[InstCombine] Add zext nneg test variant for gep of sext add fold (NFC)

Author: nikic

llvm/test/Transforms/InstCombine/array.ll

@@ -72,3 +72,39 @@ entry:
   store i32 %b, ptr %gep
   ret void
 }
+
+define void @test_zext_nneg(ptr %ptr, i32 %a, i32 %b) {
+; CHECK-LABEL: define void @test_zext_nneg(
+; CHECK-SAME: ptr [[PTR:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[A]], 10
+; CHECK-NEXT:    [[IDX:%.*]] = zext nneg i32 [[ADD]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[PTR]], i64 [[IDX]]
+; CHECK-NEXT:    store i32 [[B]], ptr [[GEP]], align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  %add = add nsw i32 %a, 10
+  %idx = zext nneg i32 %add to i64
+  %gep = getelementptr inbounds i32, ptr %ptr, i64 %idx
+  store i32 %b, ptr %gep
+  ret void
+}
+
+define void @test_zext_missing_nneg(ptr %ptr, i32 %a, i32 %b) {
+; CHECK-LABEL: define void @test_zext_missing_nneg(
+; CHECK-SAME: ptr [[PTR:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[A]], 10
+; CHECK-NEXT:    [[IDX:%.*]] = zext i32 [[ADD]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i32, ptr [[PTR]], i64 [[IDX]]
+; CHECK-NEXT:    store i32 [[B]], ptr [[GEP]], align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  %add = add nsw i32 %a, 10
+  %idx = zext i32 %add to i64
+  %gep = getelementptr inbounds i32, ptr %ptr, i64 %idx
+  store i32 %b, ptr %gep
+  ret void
+}