Index: llvm/lib/CodeGen/MachineVerifier.cpp
===================================================================
--- llvm/lib/CodeGen/MachineVerifier.cpp
+++ llvm/lib/CodeGen/MachineVerifier.cpp
@@ -1611,14 +1611,24 @@
     const MCOperandInfo &MCOI = MCID.OpInfo[MONum];
     // Don't check if it's the last operand in a variadic instruction. See,
     // e.g., LDM_RET in the arm back end.
-    if (MO->isReg() &&
-        !(MI->isVariadic() && MONum == MCID.getNumOperands()-1)) {
+    bool IsOptional = (MI->isVariadic() && MONum == MCID.getNumOperands() - 1);
+    if (MO->isReg() && !IsOptional) {
       if (MO->isDef() && !MCOI.isOptionalDef())
         report("Explicit operand marked as def", MO, MONum);
       if (MO->isImplicit())
         report("Explicit operand marked as implicit", MO, MONum);
     }
 
+    // Check that an instruction has register operands only as expected.
+    if (!IsOptional) {
+      if (MCOI.OperandType == MCOI::OPERAND_REGISTER &&
+          (!MO->isReg() && !MO->isFI()))
+        report("Expected a register operand.", MO, MONum);
+      if ((MCOI.OperandType == MCOI::OPERAND_IMMEDIATE ||
+           MCOI.OperandType == MCOI::OPERAND_PCREL) && MO->isReg())
+        report("Expected a non-register operand.", MO, MONum);
+    }
+
     int TiedTo = MCID.getOperandConstraint(MONum, MCOI::TIED_TO);
     if (TiedTo != -1) {
       if (!MO->isReg())
Index: llvm/test/CodeGen/SPARC/fp128.ll
===================================================================
--- llvm/test/CodeGen/SPARC/fp128.ll
+++ llvm/test/CodeGen/SPARC/fp128.ll
@@ -3,6 +3,14 @@
 ; RUN: llc < %s -march=sparc -mattr=-hard-quad-float | FileCheck %s --check-prefix=CHECK --check-prefix=SOFT --check-prefix=BE
 ; RUN: llc < %s -march=sparcel -mattr=-hard-quad-float | FileCheck %s --check-prefix=CHECK --check-prefix=SOFT --check-prefix=EL
 
+# This test currently fails with expensive checks enabled, for more details see
+# https://bugs.llvm.org/show_bug.cgi?id=44091.
+# XFAIL: *
+# *** Bad machine code: Expected a register operand. ***
+# - function:    f128_compare
+# - basic block: %bb.0 entry (0x63f4028)
+# - instruction: CMPrr killed %21:intregs, 0, implicit-def $icc
+# - operand 1:   0
 
 ; CHECK-LABEL: f128_ops:
 ; CHECK:      ldd
Index: llvm/test/MachineVerifier/verify-regops.mir
===================================================================
--- /dev/null
+++ llvm/test/MachineVerifier/verify-regops.mir
@@ -0,0 +1,37 @@
+# RUN: not llc -march=x86 -o - %s -run-pass=none -verify-machineinstrs \
+# RUN:   2>&1 | FileCheck %s
+# REQUIRES: x86-registered-target
+#
+# Check that MachineVerifier catches corrupt operands where MO->isReg()
+# returns true, but the descriptor says it should be an OPERAND_IMMEDIATE or
+# OPERAND_PCREL. Conversely, if MO->isReg() (and MO->isFI()) returns false,
+# check that not an OPERAND_REGISTER is expected.
+
+# CHECK-LABEL: fun
+
+# CHECK: *** Bad machine code: Expected a register operand. ***
+# CHECK: - instruction: %1:gr32 = XOR32rm -1, %fixed-stack.1, 1, $noreg, 0, $noreg, implicit-def dead $eflags :: (load 4 from %fixed-stack.1, align 8)
+# CHECK: - operand 1:   -1
+
+# CHECK: *** Bad machine code: Expected a non-register operand. ***
+# CHECK: - instruction: %2:gr32 = OR32ri %1:gr32(tied-def 0), %0:gr32, implicit-def dead $eflags
+# CHECK: - operand 2:   %0:gr32
+
+
+name:            fun
+tracksRegLiveness: true
+fixedStack:
+  - { id: 1, offset: 8, size: 4, alignment: 8, isImmutable: true }
+  - { id: 3, size: 4, alignment: 16, isImmutable: true }
+body:             |
+  bb.0:
+    %0:gr32 = MOV32rm %fixed-stack.3, 1, $noreg, 0, $noreg :: (load 4 from %fixed-stack.3, align 16)
+    ; Was: %1:gr32 = XOR32rm %0, %fixed-stack.1, 1, $noreg, 0, $noreg, implicit-def dead $eflags :: (load 4 from %fixed-stack.1, align 8)
+    %1:gr32 = XOR32rm -1, %fixed-stack.1, 1, $noreg, 0, $noreg, implicit-def dead $eflags :: (load 4 from %fixed-stack.1, align 8)
+    ; Was: %2:gr32 = OR32ri %1, -256, implicit-def dead $eflags
+    %2:gr32 = OR32ri %1, %0, implicit-def dead $eflags
+    %3:gr32 = MOV32ri -1
+    $eax = COPY %2
+    $edx = COPY %3
+    RET 0, $eax, $edx
+...