Reland "Lower `@llvm.global_dtors` using `__cxa_atexit` on MachO"

For MachO, lower `@llvm.global_dtors` into `@llvm_global_ctors` with
`__cxa_atexit` calls to avoid emitting the deprecated `__mod_term_func`.

Reuse the existing `WebAssemblyLowerGlobalDtors.cpp` to accomplish this.

Enable fallback to the old behavior via Clang driver flag
(`-fregister-global-dtors-with-atexit`) or llc / code generation flag
(`-lower-global-dtors-via-cxa-atexit`).  This escape hatch will be
removed in the future.

Differential Revision: https://reviews.llvm.org/D121736

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/CommandFlags.cpp b/llvm/lib/CodeGen/CommandFlags.cpp
index 761e79e..cdf160d 100644
--- a/llvm/lib/CodeGen/CommandFlags.cpp
+++ b/llvm/lib/CodeGen/CommandFlags.cpp
@@ -79,6 +79,7 @@ CGOPT(bool, StackSymbolOrdering)
 CGOPT(bool, StackRealign)
 CGOPT(std::string, TrapFuncName)
 CGOPT(bool, UseCtors)
+CGOPT(bool, LowerGlobalDtorsViaCxaAtExit)
 CGOPT(bool, RelaxELFRelocations)
 CGOPT_EXP(bool, DataSections)
 CGOPT_EXP(bool, FunctionSections)
@@ -346,6 +347,12 @@ codegen::RegisterCodeGenFlags::RegisterCodeGenFlags() {
                                 cl::init(false));
   CGBINDOPT(UseCtors);
 
+  static cl::opt<bool> LowerGlobalDtorsViaCxaAtExit(
+      "lower-global-dtors-via-cxa-atexit",
+      cl::desc("Lower llvm.global_dtors (global destructors) via __cxa_atexit"),
+      cl::init(true));
+  CGBINDOPT(LowerGlobalDtorsViaCxaAtExit);
+
   static cl::opt<bool> RelaxELFRelocations(
       "relax-elf-relocations",
       cl::desc(
@@ -529,6 +536,7 @@ codegen::InitTargetOptionsFromCodeGenFlags(const Triple &TheTriple) {
   Options.GuaranteedTailCallOpt = getEnableGuaranteedTailCallOpt();
   Options.StackSymbolOrdering = getStackSymbolOrdering();
   Options.UseInitArray = !getUseCtors();
+  Options.LowerGlobalDtorsViaCxaAtExit = getLowerGlobalDtorsViaCxaAtExit();
   Options.RelaxELFRelocations = getRelaxELFRelocations();
   Options.DataSections =
       getExplicitDataSections().getValueOr(TheTriple.hasDefaultDataSections());