[AVR] Fixed bug in AVRBranchSelector

It wasn't taking into account that for PC-relative branches, we had to
compensate for the size of the current instruction.

This was leading to some branches to not be expanded into bigger
branches, and causing MC to fail.

Author: Dylan McKay

lib/Target/AVR/AVRBranchSelector.cpp

@@ -180,6 +180,9 @@ bool AVRBSel::runOnMachineFunction(MachineFunction &Fn)
           }
         }
 
+        if(isCondBranch(Opc))
+          BranchSize -= 2; // take the size of the current instruction.
+
         assert(!(BranchSize & 1)
                && "BranchSize should have an even number of bytes");
         // If this branch is in range, ignore it.
@@ -214,9 +217,10 @@ bool AVRBSel::runOnMachineFunction(MachineFunction &Fn)
               PI->getOperand(0).setImm(4);
             }
           }
-        }
-        else
-        {
+        } else {
+
+          assert(isCondBranch(Opc) && "opcode should be a conditional branch");
+
           unsigned BrCCOffs;
           // Determine if we can reach the destination block with a rjmp,
           // otherwise a jmp instruction is needed.