[llvm-bugs] [Bug 36323] New: Issues with C99 VLA implementation

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Feb 9 11:22:17 PST 2018


https://bugs.llvm.org/show_bug.cgi?id=36323

            Bug ID: 36323
           Summary: Issues with C99 VLA implementation
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: paul_robinson at playstation.sony.com
                CC: llvm-bugs at lists.llvm.org

I've spun this off from bug 36322 to track additional issues with
the current implementation of DWARF descriptions of C99 VLAs.

Initially I was curious what happened if a function with a VLA was
inlined into another function.  Adrian Prantl pointed out the test
  llvm/test/DebugInfo/X86/vla-dependencies.ll
which I started playing with.

Even without optimization, some curious things happen.
The subrange_type has a DW_AT_type which points to something called 
"sizetype" which does not exist in the source.  It also doesn't share 
an abbrev with the other base types, because its attributes are in a 
different order; this suggests some poor internal coding practice at least, 
although it's not actually invalid DWARF.

With optimization, LLVM asserts, which is worth its own bug.

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