[PATCH] D75375: [MCDwarf] Generate DWARF v5 .debug_rnglists for assembly files

[Fangrui Song via Phabricator via llvm-commits]

MaskRay marked 2 inline comments as done.
MaskRay added inline comments.


================
Comment at: llvm/lib/MC/MCDwarf.cpp:48-59
+void mcdwarf::emitListsTableHeaderStart(MCStreamer *S, MCSymbol *TableStart,
+                                        MCSymbol *TableEnd) {
+  S->AddComment("Length");
+  S->emitAbsoluteSymbolDiff(TableEnd, TableStart, 4);
+  S->emitLabel(TableStart);
+  S->AddComment("Version");
+  S->emitInt16(S->getContext().getDwarfVersion());
----------------
dblaikie wrote:
> Please pass "S" by reference here, since it's unconditionally dereferenced (so the null state isn't needed) - this will simplify some of the callers too (x.get() -> *x)
> 
> TableStart and TableEnd can remain pointers since their underlying APIs use them/they're more "tokens" to pass around.
Agreed with the analysis.

It also makes sense for `MCStreamer::emitAbsoluteSymbolDiff` to take references as parameters. However, `MCSymbol *` typed parameters are much more common than `MCSymbol &`.


================
Comment at: llvm/lib/MC/MCDwarf.cpp:1120-1124
+    MCSymbol *StartSymbol =
+        context.createTempSymbol("debug_rnglists_start", true, true);
+    MCSymbol *EndSymbol =
+        context.createTempSymbol("debug_rnglists_end", true, true);
+    mcdwarf::emitListsTableHeaderStart(MCOS, StartSymbol, EndSymbol);
----------------
dblaikie wrote:
> Might be worth considering rolling the start/end label creation into this utility function & having this function return the EndSymbol for later use?
> 
> (some of the other "emit a header with the usual length field" implementations in AsmPrinter use this idiom - the function creates both labels, returns the end label for the outer code to emit at the end of the contents)
```
// https://github.com/llvm/llvm-project/blob/master/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp#L2425
static MCSymbol *emitLoclistsTableHeader(AsmPrinter *Asm,
                                         const DwarfDebug &DD) {
  MCSymbol *TableStart = Asm->createTempSymbol("debug_loclist_table_start");
  MCSymbol *TableEnd = Asm->createTempSymbol("debug_loclist_table_end");
  mcdwarf::emitListsTableHeaderStart(*Asm->OutStreamer, TableStart, TableEnd);
```

The temporary labels may have a different name (loclist). Shall I add another parameter `SymbolName` accepting either `debug_loclists_header` or `debug_rnglists_header`?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D75375/new/

https://reviews.llvm.org/D75375