diff --git a/llvm/lib/CodeGen/MachineDebugify.cpp b/llvm/lib/CodeGen/MachineDebugify.cpp
--- a/llvm/lib/CodeGen/MachineDebugify.cpp
+++ b/llvm/lib/CodeGen/MachineDebugify.cpp
@@ -153,10 +153,15 @@
       NMD->setOperand(Idx, MDNode::get(Ctx, ValueAsMetadata::getConstant(
                                                 ConstantInt::get(Int32Ty, N))));
     };
+    auto getDebugifyOperand = [&](unsigned Idx) {
+      return mdconst::extract<ConstantInt>(NMD->getOperand(Idx)->getOperand(0))
+          ->getZExtValue();
+    };
     // Set number of lines.
     setDebugifyOperand(0, NextLine - 1);
     // Set number of variables.
-    setDebugifyOperand(1, VarSet.size());
+    auto OldNumVars = getDebugifyOperand(1);
+    setDebugifyOperand(1, OldNumVars + VarSet.size());
   }
 
   return true;
@@ -166,6 +171,9 @@
 /// legacy module pass manager.
 struct DebugifyMachineModule : public ModulePass {
   bool runOnModule(Module &M) override {
+    // We will insert new debugify metadata, so erasing the old one.
+    assert(!M.getNamedMetadata("llvm.mir.debugify") &&
+           "llvm.mir.debugify metadata already exists! Strip it first");
     MachineModuleInfo &MMI =
         getAnalysis<MachineModuleInfoWrapperPass>().getMMI();
     return applyDebugifyMetadata(
diff --git a/llvm/test/CodeGen/Generic/MIRDebugify/multifunction-module.mir b/llvm/test/CodeGen/Generic/MIRDebugify/multifunction-module.mir
--- a/llvm/test/CodeGen/Generic/MIRDebugify/multifunction-module.mir
+++ b/llvm/test/CodeGen/Generic/MIRDebugify/multifunction-module.mir
@@ -1,6 +1,7 @@
-# RUN: llc -run-pass=mir-debugify,mir-check-debugify %s
+# RUN: llc -run-pass=mir-debugify,mir-check-debugify -o - %s 2>&1 | FileCheck %s
 
-# XFAIL: *
+# CHECK: Machine IR debug info check: PASS
+# CHECK-NOT: Assertion `Var <= NumVars && "Unexpected name for DILocalVariable"'
 
 --- |
   define i32 @foo(i32 %a0, i32 %a1, i32 %a2, i32 %a3) {
@@ -20,145 +21,27 @@
 ...
 ---
 name:            foo
-alignment:       16
-exposesReturnsTwice: false
-legalized:       false
-regBankSelected: false
-selected:        false
-failedISel:      false
-tracksRegLiveness: true
-hasWinCFI:       false
-callsEHReturn:   false
-callsUnwindInit: false
-hasEHCatchret:   false
-hasEHScopes:     false
-hasEHFunclets:   false
-failsVerification: false
-tracksDebugUserValues: false
-registers:
-  - { id: 0, class: _, preferred-register: '' }
-  - { id: 1, class: _, preferred-register: '' }
-  - { id: 2, class: _, preferred-register: '' }
-  - { id: 3, class: _, preferred-register: '' }
-  - { id: 4, class: _, preferred-register: '' }
-  - { id: 5, class: _, preferred-register: '' }
-  - { id: 6, class: _, preferred-register: '' }
-liveins:
-  - { reg: '$edi', virtual-reg: '' }
-  - { reg: '$esi', virtual-reg: '' }
-  - { reg: '$edx', virtual-reg: '' }
-  - { reg: '$ecx', virtual-reg: '' }
-frameInfo:
-  isFrameAddressTaken: false
-  isReturnAddressTaken: false
-  hasStackMap:     false
-  hasPatchPoint:   false
-  stackSize:       0
-  offsetAdjustment: 0
-  maxAlignment:    1
-  adjustsStack:    false
-  hasCalls:        false
-  stackProtector:  ''
-  functionContext: ''
-  maxCallFrameSize: 4294967295
-  cvBytesOfCalleeSavedRegisters: 0
-  hasOpaqueSPAdjustment: false
-  hasVAStart:      false
-  hasMustTailInVarArgFunc: false
-  hasTailCall:     false
-  localFrameSize:  0
-  savePoint:       ''
-  restorePoint:    ''
-fixedStack:      []
-stack:           []
-callSites:       []
-debugValueSubstitutions: []
-constants:       []
-machineFunctionInfo: {}
 body:             |
   bb.1 (%ir-block.0):
-    liveins: $ecx, $edi, $edx, $esi
-
-    %0:_(s32) = COPY $edi
-    %1:_(s32) = COPY $esi
-    %2:_(s32) = COPY $edx
-    %3:_(s32) = COPY $ecx
+    %0:_(s32) = IMPLICIT_DEF
+    %1:_(s32) = IMPLICIT_DEF
+    %2:_(s32) = IMPLICIT_DEF
+    %3:_(s32) = IMPLICIT_DEF
     %4:_(s32) = G_ADD %0, %1
     %5:_(s32) = G_ADD %4, %2
     %6:_(s32) = G_ADD %5, %3
-    $eax = COPY %6(s32)
-    RET 0, implicit $eax
 
 ...
 ---
 name:            bar
-alignment:       16
-exposesReturnsTwice: false
-legalized:       false
-regBankSelected: false
-selected:        false
-failedISel:      false
-tracksRegLiveness: true
-hasWinCFI:       false
-callsEHReturn:   false
-callsUnwindInit: false
-hasEHCatchret:   false
-hasEHScopes:     false
-hasEHFunclets:   false
-failsVerification: false
-tracksDebugUserValues: false
-registers:
-  - { id: 0, class: _, preferred-register: '' }
-  - { id: 1, class: _, preferred-register: '' }
-  - { id: 2, class: _, preferred-register: '' }
-  - { id: 3, class: _, preferred-register: '' }
-  - { id: 4, class: _, preferred-register: '' }
-  - { id: 5, class: _, preferred-register: '' }
-  - { id: 6, class: _, preferred-register: '' }
-liveins:
-  - { reg: '$edi', virtual-reg: '' }
-  - { reg: '$esi', virtual-reg: '' }
-  - { reg: '$edx', virtual-reg: '' }
-  - { reg: '$ecx', virtual-reg: '' }
-frameInfo:
-  isFrameAddressTaken: false
-  isReturnAddressTaken: false
-  hasStackMap:     false
-  hasPatchPoint:   false
-  stackSize:       0
-  offsetAdjustment: 0
-  maxAlignment:    1
-  adjustsStack:    false
-  hasCalls:        false
-  stackProtector:  ''
-  functionContext: ''
-  maxCallFrameSize: 4294967295
-  cvBytesOfCalleeSavedRegisters: 0
-  hasOpaqueSPAdjustment: false
-  hasVAStart:      false
-  hasMustTailInVarArgFunc: false
-  hasTailCall:     false
-  localFrameSize:  0
-  savePoint:       ''
-  restorePoint:    ''
-fixedStack:      []
-stack:           []
-callSites:       []
-debugValueSubstitutions: []
-constants:       []
-machineFunctionInfo: {}
 body:             |
   bb.1 (%ir-block.0):
-    liveins: $ecx, $edi, $edx, $esi
-
-    %0:_(s32) = COPY $edi
-    %1:_(s32) = COPY $esi
-    %2:_(s32) = COPY $edx
-    %3:_(s32) = COPY $ecx
+    %0:_(s32) = IMPLICIT_DEF
+    %1:_(s32) = IMPLICIT_DEF
+    %2:_(s32) = IMPLICIT_DEF
+    %3:_(s32) = IMPLICIT_DEF
     %4:_(s32) = G_ADD %0, %1
     %5:_(s32) = G_ADD %2, %4
     %6:_(s32) = G_ADD %5, %3
-    $eax = COPY %6(s32)
-    RET 0, implicit $eax
 
 ...