Inlining and zero-cost abstractions tend to produce volumes of debug
info with identical ranges. When built with full debugging information
(the equivalent of -g2) librustc_driver.so has 2.1 million entries in
.debug_ranges. But only 1.1 million of those entries are unique. While
in principle all duplicates could be eliminated with a hashtable,
checking to see if the new range is exactly identical to the previous
range and skipping a new addition if it is is sufficient to eliminate
99.99% of the duplicates. This reduces the size of librustc_driver.so's
.debug_ranges section by 35%, or the overall binary size a little more
than 1%.

This reverts commit 9bbd2bf654634cd95dd0be7948ec8402c3c76e1e.

Accidental commit: https://github.com/llvm/llvm-project/pull/68131#issuecomment-1749430207

Added support for Type Units in monolithic DWARF in .debug_names.

This patch fixes:

  llvm/lib/CodeGen/AsmPrinter/DwarfFile.cpp:109:10: error: unused
  variable 'Ret' [-Werror,-Wunused-variable]

Differential Revision: https://reviews.llvm.org/D158676

I'm planning to deprecate and eventually remove llvm::empty.

I thought about replacing llvm::empty(x) with std::empty(x), but it
turns out that all uses can be converted to x.empty().  That is, no
use requires the ability of std::empty to accept C arrays and
std::initializer_list.

Differential Revision: https://reviews.llvm.org/D133677

Add SwitchSection to return switchSection. The API will be removed soon.

Discourse thread: https://discourse.llvm.org/t/include-what-you-use-include-cleanup
Differential Revision: https://reviews.llvm.org/D121332

SizeOf() method of DIE values(unsigned SizeOf(const AsmPrinter *AP, dwarf::Form Form) const)
depends on AsmPrinter. AsmPrinter is too specific class here. This patch removes dependency
on AsmPrinter and use dwarf::FormParams structure instead. It allows calculate DIE values
size without using AsmPrinter. That refactoring is useful for D96035([dsymutil][DWARFlinker]
implement separate multi-thread processing for compile units.)

Differential Revision: https://reviews.llvm.org/D116997

Use forward declarations where possible, move includes down to DwarfFile.cpp and avoid duplicate includes.