@llvm/pr-subscribers-llvm-adt

Author: Kazu Hirata (kazutakahirata)

diff --git a/llvm/include/llvm/ADT/SmallSet.h b/llvm/include/llvm/ADT/SmallSet.h
index eb434bcb71717..96a68fb8da0e2 100644
--- a/llvm/include/llvm/ADT/SmallSet.h
+++ b/llvm/include/llvm/ADT/SmallSet.h
@@ -268,8 +268,17 @@ class SmallSet {
 
 /// If this set is of pointer values, transparently switch over to using
 /// SmallPtrSet for performance.
+///
+/// We use this middleman class DeprecatedSmallSet so that the deprecation
+/// warning works.  Placing LLVM_DEPRECATED just before SmallSet below won't
+/// work.
+template <typename PointeeType, unsigned N>
+class LLVM_DEPRECATED("Use SmallPtrSet instead", "SmallPtrSet")
+    DeprecatedSmallSet : public SmallPtrSet<PointeeType *, N> {};
+
 template <typename PointeeType, unsigned N>
-class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
+class SmallSet<PointeeType *, N> : public DeprecatedSmallSet<PointeeType *, N> {
+};
 
 /// Equality comparison for SmallSet.
 ///

This code is turning SmallSet<T *> into SmallPtrSet<T **> (extra pointer level), which results in build errors if it gets used. The issue is DeprecatedSmallSet is a template, not a specialization, so its PointeeType is the pointer not the pointee.

This code is turning SmallSet<T *> into SmallPtrSet<T **> (extra pointer level), which results in build errors if it gets used. The issue is DeprecatedSmallSet is a template, not a specialization, so its PointeeType is the pointer not the pointee.

Can you fix forward? This should be simple from the sounds of it.

For posterity: #155117

Note, this is also still in the docs: https://llvm.org/docs/ProgrammersManual.html#llvm-adt-smallset-h

after this PR, i am seeing ~1800+ messages of the form
llvm/include/llvm/ADT/SmallSet.h:280:43: warning: ‘template<class PointerType, unsigned int N> class llvm::DeprecatedSmallSet’ is deprecated: Use SmallPtrSet instead [-Wdeprecated-declarations]

was this expected ?

after this PR, i am seeing ~1800+ messages of the form llvm/include/llvm/ADT/SmallSet.h:280:43: warning: ‘template<class PointerType, unsigned int N> class llvm::DeprecatedSmallSet’ is deprecated: Use SmallPtrSet instead [-Wdeprecated-declarations]

was this expected ?

In llvm and its subprojects, or in a downstream project?

llvm.org main branch, lots of projects . i am building with these enabled
-DLLVM_ENABLE_PROJECTS="clang;lld;clang-tools-extra;flang"
-DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;openmp;offload;compiler-rt;libunwind"

Any downstream files trying to use headers that has #include <SmallSet.h> will get warnings, there is no use of SmallSet at all.

llvm-project/build# cat t.cpp
#include "llvm/CodeGen/MachineDominators.h"
llvm-project/build# /usr/bin/c++ t.cpp -I llvm-project/llvm/include -Illvm-project/build/include -c

In file included from llvm-project/llvm/include/llvm/CodeGen/MachineDominators.h:17,
                 from t.cpp:1:
llvm-project/llvm/include/llvm/ADT/SmallSet.h:280:43: warning: ‘template<class PointerType, unsigned int N> class llvm::DeprecatedSmallSet’ is deprecated: Use SmallPtrSet instead [-Wdeprecated-declarations]
  280 | class SmallSet<PointeeType *, N> : public DeprecatedSmallSet<PointeeType *, N> {
      |                                           ^~~~~~~~~~~~~~~~~~
llvm-project/llvm/include/llvm/ADT/SmallSet.h:277:5: note: declared here
  277 |     DeprecatedSmallSet : public SmallPtrSet<PointerType, N> {};
      |     ^~~~~~~~~~~~~~~~~~

I'm seeing gcc warn unconditionally (godbolt link) but clang only warn if the template is used. Maybe this should be reverted?

Reverting in #155622