Index: lib/Target/AArch64/AArch64FastISel.cpp
===================================================================
--- lib/Target/AArch64/AArch64FastISel.cpp
+++ lib/Target/AArch64/AArch64FastISel.cpp
@@ -4832,7 +4832,7 @@
   for (auto OI = std::next(I->op_begin()), E = I->op_end(); OI != E; ++OI) {
     const Value *Idx = *OI;
     if (auto *StTy = dyn_cast<StructType>(Ty)) {
-      unsigned Field = cast<ConstantInt>(Idx)->getZExtValue();
+      uint64_t Field = cast<ConstantInt>(Idx)->getZExtValue();
       // N = N + Offset
       if (Field)
         TotalOffs += DL.getStructLayout(StTy)->getElementOffset(Field);
@@ -4844,8 +4844,8 @@
         if (CI->isZero())
           continue;
         // N = N + Offset
-        TotalOffs +=
-            DL.getTypeAllocSize(Ty) * cast<ConstantInt>(CI)->getSExtValue();
+        uint64_t IdxN = CI->getValue().sextOrTrunc(64).getSExtValue();
+        TotalOffs += DL.getTypeAllocSize(Ty) * IdxN;
         continue;
       }
       if (TotalOffs) {
Index: test/CodeGen/AArch64/getelementptr.ll
===================================================================
--- /dev/null
+++ test/CodeGen/AArch64/getelementptr.ll
@@ -0,0 +1,77 @@
+; RUN: llc < %s -O0 -march=arm64
+; RUN: llc < %s -O2 -march=arm64
+
+; Test big index trunc to pointer size:
+
+define i8* @test_trunc65(i8* %ptr) nounwind {
+; CHECK-LABEL: test_trunc65
+; CHECK: 3
+  %d = getelementptr i8, i8* %ptr, i65 18446744073709551619 ; 2^64 + 3
+  ret i8* %d
+}
+
+define i8* @test_trunc128(i8* %ptr) nounwind {
+; CHECK-LABEL: test_trunc128
+; CHECK: 5
+  %d = getelementptr i8, i8* %ptr, i128 18446744073709551621 ; 2^64 + 5
+  ret i8* %d
+}
+
+define i8* @test_trunc160(i8* %ptr) nounwind {
+; CHECK-LABEL: test_trunc160
+; CHECK: 8
+  %d = getelementptr i8, i8* %ptr, i160 18446744073709551624 ; 2^64 + 8
+  ret i8* %d
+}
+
+define i8* @test_trunc256(i8* %ptr) nounwind {
+; CHECK-LABEL: test_trunc256
+; CHECK: 13
+  %d = getelementptr i8, i8* %ptr, i256 18446744073709551629 ; 2^64 + 13
+  ret i8* %d
+}
+
+define i8* @test_trunc2048(i8* %ptr) nounwind {
+; CHECK-LABEL: test_trunc2048
+; CHECK: 21
+  %d = getelementptr i8, i8* %ptr, i2048 18446744073709551637 ; 2^64 + 21
+  ret i8* %d
+}
+
+
+; Test small index sext to pointer size
+
+define i8* @test_sext3(i8* %ptr) nounwind {
+; CHECK-LABEL: test_sext3
+; CHECK: -3
+  %d = getelementptr i8, i8* %ptr, i3 -3
+  ret i8* %d
+}
+
+define i8* @test_sext5(i8* %ptr) nounwind {
+; CHECK-LABEL: test_sext5
+; CHECK: -5
+  %d = getelementptr i8, i8* %ptr, i5 -5
+  ret i8* %d
+}
+
+define i8* @test_sext8(i8* %ptr) nounwind {
+; CHECK-LABEL: test_sext8
+; CHECK: -8
+  %d = getelementptr i8, i8* %ptr, i8 -8
+  ret i8* %d
+}
+
+define i8* @test_sext13(i8* %ptr) nounwind {
+; CHECK-LABEL: test_sext13
+; CHECK: -13
+  %d = getelementptr i8, i8* %ptr, i8 -13
+  ret i8* %d
+}
+
+define i8* @test_sext16(i8* %ptr) nounwind {
+; CHECK-LABEL: test_sext16
+; CHECK: -21
+  %d = getelementptr i8, i8* %ptr, i8 -21
+  ret i8* %d
+}