[PATCH] D70524: Support DebugInfo generation for auto return type for C++ functions.

[David Blaikie via Phabricator via cfe-commits]

dblaikie added a comment.

In D70524#1761514 <https://reviews.llvm.org/D70524#1761514>, @awpandey wrote:

> Hi @aprantl  and @dblaikie. Currently, there is no test case for the unspecified type, so I have added that in the regression test suite.


It looks to me like there are a few tests for unspecified_type already:

$ grep -r unspecified_type llvm/test
llvm/test/Assembler/debug-info.ll:; CHECK-NEXT: !7 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "decltype(nullptr)")
llvm/test/Assembler/debug-info.ll:!8 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "decltype(nullptr)")
llvm/test/DebugInfo/COFF/types-std-nullptr-t.ll:!6 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "decltype(nullptr)")
llvm/test/DebugInfo/X86/template.ll:; VERIFY-NOT: error: DIE has DW_AT_type with incompatible tag DW_TAG_unspecified_type
llvm/test/DebugInfo/X86/template.ll:; CHECK: [[NULLPTR]]:{{ *}}DW_TAG_unspecified_type
llvm/test/DebugInfo/X86/template.ll:!34 = !DIBasicType(tag: DW_TAG_unspecified_type, name: "decltype(nullptr)")

@aprantl @probinson - I'm going to voice a little more objection to this feature as I think I did when it was being discussed for DWARF standardization - feel free to push back/veto me/etc: Describing this seems of limited value to consumers - the function cannot be called if the return type hasn't been resolved. I think modeling these sort of situations the same way member function templates are would be fine - omit the declaration entirely in translation units that have no function definition for an auto-returning function.

The only difference between this and templates is that we /can/ describe it & it can be useful for overload resolution - but the same is true of all functions (non-member, member, etc) & no DWARF producer I know of produces all function declarations into their output, so I'm not sure "make overload resolution work" is really a worthwhile goal. (without template descripttions (not the instantiations, but the templates themselves which we currently have no way of describing even if we wanted to) I don't think it's actually achievable)



================
Comment at: clang/test/CodeGenCXX/debug-info-auto-return.cpp:12-15
+class myClass {
+  int low, high;
+
+public:
----------------
I'd probably make this a struct, rather than a class with a public member - access modifiers aren't relevant to this test, so far as I can tell, so might as well just have everything public by using a struct.


================
Comment at: clang/test/CodeGenCXX/debug-info-auto-return.cpp:13
+class myClass {
+  int low, high;
+
----------------
No need for any member variables, I think?


================
Comment at: clang/test/CodeGenCXX/debug-info-auto-return.cpp:20-23
+  if (low > high)
+    return 1;
+  else
+    return 1;
----------------
Could strip out the body here - leave a single "return 0;" in there if that's useful/needed.


================
Comment at: llvm/test/DebugInfo/X86/debug-info-auto-return.ll:5-25
+;class myClass {
+;    int low, high;
+;
+;  public:
+;      myClass(int a, int b) {
+;            low = a;
+;                high = b;
----------------
This code seems more complicated than it needs to be (it doesn't need any logic in the body of the functions, for instance, I think? Nor any member variables, nor 'main', etc) & the indentation should be fixed/made consistent.


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  https://reviews.llvm.org/D70524/new/

https://reviews.llvm.org/D70524