[PATCH] D55919: [DebugInfo] Omit location list entries with empty ranges

[David Stenberg via Phabricator via llvm-commits]

dstenb created this revision.
dstenb added reviewers: davide, aprantl, dblaikie.
dstenb added a project: debug-info.
Herald added subscribers: llvm-commits, JDevlieghere, javed.absar.

This fixes PR39710. In that case we emitted a location list looking like
this:

.Ldebug_loc0:

  .quad   .Lfunc_begin0-.Lfunc_begin0
  .quad   .Lfunc_begin0-.Lfunc_begin0
  .short  1                       # Loc expr size
  .byte   85                      # DW_OP_reg5
  .quad   .Lfunc_begin0-.Lfunc_begin0
  .quad   .Lfunc_end0-.Lfunc_begin0
  .short  1                       # Loc expr size
  .byte   85                      # super-register DW_OP_reg5
  .quad   0
  .quad   0

As seen, the first entry's beginning and ending addresses evalute to 0,
which meant that the entry inadvertently became a "end of list" entry,
resulting in the location list ending sooner than expected.

To fix this, omit all entries with empty ranges. Location list entries
with empty ranges do not have any effect, as specified by DWARF, so we
might as well drop them:

"A location list entry (but not a base address selection or end of list
 entry) whose beginning and ending addresses are equal has no effect
 because the size of the range covered by such an entry is zero."


Repository:
  rL LLVM

https://reviews.llvm.org/D55919

Files:
  lib/CodeGen/AsmPrinter/DwarfDebug.cpp
  test/DebugInfo/ARM/PR26163.ll
  test/DebugInfo/X86/PR26148.ll
  test/DebugInfo/X86/pieces-3.ll

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