[Object] Update ObjectFile::makeTriple for XCOFF

[hubert.reinterpretcast]

Summary

When we encounter an XCOFF file, reflect that in the triple information. In addition to knowing the object file format, we know that the associated OS is AIX.

This means that we can expect that there is no output difference in the processing of an XCOFF32 input file between cases where the triple is left unspecified by the user and cases where the user specifies --triple powerpc-ibm-aix explicitly.

[jhenderson]

Did you see that there are a bunch of test failures according to the pre-merge build? Don't know if they're related, but I guess that they are somehow.

[hubert.reinterpretcast]

In D77025#1949281, @jhenderson wrote:

Did you see that there are a bunch of test failures according to the pre-merge build? Don't know if they're related, but I guess that they are somehow.

Yes, I did. I am not sure that the pre-merge testing has proven to be reliably noise free. The functional behaviour change is limited to cases where the library returns "true" for isXCOFF; there is no reason to expect that to be the case for the environment that the failure logs report.

[jasonliu]

LGTM.

[MaskRay]

D76907 will change bdnzfl 9, $+8696 to print the target address instead. objdump -d output is not guaranteed to be able to re-assemble.

If you want to restore the $+offset behavior, you can customize IP->setPrintBranchImmAsAddress(true); in tools/llvm-objdump/llvm-objdump.cpp

(I'd prefer not, because powerpc*-linux-gnu-objdump -d prints the target address as well.)

llvm/lib/Object/ObjectFile.cpp

Triple ObjectFile::makeTriple() const {
 
   // For ARM targets, try to use the build attributes to build determine
   // the build target. Target features are also added, but later during
   // disassembly.
   if (Arch == Triple::arm || Arch == Triple::armeb)
     setARMSubArch(TheTriple);
 
   // TheTriple defaults to ELF, and COFF doesn't have an environment:
-  // the best we can do here is indicate that it is mach-o.
-  if (isMachO())
+  // something we can do here is indicate that it is mach-o.
+  if (isMachO()) {
     TheTriple.setObjectFormat(Triple::MachO);
-
-  if (isCOFF()) {
+  } else if (isCOFF()) {
     const auto COFFObj = cast<COFFObjectFile>(this);
     if (COFFObj->getArch() == Triple::thumb)
       TheTriple.setTriple("thumbv7-windows");
+  } else if (isXCOFF()) {
+    // XCOFF implies AIX.
+    TheTriple.setOS(Triple::AIX);
+    TheTriple.setObjectFormat(Triple::XCOFF);
   }
 
   return TheTriple;
 }
 
 Expected<std::unique_ptr<ObjectFile>>
 ObjectFile::createObjectFile(MemoryBufferRef Object, file_magic Type) {
   StringRef Data = Object.getBuffer();

llvm/test/CodeGen/PowerPC/aix-return55.ll

 ;CHECKOBJ-NEXT:       8: 68 65 6c 6c                   xori 5, 3, 27756
 ;CHECKOBJ-NEXT:       c: 6f 77 6f 72 xoris 23, 27, 28530
 ;CHECKOBJ-NEXT:      10: 0a 00 00 00 tdlti 0, 0{{[[:space:]] *}}
 ;CHECKOBJ-NEXT: Disassembly of section .data:{{[[:space:]] *}}
 ;CHECKOBJ-NEXT: 00000018 <a>:
 ;CHECKOBJ-NEXT:      18: 00 01 23 45                   <unknown>
 ;CHECKOBJ-NEXT:      1c: 67 8a bc de                   oris 10, 28, 48350{{[[:space:]] *}}
 ;CHECKOBJ-NEXT: 00000020 <d>:
-;CHECKOBJ-NEXT:      20: 40 14 00 00                   bdnzf   20, .+0
+;CHECKOBJ-NEXT:      20: 40 14 00 00                   bdnzf   20, $+0
 ;CHECKOBJ-NEXT:      24: 00 00 00 00                   <unknown>{{[[:space:]] *}}
 ;CHECKOBJ-NEXT: 00000028 <foo>:
 ;CHECKOBJ-NEXT:      28: 00 00 00 00                   <unknown>
 ;CHECKOBJ-NEXT:      2c: 00 00 00 34                   <unknown>
 ;CHECKOBJ-NEXT:      30: 00 00 00 00                   <unknown>
 
 ;CHECKSECT: Sections [
 ;CHECKSECT-NEXT:   Section {

llvm/test/tools/llvm-objdump/XCOFF/disassemble-all.test

 CHECK-NEXT:       9c: 00 00 00 00                   <unknown>
 CHECK:        000000a0 <b>:
 CHECK-NEXT:       a0: 00 00 30 39                   <unknown>
 CHECK:        Disassembly of section .bss:
 CHECK:        000000a4 <a>:
 CHECK-NEXT:        ...
 CHECK:        Disassembly of section .tdata:
 CHECK:        00000000 <d>:
-CHECK-NEXT:        0: 40 09 21 f9                   bdnzfl  9, .+8696
+CHECK-NEXT:        0: 40 09 21 f9                   bdnzfl  9, $+8696
 CHECK-NEXT:        4: f0 1b 86 6e                   <unknown>
 CHECK:        Disassembly of section .tbss:
 CHECK:        00000008 <c>:
 CHECK-NEXT:        ...