ARM: do not relax Thumb1 -> Thumb2 if only Thumb1 is available.

After recognising that a certain narrow instruction might need a relocation to
be represented, we used to unconditionally relax it to a Thumb2 instruction to
permit this. Unfortunately, some CPUs (e.g. v6m) don't even have most Thumb2
instructions, so we end up emitting a completely invalid instruction.

Theoretically, ELF does have relocations for these situations; but they are
fairly unusable with such short ranges and the ABI document even says they're
documented "for completeness". So an error is probably better there too.

rdar://20391953

llvm-svn: 234195

1 files changed, 1 insertions, 6 deletions

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
index 3187d36f751..e1c17c689ed 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMachObjectWriter.cpp
@@ -88,6 +88,7 @@ static bool getARMFixupKindMachOInfo(unsigned Kind, unsigned &RelocType,
   case ARM::fixup_arm_ldst_pcrel_12:
   case ARM::fixup_arm_pcrel_10:
   case ARM::fixup_arm_adr_pcrel_12:
+  case ARM::fixup_arm_thumb_br:
     return false;
 
     // Handle 24-bit branch kinds.
@@ -101,12 +102,6 @@ static bool getARMFixupKindMachOInfo(unsigned Kind, unsigned &RelocType,
     Log2Size = llvm::Log2_32(4);
     return true;
 
-    // Handle Thumb branches.
-  case ARM::fixup_arm_thumb_br:
-    RelocType = unsigned(MachO::ARM_THUMB_RELOC_BR22);
-    Log2Size = llvm::Log2_32(2);
-    return true;
-
   case ARM::fixup_t2_uncondbranch:
   case ARM::fixup_arm_thumb_bl:
   case ARM::fixup_arm_thumb_blx: