Index: llvm/lib/Transforms/Utils/SCCPSolver.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SCCPSolver.cpp
+++ llvm/lib/Transforms/Utils/SCCPSolver.cpp
@@ -208,8 +208,6 @@
 
       if (!Elt)
         LV.markOverdefined(); // Unknown sort of constant.
-      else if (isa<UndefValue>(Elt))
-        ; // Undef values remain unknown.
       else
         LV.markConstant(Elt); // Constants are constant.
     }
@@ -356,8 +354,7 @@
     // We only track the contents of scalar globals.
     if (GV->getValueType()->isSingleValueType()) {
       ValueLatticeElement &IV = TrackedGlobals[GV];
-      if (!isa<UndefValue>(GV->getInitializer()))
-        IV.markConstant(GV->getInitializer());
+      IV.markConstant(GV->getInitializer());
     }
   }
 
@@ -822,9 +819,6 @@
   if (Constant *OpC = getConstant(OpSt)) {
     // Fold the constant as we build.
     Constant *C = ConstantFoldCastOperand(I.getOpcode(), OpC, I.getType(), DL);
-    if (isa<UndefValue>(C))
-      return;
-    // Propagate constant value
     markConstant(&I, C);
   } else if (I.getDestTy()->isIntegerTy()) {
     auto &LV = getValueState(&I);
@@ -961,10 +955,6 @@
 
   if (isConstant(V0State)) {
     Constant *C = ConstantExpr::get(I.getOpcode(), getConstant(V0State));
-
-    // op Y -> undef.
-    if (isa<UndefValue>(C))
-      return;
     return (void)markConstant(IV, &I, C);
   }
 
@@ -999,9 +989,6 @@
     Value *R = simplifyBinOp(I.getOpcode(), V1, V2, SimplifyQuery(DL));
     auto *C = dyn_cast_or_null<Constant>(R);
     if (C) {
-      // X op Y -> undef.
-      if (isa<UndefValue>(C))
-        return;
       // Conservatively assume that the result may be based on operands that may
       // be undef. Note that we use mergeInValue to combine the constant with
       // the existing lattice value for I, as different constants might be found
@@ -1050,6 +1037,7 @@
 
   Constant *C = V1State.getCompare(I.getPredicate(), I.getType(), V2State);
   if (C) {
+    // TODO: getCompare() currently has incorrect handling for unknown/undef.
     if (isa<UndefValue>(C))
       return;
     ValueLatticeElement CV;
@@ -1095,8 +1083,6 @@
   auto Indices = makeArrayRef(Operands.begin() + 1, Operands.end());
   Constant *C =
       ConstantExpr::getGetElementPtr(I.getSourceElementType(), Ptr, Indices);
-  if (isa<UndefValue>(C))
-    return;
   markConstant(&I, C);
 }
 
@@ -1174,11 +1160,8 @@
     }
 
     // Transform load from a constant into a constant if possible.
-    if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, I.getType(), DL)) {
-      if (isa<UndefValue>(C))
-        return;
+    if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, I.getType(), DL))
       return (void)markConstant(IV, &I, C);
-    }
   }
 
   // Fall back to metadata.
@@ -1223,12 +1206,8 @@
 
     // If we can constant fold this, mark the result of the call as a
     // constant.
-    if (Constant *C = ConstantFoldCall(&CB, F, Operands, &GetTLI(*F))) {
-      // call -> undef.
-      if (isa<UndefValue>(C))
-        return;
+    if (Constant *C = ConstantFoldCall(&CB, F, Operands, &GetTLI(*F)))
       return (void)markConstant(&CB, C);
-    }
   }
 
   // Fall back to metadata.
Index: llvm/test/Transforms/SCCP/undef-resolve.ll
===================================================================
--- llvm/test/Transforms/SCCP/undef-resolve.ll
+++ llvm/test/Transforms/SCCP/undef-resolve.ll
@@ -246,8 +246,7 @@
 define i64 @test10() {
 ; CHECK-LABEL: @test10(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[E:%.*]] = extractvalue { i64, i64 } undef, 1
-; CHECK-NEXT:    ret i64 [[E]]
+; CHECK-NEXT:    ret i64 undef
 ;
 entry:
   %e = extractvalue { i64, i64 } undef, 1