[llvm] f4dd1bc - [AMDGPU] Fix leak and self-assignment in copy assignment operator (#107847)

[via llvm-commits]

Author: Fraser Cormack
Date: 2024-09-11T10:23:41+01:00
New Revision: f4dd1bc8fc625d3938f95b9d06aaaeebd2e90dca

URL: https://github.com/llvm/llvm-project/commit/f4dd1bc8fc625d3938f95b9d06aaaeebd2e90dca
DIFF: https://github.com/llvm/llvm-project/commit/f4dd1bc8fc625d3938f95b9d06aaaeebd2e90dca.diff

LOG: [AMDGPU] Fix leak and self-assignment in copy assignment operator (#107847)

A static analyzer identified that this operator was unsafe in the case
of self-assignment.

In the placement new statement, StringValue's copy constructor was being
implicitly called, which received a reference to "itself". In fact, it
was being passed an old StringValue at the same address - one whose
lifetime had already ended. The copy constructor was thus copying fields
from a dead object.

We need to be careful when switching active union members, and calling
the destructor on the old StringValue will avoid memory leaks which I
believe the old code exhibited.

Added: 
    

Modified: 
    llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h b/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
index 7af5e7388f841e..4cc60f50978996 100644
--- a/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
+++ b/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
@@ -100,19 +100,25 @@ struct SIArgument {
   SIArgument() : IsRegister(false), StackOffset(0) {}
   SIArgument(const SIArgument &Other) {
     IsRegister = Other.IsRegister;
-    if (IsRegister) {
-      ::new ((void *)std::addressof(RegisterName))
-          StringValue(Other.RegisterName);
-    } else
+    if (IsRegister)
+      new (&RegisterName) StringValue(Other.RegisterName);
+    else
       StackOffset = Other.StackOffset;
     Mask = Other.Mask;
   }
   SIArgument &operator=(const SIArgument &Other) {
+    // Default-construct or destruct the old RegisterName in case of switching
+    // union members
+    if (IsRegister != Other.IsRegister) {
+      if (Other.IsRegister)
+        new (&RegisterName) StringValue();
+      else
+        RegisterName.~StringValue();
+    }
     IsRegister = Other.IsRegister;
-    if (IsRegister) {
-      ::new ((void *)std::addressof(RegisterName))
-          StringValue(Other.RegisterName);
-    } else
+    if (IsRegister)
+      RegisterName = Other.RegisterName;
+    else
       StackOffset = Other.StackOffset;
     Mask = Other.Mask;
     return *this;