Emit DW_AT_main_subprogram

This changes rustc to emit DW_AT_main_subprogram on the "main" program.
This lets gdb suitably stop at the user's main in response to
"start" (rather than the library's main, which is what happens
currently).

Fixes #32620
r? michaelwoerister

1 files changed, 6 insertions, 0 deletions

diff --git a/src/rustllvm/RustWrapper.cpp b/src/rustllvm/RustWrapper.cpp
index 34ee7d552f3..798febcbcd6 100644
--- a/src/rustllvm/RustWrapper.cpp
+++ b/src/rustllvm/RustWrapper.cpp
@@ -346,6 +346,7 @@ enum class LLVMRustDIFlags : uint32_t {
   FlagStaticMember = (1 << 12),
   FlagLValueReference = (1 << 13),
   FlagRValueReference = (1 << 14),
+  FlagMainSubprogram      = (1 << 21),
   // Do not add values that are not supported by the minimum LLVM
   // version we support!
 };
@@ -432,6 +433,11 @@ static unsigned fromRust(LLVMRustDIFlags Flags) {
   if (isSet(Flags & LLVMRustDIFlags::FlagRValueReference)) {
     Result |= DINode::DIFlags::FlagRValueReference;
   }
+#if LLVM_RUSTLLVM || LLVM_VERSION_GE(4, 0)
+  if (isSet(Flags & LLVMRustDIFlags::FlagMainSubprogram)) {
+    Result |= DINode::DIFlags::FlagMainSubprogram;
+  }
+#endif
 
   return Result;
 }