Remove bit-rotten CppBackend.

[jyknight]

Summary

This backend was supposed to generate C++ code which will re-construct
the LLVM IR passed as input. This seems to me to have very marginal
usefulness in the first place.

However, the code has never been updated to use IRBuilder, which makes
its current value negative -- people who look at the output may be
steered to use the *wrong* C++ APIs to construct IR.

Furthermore, it's generated code that doesn't compile since at least
2013.

[• rafael]

LGTM

llvm/trunk/CMakeLists.txt

 set(LLVM_EXAMPLES_BINARY_DIR ${LLVM_BINARY_DIR}/examples)
 set(LLVM_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/include)
 
 set(LLVM_ALL_TARGETS
   AArch64
   AMDGPU
   ARM
   BPF
-  CppBackend
   Hexagon
   Mips
   MSP430
   NVPTX
   PowerPC
   Sparc
   SystemZ
   X86

llvm/trunk/docs/CodeGenerator.rst

 specific to the code generator for a particular target.  First we start with a
 table that summarizes what features are supported by each target.
 
 .. _target-feature-matrix:
 
 Target Feature Matrix
 ---------------------
 
-Note that this table does not include the C backend or Cpp backends, since they
-do not use the target independent code generator infrastructure.  It also
-doesn't list features that are not supported fully by any target yet.  It
-considers a feature to be supported if at least one subtarget supports it.  A
-feature being supported means that it is useful and works for most cases, it
-does not indicate that there are zero known bugs in the implementation.  Here is
-the key:
+Note that this table does not list features that are not supported fully by any
+target yet.  It considers a feature to be supported if at least one subtarget
+supports it.  A feature being supported means that it is useful and works for
+most cases, it does not indicate that there are zero known bugs in the
+implementation.  Here is the key:
 
 :raw-html:`<table border="1" cellspacing="0">`
 :raw-html:`<tr>`
 :raw-html:`<th>Unknown</th>`
 :raw-html:`<th>Not Applicable</th>`
 :raw-html:`<th>No support</th>`
 :raw-html:`<th>Partial Support</th>`
 :raw-html:`<th>Complete Support</th>`

llvm/trunk/docs/GettingStarted.rst

 |                         | running the install action of the build files.     |
 +-------------------------+----------------------------------------------------+
 | LLVM_TARGETS_TO_BUILD   | A semicolon delimited list controlling which       |
 |                         | targets will be built and linked into llc. This is |
 |                         | equivalent to the ``--enable-targets`` option in   |
 |                         | the configure script. The default list is defined  |
 |                         | as ``LLVM_ALL_TARGETS``, and can be set to include |
 |                         | out-of-tree targets. The default value includes:   |
-|                         | ``AArch64, AMDGPU, ARM, BPF, CppBackend, Hexagon,  |
-|                         | Mips, MSP430, NVPTX, PowerPC, Sparc, SystemZ       |
-|                         | X86, XCore``.                                      |
+|                         | ``AArch64, AMDGPU, ARM, BPF, Hexagon, Mips,        |
+|                         | MSP430, NVPTX, PowerPC, Sparc, SystemZ, X86,       |
+|                         | XCore``.                                           |
 +-------------------------+----------------------------------------------------+
 | LLVM_ENABLE_DOXYGEN     | Build doxygen-based documentation from the source  |
 |                         | code This is disabled by default because it is     |
 |                         | slow and generates a lot of output.                |
 +-------------------------+----------------------------------------------------+
 | LLVM_ENABLE_SPHINX      | Build sphinx-based documentation from the source   |
 |                         | code. This is disabled by default because it is    |
 |                         | slow and generates a lot of output.                |

llvm/trunk/lib/Target/LLVMBuild.txt

 ; will typically require only insertion of a line.
 [common]
 subdirectories =
  AMDGPU
  ARM
  AArch64
  AVR
  BPF
- CppBackend
  Lanai
  Hexagon
  MSP430
  NVPTX
  Mips
  PowerPC
  Sparc
  SystemZ

llvm/trunk/utils/GenLibDeps.pl

foreach my $lib (@libs ) {
     $libpath =~ s/(.+)AsmPrinter$/Target\/$1\/AsmPrinter/;
     $libpath =~ s/(.+)AsmParser$/Target\/$1\/AsmParser/;
     $libpath =~ s/(.+)Info$/Target\/$1\/TargetInfo/;
     $libpath =~ s/(.+)Disassembler$/Target\/$1\/Disassembler/;
     $libpath =~ s/SelectionDAG/CodeGen\/SelectionDAG/;
     $libpath =~ s/^AsmPrinter/CodeGen\/AsmPrinter/;
     $libpath =~ s/^BitReader/Bitcode\/Reader/;
     $libpath =~ s/^BitWriter/Bitcode\/Writer/;
-    $libpath =~ s/^CppBackend/Target\/CppBackend/;
     $libpath =~ s/^MSIL/Target\/MSIL/;
     $libpath =~ s/^Core/IR/;
     $libpath =~ s/^Instrumentation/Transforms\/Instrumentation/;
     $libpath =~ s/^Interpreter/ExecutionEngine\/Interpreter/;
     $libpath =~ s/^JIT/ExecutionEngine\/JIT/;
     $libpath =~ s/^ScalarOpts/Transforms\/Scalar/;
     $libpath =~ s/^TransformUtils/Transforms\/Utils/;
     $libpath =~ s/^ipa/Analysis\/IPA/;
foreach my $lib (@libs ) {
     $libpath =~ s/(.+)AsmPrinter$/Target\/$1\/AsmPrinter/;
     $libpath =~ s/(.+)AsmParser$/Target\/$1\/AsmParser/;
     $libpath =~ s/(.+)Info$/Target\/$1\/TargetInfo/;
     $libpath =~ s/(.+)Disassembler$/Target\/$1\/Disassembler/;
     $libpath =~ s/SelectionDAG/CodeGen\/SelectionDAG/;
     $libpath =~ s/^AsmPrinter/CodeGen\/AsmPrinter/;
     $libpath =~ s/^BitReader/Bitcode\/Reader/;
     $libpath =~ s/^BitWriter/Bitcode\/Writer/;
-    $libpath =~ s/^CppBackend/Target\/CppBackend/;
     $libpath =~ s/^MSIL/Target\/MSIL/;
     $libpath =~ s/^Core/VMCore/;
     $libpath =~ s/^Instrumentation/Transforms\/Instrumentation/;
     $libpath =~ s/^Interpreter/ExecutionEngine\/Interpreter/;
     $libpath =~ s/^JIT/ExecutionEngine\/JIT/;
     $libpath =~ s/^ScalarOpts/Transforms\/Scalar/;
     $libpath =~ s/^TransformUtils/Transforms\/Utils/;
     $libpath =~ s/^ipa/Analysis\/IPA/;