[clang] [lld] [llvm] [llvm][lld][clang] Delay initializing TargetOptions in LTO builds until a Triple is available (PR #179509)

[Paul Kirth via cfe-commits]

================
@@ -46,47 +46,52 @@ static std::string getThinLTOOutputFile(Ctx &ctx, StringRef modulePath) {
 static lto::Config createConfig(Ctx &ctx) {
   lto::Config c;
 
-  // LLD supports the new relocations and address-significance tables.
-  c.Options = initTargetOptionsFromCodeGenFlags();
-  c.Options.EmitAddrsig = true;
-  for (StringRef C : ctx.arg.mllvmOpts)
-    c.MllvmArgs.emplace_back(C.str());
-
-  // Always emit a section per function/datum with LTO.
-  c.Options.FunctionSections = true;
-  c.Options.DataSections = true;
-
-  // Check if basic block sections must be used.
-  // Allowed values for --lto-basic-block-sections are "all",
-  // "<file name specifying basic block ids>", or none.  This is the equivalent
-  // of -fbasic-block-sections= flag in clang.
-  if (!ctx.arg.ltoBasicBlockSections.empty()) {
-    if (ctx.arg.ltoBasicBlockSections == "all") {
-      c.Options.BBSections = BasicBlockSection::All;
-    } else if (ctx.arg.ltoBasicBlockSections == "labels") {
-      c.Options.BBAddrMap = true;
-      Warn(ctx)
-          << "'--lto-basic-block-sections=labels' is deprecated; Please use "
-             "'--lto-basic-block-address-map' instead";
-    } else if (ctx.arg.ltoBasicBlockSections == "none") {
-      c.Options.BBSections = BasicBlockSection::None;
-    } else {
-      ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
-          MemoryBuffer::getFile(ctx.arg.ltoBasicBlockSections.str());
-      if (!MBOrErr) {
-        ErrAlways(ctx) << "cannot open " << ctx.arg.ltoBasicBlockSections << ":"
-                       << MBOrErr.getError().message();
+  // Set up the callback to modify TargetOptions.
+  c.ModifyTargetOptions = [&](TargetOptions &Options) -> void {
+    // LLD supports the new relocations and address-significance tables.
+    Options.EmitAddrsig = true;
+    // Always emit a section per function/datum with LTO.
+    Options.FunctionSections = true;
+    Options.DataSections = true;
+
+    // Check if basic block sections must be used.
+    // Allowed values for --lto-basic-block-sections are "all",
+    // "<file name specifying basic block ids>", or none.  This is the
+    // equivalent of -fbasic-block-sections= flag in clang.
+    if (!ctx.arg.ltoBasicBlockSections.empty()) {
+      if (ctx.arg.ltoBasicBlockSections == "all") {
+        Options.BBSections = BasicBlockSection::All;
+      } else if (ctx.arg.ltoBasicBlockSections == "labels") {
+        Options.BBAddrMap = true;
+        Warn(ctx)
+            << "'--lto-basic-block-sections=labels' is deprecated; Please use "
+               "'--lto-basic-block-address-map' instead";
+      } else if (ctx.arg.ltoBasicBlockSections == "none") {
+        Options.BBSections = BasicBlockSection::None;
       } else {
-        c.Options.BBSectionsFuncListBuf = std::move(*MBOrErr);
+        ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
+            MemoryBuffer::getFile(ctx.arg.ltoBasicBlockSections.str());
----------------
ilovepi wrote:

I'm pretty sure we always only call the callback once. I also tried just duping the conditional block w/ all the options above the lambda. That almost works, but something in the move capture is breaking and I don't understand what the issue is, since i just did` [MB = std::move(*MBOrErr), ...]`, which (AFAIK) is the only way to move `std::unique_ptr<T>` into a closure.

```console
/usr/local/google/home/paulkirth/llvm-fork/lld/ELF/LTO.cpp:94:41: error: no viable overloaded '='
   94 |           options.BBSectionsFuncListBuf = std::move(MB);
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~
/usr/local/google/home/paulkirth/fuchsia/prebuilt/third_party/clang/linux-x64/bin/../include/c++/v1/__memory/shared_ptr.h:504:42: note: candidate function not viable: no known conversion from '__libcpp_remove_reference_t<const std::unique_ptr<llvm::MemoryBuffer, std::default_delete<llvm::MemoryBuffer>> &>' (aka 'const std::unique_ptr<llvm::MemoryBuffer>') to 'const shared_ptr<llvm::MemoryBuffer>' for 1st argument
  504 |   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr& __r) _NOEXCEPT {
      |                                          ^         ~~~~~~~~~~~~~~~~~~~~~
/usr/local/google/home/paulkirth/fuchsia/prebuilt/third_party/clang/linux-x64/bin/../include/c++/v1/__memory/shared_ptr.h:515:42: note: candidate function not viable: no known conversion from '__libcpp_remove_reference_t<const std::unique_ptr<llvm::MemoryBuffer, std::default_delete<llvm::MemoryBuffer>> &>' (aka 'const std::unique_ptr<llvm::MemoryBuffer>') to 'shared_ptr<llvm::MemoryBuffer>' for 1st argument
  515 |   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr&& __r) _NOEXCEPT {
      |                                          ^         ~~~~~~~~~~~~~~~~
/usr/local/google/home/paulkirth/fuchsia/prebuilt/third_party/clang/linux-x64/bin/../include/c++/v1/__memory/shared_ptr.h:510:42: note: candidate template ignored: could not match 'shared_ptr' against 'std::unique_ptr'
  510 |   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr<_Yp>& __r) _NOEXCEPT {
      |                                          ^
/usr/local/google/home/paulkirth/fuchsia/prebuilt/third_party/clang/linux-x64/bin/../include/c++/v1/__memory/shared_ptr.h:521:42: note: candidate template ignored: could not match 'shared_ptr' against 'std::unique_ptr'
  521 |   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr<_Yp>&& __r) {
      |                                          ^
/usr/local/google/home/paulkirth/fuchsia/prebuilt/third_party/clang/linux-x64/bin/../include/c++/v1/__memory/shared_ptr.h:541:42: note: candidate template ignored: deduced type 'unique_ptr<llvm::MemoryBuffer, std::default_delete<llvm::MemoryBuffer>>' of 1st parameter does not match adjusted type '__libcpp_remove_reference_t<const std::unique_ptr<llvm::MemoryBuffer, std::default_delete<llvm::MemoryBuffer>> &>' (aka 'const std::unique_ptr<llvm::MemoryBuffer>') of argument [with _Yp = llvm::MemoryBuffer, _Dp = std::default_delete<llvm::MemoryBuffer>, $2 = 0]
  541 |   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(unique_ptr<_Yp, _Dp>&& __r) {
      |                                          ^
```

Maybe something odd with `__libcpp_remove_ref`?

https://github.com/llvm/llvm-project/pull/179509