Index: llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1192,6 +1192,12 @@
         return nullptr;
       }
       if (I->getOperand(i)->getType()->isVectorTy()) {
+        // Don't mess with all zeros constants. There are other combines
+        // that consider an all zero constant index canonical.
+        // FIXME: Should we skip all constant splats?
+        if (isa<Constant>(I->getOperand(i)) &&
+            cast<Constant>(I->getOperand(i))->isNullValue())
+          continue;
         APInt UndefEltsOp(VWidth, 0);
         simplifyAndSetOp(I, i, DemandedElts, UndefEltsOp);
         UndefElts |= UndefEltsOp;
Index: llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
===================================================================
--- llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
+++ llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
@@ -651,3 +651,23 @@
   %r = extractelement <2 x i32*> %w, i32 0
   ret i32* %r
 }
+
+@global = external global [0 x i32], align 4
+
+; The global here has size 0 so InstCombine would like the first index to be
+; zeroinitializer, but SimplifyDemandedVectorElts was trying to turn that index into
+; <i64 0, i64 undef, i64 undef, i64 undef>. SimplifyDemandedVectorElts has been told
+; to leave a zeroinitializer indices alone.
+define i32* @ham(<4 x i64> %arg, i64 %arg1) {
+; CHECK-LABEL: @ham(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[TMP:%.*]] = getelementptr inbounds [0 x i32], <4 x [0 x i32]*> <[0 x i32]* @global, [0 x i32]* undef, [0 x i32]* undef, [0 x i32]* undef>, <4 x i64> zeroinitializer, <4 x i64> [[ARG:%.*]]
+; CHECK-NEXT:    [[TMP2:%.*]] = extractelement <4 x i32*> [[TMP]], i64 0
+; CHECK-NEXT:    ret i32* [[TMP2]]
+;
+bb:
+  %tmp = getelementptr inbounds [0 x i32], <4 x [0 x i32]*> <[0 x i32]* @global, [0 x i32]* @global, [0 x i32]* @global, [0 x i32]* @global>, <4 x i64> zeroinitializer, <4 x i64> %arg
+  %tmp2 = extractelement <4 x i32*> %tmp, i64 0
+  ret i32* %tmp2
+}
+