[llvm-bugs] [Bug 26619] New: Global const static float debug info

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26619

            Bug ID: 26619
           Summary: Global const static float debug info
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: ewan at codeplay.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

In the example below there isn't enough DWARF present to get the value of g_pi:

const static double g_pi = 3.14;
const static int g_ret_code = 0;
#define M_PI 3.14

int main()
{
    const double local = M_PI / g_pi;
    return g_ret_code;
}





This produces the following relevant IR with -O0 & -g3, where we can see that
the values for both g_pi and g_ret_code are present in the debug meta-data. So
far so good.

!9 = !DIGlobalVariable(name: "g_pi", scope: !0, file: !1, line: 1, type: !10,
isLocal: true, isDefinition: true, variable: double 3.140000e+00)
!10 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !11)
!11 = !DIBasicType(name: "double", size: 64, align: 64, encoding: DW_ATE_float)
!12 = !DIGlobalVariable(name: "g_ret_code", scope: !0, file: !1, line: 2, type:
!13, isLocal: true, isDefinition: true, variable: i32 0)
!13 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !7)





However looking at the DWARF we can see that although the variable g_ret_code
has its value hardcoded into the
DWARF via DW_AT_const_value, g_pi has no DW_AT_const_value entry. There also
isn't a DW_AT_location attribute for g_pi, so the debugger has no
way to locate the value.

DWARF snippet:
< 1><0x0000002a>    DW_TAG_variable
                      DW_AT_name                  "g_pi"
                      DW_AT_type                  <0x00000035>
                      DW_AT_decl_file             0x00000001
/home/ewan/Desktop/Scratch/c/clang_test/main.c
                      DW_AT_decl_line             0x00000001
< 1><0x00000035>    DW_TAG_const_type
                      DW_AT_type                  <0x0000003a>
< 1><0x0000003a>    DW_TAG_base_type
                      DW_AT_name                  "double"
                      DW_AT_encoding              DW_ATE_float
                      DW_AT_byte_size             0x00000008
< 1><0x00000041>    DW_TAG_variable
                      DW_AT_name                  "g_ret_code"
                      DW_AT_type                  <0x0000004d>
                      DW_AT_decl_file             0x00000001
/home/ewan/Desktop/Scratch/c/clang_test/main.c
                      DW_AT_decl_line             0x00000002
                      DW_AT_const_value           0x00000000
< 1><0x0000004d>    DW_TAG_const_type
                      DW_AT_type                  <0x00000052>



Although the problem variable in this example was a double I've also seen this
with float, so something to do with non-intergral types

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