// this patch removes the fast path return for DiscardValueNames == true to allow destruction of ValueName entries.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D143487

Files:
  llvm/lib/IR/Value.cpp
  llvm/unittests/IR/BasicBlockTest.cpp


Index: llvm/unittests/IR/BasicBlockTest.cpp
===================================================================
--- llvm/unittests/IR/BasicBlockTest.cpp
+++ llvm/unittests/IR/BasicBlockTest.cpp
@@ -541,5 +541,44 @@
   BB0->erase(BB0->begin(), BB0->end());
   EXPECT_TRUE(BB0->empty());
 }
+
+TEST(BasicBlockTest, DiscardValueNames) {
+  const char *ModuleString = "declare void @f(i32 %dangling)";
+  SMDiagnostic Err;
+  LLVMContext Ctx;
+  { // Scope of M.
+    auto M = parseAssemblyString(ModuleString, Err, Ctx);
+    EXPECT_TRUE(M.get());
+    EXPECT_FALSE(Ctx.shouldDiscardValueNames());
+  }
+  { // Scope of M.
+    auto M = parseAssemblyString(ModuleString, Err, Ctx);
+    EXPECT_TRUE(M.get());
+    Ctx.setDiscardValueNames(true);
+  }
+}
+
+TEST(BasicBlockTest, DiscardValueNames2) {
+  SMDiagnostic Err;
+  LLVMContext Ctx;
+  Module M("Mod", Ctx);
+  auto FTy = FunctionType::get(Type::getVoidTy(M.getContext()),
+                               {Type::getInt32Ty(Ctx)}, /*isVarArg=*/false);
+  { // Scope of F.
+    Function *F = Function::Create(FTy, Function::ExternalLinkage, "f", &M);
+    F->getArg(0)->setName("dangling");
+    F->removeFromParent();
+    EXPECT_FALSE(Ctx.shouldDiscardValueNames());
+    delete F;
+  }
+  { // Scope of F.
+    Function *F = Function::Create(FTy, Function::ExternalLinkage, "f", &M);
+    F->getArg(0)->setName("dangling");
+    F->removeFromParent();
+    Ctx.setDiscardValueNames(true);
+    delete F;
+  }
+}
+
 } // End anonymous namespace.
 } // End llvm namespace.
Index: llvm/lib/IR/Value.cpp
===================================================================
--- llvm/lib/IR/Value.cpp
+++ llvm/lib/IR/Value.cpp
@@ -315,10 +315,6 @@
 }
 
 void Value::setNameImpl(const Twine &NewName) {
-  // Fast-path: LLVMContext can be set to strip out non-GlobalValue names
-  if (getContext().shouldDiscardValueNames() && !isa<GlobalValue>(this))
-    return;
-
   // Fast path for common IRBuilder case of setName("") when there is no name.
   if (NewName.isTriviallyEmpty() && !hasName())
     return;
@@ -339,6 +335,9 @@
   if (getSymTab(this, ST))
     return;  // Cannot set a name on this value (e.g. constant).
 
+  bool NeedNewName =
+      !getContext().shouldDiscardValueNames() || isa<GlobalValue>(this);
+
   if (!ST) { // No symbol table to update?  Just do the change.
     if (NameRef.empty()) {
       // Free the name for this value.
@@ -351,9 +350,11 @@
     destroyValueName();
 
     // Create the new name.
-    MallocAllocator Allocator;
-    setValueName(ValueName::create(NameRef, Allocator));
-    getValueName()->setValue(this);
+    if (NeedNewName) {
+      MallocAllocator Allocator;
+      setValueName(ValueName::create(NameRef, Allocator));
+      getValueName()->setValue(this);
+    }
     return;
   }
 
@@ -369,7 +370,8 @@
   }
 
   // Name is changing to something new.
-  setValueName(ST->createValueName(NameRef, this));
+  if (NeedNewName)
+    setValueName(ST->createValueName(NameRef, this));
 }
 
 void Value::setName(const Twine &NewName) {


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