Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -650,7 +650,8 @@
     } else if (match(Arg, m_c_ICmp(Pred, m_Shl(m_V, m_ConstantInt(C)),
                                    m_Value(A))) &&
                Pred == ICmpInst::ICMP_EQ &&
-               isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+               isValidAssumeForContext(I, Q.CxtI, Q.DT) &&
+               C->getZExtValue() < BitWidth) {
       KnownBits RHSKnown(BitWidth);
       computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
       // For those bits in RHS that are known, we can propagate them to known
@@ -663,7 +664,8 @@
     } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_Shl(m_V, m_ConstantInt(C))),
                                    m_Value(A))) &&
                Pred == ICmpInst::ICMP_EQ &&
-               isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+               isValidAssumeForContext(I, Q.CxtI, Q.DT) &&
+               C->getZExtValue() < BitWidth) {
       KnownBits RHSKnown(BitWidth);
       computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
       // For those bits in RHS that are known, we can propagate them inverted
@@ -677,7 +679,8 @@
                      m_c_ICmp(Pred, m_Shr(m_V, m_ConstantInt(C)),
                               m_Value(A))) &&
                Pred == ICmpInst::ICMP_EQ &&
-               isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+               isValidAssumeForContext(I, Q.CxtI, Q.DT) &&
+               C->getZExtValue() < BitWidth) {
       KnownBits RHSKnown(BitWidth);
       computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
       // For those bits in RHS that are known, we can propagate them to known
@@ -688,7 +691,8 @@
     } else if (match(Arg, m_c_ICmp(Pred, m_Not(m_Shr(m_V, m_ConstantInt(C))),
                                    m_Value(A))) &&
                Pred == ICmpInst::ICMP_EQ &&
-               isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
+               isValidAssumeForContext(I, Q.CxtI, Q.DT) &&
+               C->getZExtValue() < BitWidth) {
       KnownBits RHSKnown(BitWidth);
       computeKnownBits(A, RHSKnown, Depth+1, Query(Q, I));
       // For those bits in RHS that are known, we can propagate them inverted
Index: test/Transforms/InstCombine/out-of-bounds-indexes.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/out-of-bounds-indexes.ll
@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+; Check that we don't crash on unreasonable constant indexes
+
+define i32 @test1(i32 %a, i1 %x, i1 %y) {
+; CHECK-LABEL: @test2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[AND1:%.*]] = and i32 [[A:%.*]], 3
+; CHECK-NEXT:    tail call void @llvm.assume(i1 false)
+; CHECK-NEXT:    ret i32 [[AND1]]
+;
+entry:
+  %and1 = and i32 %a, 3
+  %B = lshr i32 %and1, -2147483648
+  %cmp = icmp eq i32 %B, 1
+  tail call void @llvm.assume(i1 %cmp)
+  ret i32 %and1
+}
+
+declare void @llvm.assume(i1)
+