[llvm-mc] The object form of the GNU triple should be the same as the string form.

[dsanders]

Summary

GetTarget() may modify TripleName without also updating TheTriple.
This can lead to situations where the MCObjectStreamer has a different triple
to the rest of LLVM.

This inconsistency caused sparc-little-endian.s to pass on Windows because most
of LLVM had sparcel-pc-win32 while MCObjectStreamer had "". I believe the same
kind of thing was also true of Darwin.

[rengolin]

Ouch! This is a really bad design, thanks for the fix and the comment.

For the future, I believe we should either do the normalization in GetTarget and make sure no other function does, or don't change the triple at all in there. Hidden side effects of that magnitude are really horrible... :(

But not for this patch. LGTM. Thanks!

test/MC/Sparc/sparc-little-endian.s

-! RUN: llvm-mc %s -arch=sparcel -show-encoding | FileCheck %s
-! RUN: llvm-mc -arch=sparcel -filetype=obj < %s | llvm-objdump -d - | FileCheck %s --check-prefix=CHECK-OBJ
+! RUN: llvm-mc %s -triple=sparcel-linux-gnu -show-encoding | FileCheck %s
+! RUN: llvm-mc -triple=sparcel-linux-gnu -filetype=obj < %s | llvm-objdump -d - | FileCheck %s --check-prefix=CHECK-OBJ
 
         ! CHECK-OBJ: .text:
         .BB0:
 
         ! Ensure instructions are emitted in reversed byte order:
 
         ! CHECK: call %g1     ! encoding: [0x00,0x40,0xc0,0x9f]
         ! CHECK-OBJ: 0: 00 40 c0 9f  call %g1
         call %g1
 
         ! ...and that fixups are applied to the correct bytes.
 
         ! CHECK: ba .BB0      ! encoding: [A,A,0b10AAAAAA,0x10]
         ! CHECK-NEXT:         ! fixup A - offset: 0, value: .BB0, kind: fixup_sparc_br22
         ! CHECK-OBJ: 4: ff ff bf 10  ba 4194303
         ba .BB0

tools/llvm-mc/llvm-mc.cpp

int main(int argc, char **argv) {
   llvm::InitializeAllDisassemblers();
 
   // Register the target printer for --version.
   cl::AddExtraVersionPrinter(TargetRegistry::printRegisteredTargetsForVersion);
 
   cl::ParseCommandLineOptions(argc, argv, "llvm machine code playground\n");
   MCTargetOptions MCOptions = InitMCTargetOptionsFromFlags();
   TripleName = Triple::normalize(TripleName);
-  Triple TheTriple(TripleName);
   setDwarfDebugFlags(argc, argv);
 
   setDwarfDebugProducer();
 
   const char *ProgName = argv[0];
   const Target *TheTarget = GetTarget(ProgName);
   if (!TheTarget)
     return 1;
+  // Now that GetTarget() has (potentially) replaced TripleName, it's safe to
+  // construct the Triple object.
+  Triple TheTriple(TripleName);
 
   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferPtr =
       MemoryBuffer::getFileOrSTDIN(InputFilename);
   if (std::error_code EC = BufferPtr.getError()) {
     errs() << ProgName << ": " << EC.message() << '\n';
     return 1;
   }
   MemoryBuffer *Buffer = BufferPtr->get();