[AArch64] Don't implicitly enable global isel on Darwin if code-model==large.

[lhames]

Summary

AArch64 GlobalISel doesn't support MachO's large code model, so this patch
adds a check for that combination before implicitly enabling it.

[paquette]

LGTM

llvm/trunk/lib/Target/AArch64/AArch64TargetMachine.cpp

if (getMCAsmInfo()->usesWindowsCFI()) {
     // exception-handling region (function, funclet, try block, etc.)
     // is a call.
     //
     // FIXME: We could elide the trap if the next instruction would be in
     // the same region anyway.
     this->Options.TrapUnreachable = true;
   }
 
-  // Enable GlobalISel at or below EnableGlobalISelAt0.
+  // Enable GlobalISel at or below EnableGlobalISelAt0, unless this is
+  // MachO/CodeModel::Large, which GlobalISel does not support.
   if (getOptLevel() <= EnableGlobalISelAtO &&
-      TT.getArch() != Triple::aarch64_32) {
+      TT.getArch() != Triple::aarch64_32 &&
+      !(getCodeModel() == CodeModel::Large && TT.isOSBinFormatMachO())) {
     setGlobalISel(true);
     setGlobalISelAbort(GlobalISelAbortMode::Disable);
   }
 
   // AArch64 supports the MachineOutliner.
   setMachineOutliner(true);
 
   // AArch64 supports default outlining behaviour.

llvm/trunk/test/CodeGen/AArch64/arm64-code-model-large-darwin.ll

+; Check that AArch64 is honoring code-model=large at -O0 and -O2.
+;
+; RUN: llc -mtriple=arm64-apple-darwin19 -code-model=large -O0 -o - %s | FileCheck %s
+; RUN: llc -mtriple=arm64-apple-darwin19 -code-model=large -O2 -o - %s | FileCheck %s
+
+; CHECK: adrp    [[REG1:x[0-9]+]], _bar@GOTPAGE
+; CHECK: ldr     [[REG1]], {{\[}}[[REG1]], _bar@GOTPAGEOFF]
+; CHECK: blr     [[REG1]]
+
+declare void @bar()
+
+define void @foo() {
+  call void @bar()
+  ret void
+}
+