Allow trailing physreg RegisterSDNode operands on non-variadic instructions.

Also allow trailing register mask operands on non-variadic both
MachineSDNodes and MachineInstrs.

The extra physreg RegisterSDNode operands are added to the MI as
<imp-use> operands. This makes it possible to have non-variadic call
instructions.

Call and return instructions really are non-variadic, the argument
registers should only be used implicitly - they are not part of the
encoding.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159727 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/MachineInstr.cpp b/lib/CodeGen/MachineInstr.cpp
index 5d16c20..85b5e39 100644
--- a/lib/CodeGen/MachineInstr.cpp
+++ b/lib/CodeGen/MachineInstr.cpp
@@ -660,7 +660,9 @@
 
   // OpNo now points as the desired insertion point.  Unless this is a variadic
   // instruction, only implicit regs are allowed beyond MCID->getNumOperands().
-  assert((isImpReg || MCID->isVariadic() || OpNo < MCID->getNumOperands()) &&
+  // RegMask operands go between the explicit and implicit operands.
+  assert((isImpReg || Op.isRegMask() || MCID->isVariadic() ||
+          OpNo < MCID->getNumOperands()) &&
          "Trying to add an operand to a machine instr that is already done!");
 
   // All operands from OpNo have been removed from RegInfo.  If the Operands