Michael137 wrote:
> Hi @Michael137, we are seeing a failure in one of our internal tests that I
> bisected back to this change. Consider the following code:
>
> ```c++
> struct X
> {
> static const int constant = 1;
> int x;
>
> X() { x = constant; }
> };
> const int X::constant;
>
> int main()
> {
> X x;
> x.x = X::constant;
> x.x = X::constant;
> x.x = X::constant;
> x.x = X::constant;
> x.x = X::constant;
> return 0;
> }
> ```
>
> Prior to your change, the compiler would generate the following DWARF for the
> constant value:
>
> ```
> 0x0000003a: DW_TAG_member
> DW_AT_name ("constant")
> DW_AT_type (0x00000057 "const int")
> DW_AT_decl_file ("/home/dyung/sandbox/test.cpp")
> DW_AT_decl_line (3)
> DW_AT_external (true)
> DW_AT_declaration (true)
> DW_AT_const_value (1)
> ```
>
> After your change, the DW_AT_const_value is gone from this DW_TAG_member
> group, but doesn't appear anywhere else in the DWARF output which seems to
> indicate that it was dropped completely which does not seem to be correct. Is
> this intended or am I missing something?
> Hi @Michael137, we are seeing a failure in one of our internal tests that I
> bisected back to this change. Consider the following code:
>
> ```c++
> struct X
> {
> static const int constant = 1;
> int x;
>
> X() { x = constant; }
> };
> const int X::constant;
>
> int main()
> {
> X x;
> x.x = X::constant;
> x.x = X::constant;
> x.x = X::constant;
> x.x = X::constant;
> x.x = X::constant;
> return 0;
> }
> ```
>
> Prior to your change, the compiler would generate the following DWARF for the
> constant value:
>
> ```
> 0x0000003a: DW_TAG_member
> DW_AT_name ("constant")
> DW_AT_type (0x00000057 "const int")
> DW_AT_decl_file ("/home/dyung/sandbox/test.cpp")
> DW_AT_decl_line (3)
> DW_AT_external (true)
> DW_AT_declaration (true)
> DW_AT_const_value (1)
> ```
>
> After your change, the DW_AT_const_value is gone from this DW_TAG_member
> group, but doesn't appear anywhere else in the DWARF output which seems to
> indicate that it was dropped completely which does not seem to be correct. Is
> this intended or am I missing something?
Right, we stopped putting the `DW_AT_const_value` on the declaration. Instead
we put either the location or the constant on the definition, depending on
what's available. In your example you define the variable out-of-class which
would generate a `DW_TAG_variable` with a location, so we don't emit the
constant for it on the definition. What's the nature of the failure? Would you
instead be able to read the value out of the definition?
CC @dwblaikie
https://github.com/llvm/llvm-project/pull/71780
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