ARM Disassembler: sign extend branch immediates.

Not sure about BLXi, but this is what the old disassembler did.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@137156 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
index 6087a61..307ce88 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -1214,11 +1214,11 @@
   if (pred == 0xF) {
     Inst.setOpcode(ARM::BLXi);
     imm |= fieldFromInstruction32(Insn, 24, 1) << 1;
-    Inst.addOperand(MCOperand::CreateImm(imm));
+    Inst.addOperand(MCOperand::CreateImm(SignExtend32<26>(imm)));
     return true;
   }
 
-  Inst.addOperand(MCOperand::CreateImm(imm));
+  Inst.addOperand(MCOperand::CreateImm(SignExtend32<26>(imm)));
   if (!DecodePredicateOperand(Inst, pred, Address, Decoder)) return false;
 
   return true;