LTO: Decide upfront whether to use opaque/non-opaque pointer types

LTO code may end up mixing bitcode files from various sources varying in
their use of opaque pointer types. The current strategy to decide
between opaque / typed pointers upon the first bitcode file loaded does
not work here, since we could be loading a non-opaque bitcode file first
and would then be unable to load any files with opaque pointer types
later.

So for LTO this:
- Adds an `lto::Config::OpaquePointer` option and enforces an upfront
  decision between the two modes.
- Adds `-opaque-pointers`/`-no-opaque-pointers` options to the gold
  plugin; disabled by default.
- `--opaque-pointers`/`--no-opaque-pointers` options with
  `-plugin-opt=-opaque-pointers`/`-plugin-opt=-no-opaque-pointers`
  aliases to lld; disabled by default.
- Adds an `-lto-opaque-pointers` option to the `llvm-lto2` tool.
- Changes the clang driver to pass `-plugin-opt=-opaque-pointers` to
  the linker in LTO modes when clang was configured with opaque
  pointers enabled by default.

This fixes https://github.com/llvm/llvm-project/issues/55377

Differential Revision: https://reviews.llvm.org/D125847

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/tools/gold/gold-plugin.cpp b/llvm/tools/gold/gold-plugin.cpp
index 019bfe0..a9814c6 100644
--- a/llvm/tools/gold/gold-plugin.cpp
+++ b/llvm/tools/gold/gold-plugin.cpp
@@ -208,6 +208,8 @@ namespace options {
   static std::string stats_file;
   // Asserts that LTO link has whole program visibility
   static bool whole_program_visibility = false;
+  // Use opaque pointer types.
+  static bool opaque_pointers = true;
 
   // Optimization remarks filename, accepted passes and hotness options
   static std::string RemarksFilename;
@@ -308,6 +310,10 @@ namespace options {
       RemarksFormat = std::string(opt);
     } else if (opt.consume_front("stats-file=")) {
       stats_file = std::string(opt);
+    } else if (opt == "opaque-pointers") {
+      opaque_pointers = true;
+    } else if (opt == "no-opaque-pointers") {
+      opaque_pointers = false;
     } else {
       // Save this option to pass to the code generator.
       // ParseCommandLineOptions() expects argv[0] to be program name. Lazily
@@ -957,6 +963,8 @@ static std::unique_ptr<LTO> createLTO(IndexWriteCallback OnIndexWrite,
 
   Conf.HasWholeProgramVisibility = options::whole_program_visibility;
 
+  Conf.OpaquePointers = options.opaque_pointers;
+
   Conf.StatsFile = options::stats_file;
   return std::make_unique<LTO>(std::move(Conf), Backend,
                                 options::ParallelCodeGenParallelismLevel);