Index: llvm/trunk/test/DebugInfo/debugify-bogus-dbg-value.ll
===================================================================
--- llvm/trunk/test/DebugInfo/debugify-bogus-dbg-value.ll
+++ llvm/trunk/test/DebugInfo/debugify-bogus-dbg-value.ll
@@ -0,0 +1,52 @@
+; RUN: opt -check-debugify < %s 2>&1 | FileCheck %s
+
+define <2 x i64> @test-fun(<2 x i64> %A) !dbg !6 {
+  %and = and <2 x i64> %A, <i64 23, i64 42>, !dbg !14
+
+; CHECK: ERROR: dbg.value operand has size 128, but its variable has size 256
+  call void @llvm.dbg.value(metadata <2 x i64> %and, metadata !12, metadata !DIExpression()), !dbg !15
+
+; CHECK: ERROR: dbg.value operand has size 512, but its variable has size 256
+  call void @llvm.dbg.value(metadata <2 x i256> zeroinitializer, metadata !12, metadata !DIExpression()), !dbg !15
+
+; CHECK: ERROR: dbg.value operand has size 8, but its variable has size 256
+  call void @llvm.dbg.value(metadata i8 0, metadata !12, metadata !DIExpression()), !dbg !15
+
+; Assume the debugger implicitly uses the lower 256 bits.
+; CHECK-NOT: ERROR: dbg.value operand has size 512, but its variable has size 256
+  call void @llvm.dbg.value(metadata i512 0, metadata !12, metadata !DIExpression()), !dbg !15
+
+  ret <2 x i64> %and, !dbg !16
+}
+; CHECK: CheckModuleDebugify: FAIL
+
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #0
+
+attributes #0 = { nounwind readnone speculatable }
+
+!llvm.dbg.cu = !{!0}
+!llvm.debugify = !{!3, !4}
+!llvm.module.flags = !{!5}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "/Users/vsk/src/llvm.org-master/llvm/test/DebugInfo/debugify-bogus-dbg-value.ll", directory: "/")
+!2 = !{}
+!3 = !{i32 4}
+!4 = !{i32 3}
+!5 = !{i32 2, !"Debug Info Version", i32 3}
+!6 = distinct !DISubprogram(name: "test-fun", linkageName: "test-fun", scope: null, file: !1, line: 1, type: !7, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: true, unit: !0, retainedNodes: !8)
+!7 = !DISubroutineType(types: !2)
+!8 = !{!9, !11, !12}
+!9 = !DILocalVariable(name: "1", scope: !6, file: !1, line: 1, type: !10)
+!10 = !DIBasicType(name: "ty64", size: 64, encoding: DW_ATE_unsigned)
+!11 = !DILocalVariable(name: "2", scope: !6, file: !1, line: 2, type: !10)
+!12 = !DILocalVariable(name: "3", scope: !6, file: !1, line: 3, type: !13)
+
+; Set the size here to an incorrect value to check that the size diagnostic
+; triggers.
+!13 = !DIBasicType(name: "ty128", size: 256, encoding: DW_ATE_unsigned)
+
+!14 = !DILocation(line: 2, column: 1, scope: !6)
+!15 = !DILocation(line: 3, column: 1, scope: !6)
+!16 = !DILocation(line: 4, column: 1, scope: !6)
Index: llvm/trunk/tools/opt/Debugify.cpp
===================================================================
--- llvm/trunk/tools/opt/Debugify.cpp
+++ llvm/trunk/tools/opt/Debugify.cpp
@@ -40,6 +40,10 @@
 
 raw_ostream &dbg() { return Quiet ? nulls() : errs(); }
 
+uint64_t getAllocSizeInBits(Module &M, Type *Ty) {
+  return Ty->isSized() ? M.getDataLayout().getTypeAllocSizeInBits(Ty) : 0;
+}
+
 bool isFunctionSkipped(Function &F) {
   return F.isDeclaration() || !F.hasExactDefinition();
 }
@@ -71,8 +75,7 @@
   // Get a DIType which corresponds to Ty.
   DenseMap<uint64_t, DIType *> TypeCache;
   auto getCachedDIType = [&](Type *Ty) -> DIType * {
-    uint64_t Size =
-        Ty->isSized() ? M.getDataLayout().getTypeAllocSizeInBits(Ty) : 0;
+    uint64_t Size = getAllocSizeInBits(M, Ty);
     DIType *&DTy = TypeCache[Size];
     if (!DTy) {
       std::string Name = "ty" + utostr(Size);
@@ -163,6 +166,36 @@
   return true;
 }
 
+/// Return true if a mis-sized diagnostic is issued for \p DVI.
+bool diagnoseMisSizedDbgValue(Module &M, DbgValueInst *DVI) {
+  // The size of a dbg.value's value operand should match the size of the
+  // variable it corresponds to.
+  //
+  // TODO: This, along with a check for non-null value operands, should be
+  // promoted to verifier failures.
+  Value *V = DVI->getValue();
+  if (!V)
+    return false;
+
+  // For now, don't try to interpret anything more complicated than an empty
+  // DIExpression. Eventually we should try to handle OP_deref and fragments.
+  if (DVI->getExpression()->getNumElements())
+    return false;
+
+  Type *Ty = V->getType();
+  uint64_t ValueOperandSize = getAllocSizeInBits(M, Ty);
+  uint64_t DbgVarSize = *DVI->getFragmentSizeInBits();
+  bool HasBadSize = Ty->isIntegerTy() ? (ValueOperandSize < DbgVarSize)
+                                      : (ValueOperandSize != DbgVarSize);
+  if (HasBadSize) {
+    dbg() << "ERROR: dbg.value operand has size " << ValueOperandSize
+          << ", but its variable has size " << DbgVarSize << ": ";
+    DVI->print(dbg());
+    dbg() << "\n";
+  }
+  return HasBadSize;
+}
+
 bool checkDebugifyMetadata(Module &M,
                            iterator_range<Module::iterator> Functions,
                            StringRef NameOfWrappedPass, StringRef Banner,
@@ -208,7 +241,7 @@
       HasErrors = true;
     }
 
-    // Find missing variables.
+    // Find missing variables and mis-sized debug values.
     for (Instruction &I : instructions(F)) {
       auto *DVI = dyn_cast<DbgValueInst>(&I);
       if (!DVI)
@@ -217,7 +250,10 @@
       unsigned Var = ~0U;
       (void)to_integer(DVI->getVariable()->getName(), Var, 10);
       assert(Var <= OriginalNumVars && "Unexpected name for DILocalVariable");
-      MissingVars.reset(Var - 1);
+      bool HasBadSize = diagnoseMisSizedDbgValue(M, DVI);
+      if (!HasBadSize)
+        MissingVars.reset(Var - 1);
+      HasErrors |= HasBadSize;
     }
   }