Index: lib/IR/ConstantFold.cpp
===================================================================
--- lib/IR/ConstantFold.cpp
+++ lib/IR/ConstantFold.cpp
@@ -629,6 +629,15 @@
     if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
       if (CE->getOpcode() == Instruction::GetElementPtr &&
           CE->getOperand(0)->isNullValue()) {
+	// FIXME: Looks like getFoldedSizeOf(), getFoldedOffsetOf() and
+	// getFoldedAlignOf() don't handle the case when DestTy is a vector of
+	// pointers yet. We end up in asserts in CastInst::getCastOpcode (see
+	// test/Analysis/ConstantFolding/cast-vector.ll). I've only seen this
+	// happen in one "real" C-code test case, so it does not seem to be an
+	// important optimization to handle vectors here. For now, simply bail
+	// out.
+	if (DestTy->isVectorTy())
+	  return nullptr;
         GEPOperator *GEPO = cast<GEPOperator>(CE);
         Type *Ty = GEPO->getSourceElementType();
         if (CE->getNumOperands() == 2) {
Index: test/Analysis/ConstantFolding/cast-vector.ll
===================================================================
--- /dev/null
+++ test/Analysis/ConstantFolding/cast-vector.ll
@@ -0,0 +1,32 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instsimplify -S | FileCheck %s
+
+; Test constant fold of constant expression GEP used by ptrtoint (the
+; "offsetof-like expression" case).
+; This used to hit an assert due to not supporting vectors in
+; llvm::ConstantFoldCastInstruction when handling ptrtoint.
+define <2 x i16> @test1() {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret <2 x i16> ptrtoint (<2 x i32*> getelementptr ([10 x i32], [10 x i32]* null, <2 x i64> zeroinitializer, <2 x i64> <i64 5, i64 7>) to <2 x i16>)
+;
+entry:
+  %gep = getelementptr inbounds [10 x i32], [10 x i32]* null, i16 0, <2 x i16> <i16 5, i16 7>
+  %vec = ptrtoint <2 x i32*> %gep to <2 x i16>
+  ret <2 x i16> %vec
+}
+
+; Test constant fold of constant expression GEP used by ptrtoint (the
+; "sizeof-like expression" case).
+; This used to hit an assert due to not supporting vectors in
+; llvm::ConstantFoldCastInstruction when handling ptrtoint.
+define <2 x i16> @test2() {
+; CHECK-LABEL: @test2(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret <2 x i16> ptrtoint (<2 x i32*> getelementptr (i32, i32* null, <2 x i64> <i64 5, i64 7>) to <2 x i16>)
+;
+entry:
+  %gep = getelementptr i32, i32* null, <2 x i16> <i16 5, i16 7>
+  %vec = ptrtoint <2 x i32*> %gep to <2 x i16>
+  ret <2 x i16> %vec
+}