[Target][XCOFF] Correctly halt when mixing AIX or XCOFF with ppc64le

The code to prevent using `PPCXCOFFMCAsmInfo` with little-endian targets
used an incorrect check. Also, there does not appear to be sufficient
earlier checking to prevent failing this check, so the check here is
upgraded to be a `report_fatal_error`.

`PPCAIXAsmPrinter` was also missing a check against use with
little-endian targets. This patch adds such a check in.

Author: hubert-reinterpretcast

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCAsmInfo.cpp

@@ -56,6 +56,7 @@ PPCELFMCAsmInfo::PPCELFMCAsmInfo(bool is64Bit, const Triple& T) {
 void PPCXCOFFMCAsmInfo::anchor() {}
 
 PPCXCOFFMCAsmInfo::PPCXCOFFMCAsmInfo(bool Is64Bit, const Triple &T) {
-  assert(!IsLittleEndian && "Little-endian XCOFF not supported.");
+  if (T.getArch() == Triple::ppc64le)
+    report_fatal_error("XCOFF is not supported for little-endian targets");
   CodePointerSize = CalleeSaveStackSlotSize = Is64Bit ? 8 : 4;
 }

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -151,7 +151,11 @@ class PPCAIXAsmPrinter : public PPCAsmPrinter {
 
 public:
   PPCAIXAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
-      : PPCAsmPrinter(TM, std::move(Streamer)) {}
+      : PPCAsmPrinter(TM, std::move(Streamer)) {
+    if (MAI->isLittleEndian())
+      report_fatal_error(
+          "cannot create AIX PPC Assembly Printer for a little-endian target");
+  }
 
   StringRef getPassName() const override { return "AIX PPC Assembly Printer"; }
 

llvm/test/CodeGen/PowerPC/aix-xcoff-endian-error.ll

@@ -0,0 +1,13 @@
+; Check that use of the AIX/XCOFF related classes with ppc64le would
+; cause llc to die with an appropriate message instead of proceeding
+; with an invalid state.
+
+; RUN: not --crash llc < %s -mtriple powerpc64le--aix-xcoff 2>&1 \
+; RUN:   | FileCheck --check-prefix=AIXXCOFF %s
+; AIXXCOFF: ERROR: XCOFF is not supported for little-endian
+
+; RUN: not --crash llc < %s -mtriple powerpc64le--aix-macho 2>&1 \
+; RUN:   | FileCheck --check-prefix=AIXMACHO %s
+; AIXMACHO: ERROR: cannot create AIX PPC Assembly Printer for a little-endian target
+
+define i32 @a() { ret i32 0 }