[PATCH] D111415: [Demangle] Add support for D simple qualified names

Wed Oct 13 08:22:13 PDT 2021

ljmf00 added inline comments.

================
Comment at: llvm/lib/Demangle/DLangDemangle.cpp:432-433
+                                  unsigned long Len) {
+  switch (Len) {
+  case 6:
+    if (strncmp(Mangled, "__ctor", Len) == 0) {
----------------
ljmf00 wrote:
> dblaikie wrote:
> > Might be easier to read with a StringSwitch (could make a StringRef from the Mnagled pointer and the length - maybe pass as StringRef here, rather than as the decomposed components) rather than a switch over length + strncmps?
> I guess you are missing the point of this switch. Maybe some comments can be added to cover this behaviour but the point here is: the length passed into parseLName is the length of the identifier name but not of the mangled name evaluated inside `strncmp`. This is specifically needed, because, for other special names, e.g. initializers (`__initZ`), a Z is suffixed indicating it is a special symbol. In order to verify that, extra length to accommodate the 'Z' char is needed.
> 
> The StringSwitch is not applicable here because of that, otherwise would be a good fit. I see optimizations that can be done, however, which is:
> 1. Use integer literals on `strncmp` instead of being calculated in runtime
> 2. Use a second inner switch to make the compiler optimize it with jump tables
Well, I realized that the first option is not doable here and the second one, from what I tested on clang 13, the optimizer can take what I suggested easily. https://godbolt.org/z/5dorfsWq9
If you have any other suggestions here that can increase readability, I would appreciate discussing them :)

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D111415/new/

https://reviews.llvm.org/D111415