[llvm] [DWARFVerifier] Allow overlapping ranges for ICF-merged functions (PR #117952)

[David Blaikie via llvm-commits]

================
@@ -622,7 +627,8 @@ unsigned DWARFVerifier::verifyDieRanges(const DWARFDie &Die,
   }
 
   // Verify that children don't intersect.
-  const auto IntersectingChild = ParentRI.insert(RI);
+  bool AllowDuplicates = Die.getTag() == DW_TAG_subprogram;
----------------
dwblaikie wrote:

Ah, yeah, looks like we don't even try to apply any verification constraints to ranges between CUs *shrug* they should probably have the same constraints, though - that exact overlap of any range is acceptable, but partial overlap is not. But ah well, I'm not pushing for improving that.

Let's look at lexical scope overlap, then... 

I think this example demonstrates almost all the overlapping cases (well, doesn't include distinct subprograms overlapping with each other, but otherwise I think it covers things):
```
int f1(bool a, bool b) {
  {
    int i = 3;
    {
      int j = 7;
      if (a)
        return 5;
    }
    {
      int j = 8;
      if (b)
        return 5;
    }
  }
  return 3;
}


int main() {
}
```
```
clang++-tot test.cpp -g -ffunction-sections -fbasic-block-sections=all -fuse-ld=gold -Wl,--icf=all
```
```
error: DIE has overlapping ranges in DW_AT_ranges attribute: [0x00000000000006a2, 0x00000000000006ae) and [0x00000000000006a2, 0x00000000000006ae)

0x0000000c:   DW_TAG_compile_unit [1] *
                DW_AT_producer [DW_FORM_strx1]  (indexed (00000000) string = "clang version 20.0.0git (git at github.com:llvm/llvm-project.git 8dd9f206b518a97132f3e2489ccc93704e638353)")
                DW_AT_language [DW_FORM_data2]  (DW_LANG_C_plus_plus_14)
                DW_AT_name [DW_FORM_strx1]      (indexed (00000001) string = "test.cpp")
                DW_AT_str_offsets_base [DW_FORM_sec_offset]     (0x00000008)
                DW_AT_stmt_list [DW_FORM_sec_offset]    (0x00000000)
                DW_AT_comp_dir [DW_FORM_strx1]  (indexed (00000002) string = "/usr/local/google/home/blaikie/dev/scratch")
                DW_AT_low_pc [DW_FORM_addr]     (0x0000000000000000)
                DW_AT_ranges [DW_FORM_rnglistx] (indexed (0x4) rangelist = 0x00000052
                   [0x0000000000000670, 0x00000000000006a2)
                   [0x00000000000006a2, 0x00000000000006ae)
                   [0x00000000000006ae, 0x00000000000006c4)
                   [0x00000000000006a2, 0x00000000000006ae)
                   [0x00000000000006c4, 0x00000000000006d0)
                   [0x00000000000006d0, 0x00000000000006d5)
                   [0x00000000000006e0, 0x00000000000006e8))
                DW_AT_addr_base [DW_FORM_sec_offset]    (0x00000008)
                DW_AT_rnglists_base [DW_FORM_sec_offset]        (0x0000000c)

error: DIE has overlapping ranges in DW_AT_ranges attribute: [0x00000000000006a2, 0x00000000000006ae) and [0x00000000000006a2, 0x00000000000006ae)

0x0000002b:   DW_TAG_subprogram [2] * (0x0000000c)
                DW_AT_ranges [DW_FORM_rnglistx] (indexed (0x0) rangelist = 0x00000020
                   [0x0000000000000670, 0x00000000000006a2)
                   [0x00000000000006a2, 0x00000000000006ae)
                   [0x00000000000006ae, 0x00000000000006c4)
                   [0x00000000000006a2, 0x00000000000006ae)
                   [0x00000000000006c4, 0x00000000000006d0)
                   [0x00000000000006d0, 0x00000000000006d5))
                DW_AT_frame_base [DW_FORM_exprloc]      (DW_OP_reg6)
                DW_AT_linkage_name [DW_FORM_strx1]      (indexed (00000003) string = "_Z2f1bb")
                DW_AT_name [DW_FORM_strx1]      (indexed (00000004) string = "f1")
                DW_AT_decl_file [DW_FORM_data1] ("/usr/local/google/home/blaikie/dev/scratch/test.cpp")
                DW_AT_decl_line [DW_FORM_data1] (1)
                DW_AT_type [DW_FORM_ref4]       (cu + 0x0087 => {0x00000087} "int")
                DW_AT_external [DW_FORM_flag_present]   (true)

error: DIE has overlapping ranges in DW_AT_ranges attribute: [0x00000000000006a2, 0x00000000000006ae) and [0x00000000000006a2, 0x00000000000006ae)

0x0000004d:   DW_TAG_lexical_block [4] * (0x0000002b)
                DW_AT_ranges [DW_FORM_rnglistx] (indexed (0x1) rangelist = 0x00000033
                   [0x0000000000000685, 0x00000000000006a2)
                   [0x00000000000006a2, 0x00000000000006ae)
                   [0x00000000000006ae, 0x00000000000006c4)
                   [0x00000000000006a2, 0x00000000000006ae))

error: DIEs have overlapping address ranges:
0x00000068: DW_TAG_lexical_block [4] * (0x0000004d)
              DW_AT_ranges [DW_FORM_rnglistx]   (indexed (0x3) rangelist = 0x0000004b
                 [0x00000000000006ae, 0x00000000000006c4)
                 [0x00000000000006a2, 0x00000000000006ae))

0x0000005a: DW_TAG_lexical_block [4] * (0x0000004d)
              DW_AT_ranges [DW_FORM_rnglistx]   (indexed (0x2) rangelist = 0x00000042
                 [0x000000000000068c, 0x00000000000006a2)
                 [0x00000000000006a2, 0x00000000000006ae))
```

https://github.com/llvm/llvm-project/pull/117952