Temporarily revert "Change -gz and -Wa,--compress-debug-sections to use gABI compression (SHF_COMPRESSED)"

This affects users of older (pre 2.26) binutils in such a way that they can't necessarily
work around it as it doesn't support the compress option on the command line. Reverting
to unblock them and we can revisit whether to make this change now or fix how we want
to express the option.

This reverts commit bdb2133/r360403.

llvm-svn: 360703

Author: echristo

clang/docs/ReleaseNotes.rst

@@ -77,10 +77,7 @@ Modified Compiler Flags
 
 - `clang -dumpversion` now returns the version of Clang itself.
 
-- On ELF, ``-gz`` now defaults to ``-gz=zlib``. It produces ``SHF_COMPRESSED``
-  style compression of debug information. GNU binutils 2.26 or newer, or lld is
-  required to link produced object files. Use ``-gz=zlib-gnu`` to get the old
-  behavior.
+- ...
 
 New Pragmas in Clang
 --------------------

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1052,7 +1052,8 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   if (const Arg *A = Args.getLastArg(OPT_compress_debug_sections,
                                      OPT_compress_debug_sections_EQ)) {
     if (A->getOption().getID() == OPT_compress_debug_sections) {
-      Opts.setCompressDebugSections(llvm::DebugCompressionType::Z);
+      // TODO: be more clever about the compression type auto-detection
+      Opts.setCompressDebugSections(llvm::DebugCompressionType::GNU);
     } else {
       auto DCT = llvm::StringSwitch<llvm::DebugCompressionType>(A->getValue())
                      .Case("none", llvm::DebugCompressionType::None)

clang/tools/driver/cc1as_main.cpp

@@ -221,7 +221,8 @@ bool AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
   if (const Arg *A = Args.getLastArg(OPT_compress_debug_sections,
                                      OPT_compress_debug_sections_EQ)) {
     if (A->getOption().getID() == OPT_compress_debug_sections) {
-      Opts.CompressDebugSections = llvm::DebugCompressionType::Z;
+      // TODO: be more clever about the compression type auto-detection
+      Opts.CompressDebugSections = llvm::DebugCompressionType::GNU;
     } else {
       Opts.CompressDebugSections =
           llvm::StringSwitch<llvm::DebugCompressionType>(A->getValue())