Precommit test for SliceIndex method codegen

Add a `codegen-llvm` test to check the number of `icmp` instrucitons
generated for each `SliceIndex` method on the various range types. This
will be updated in the next commit when `SliceIndex::get` is optimized
for `RangeInclusive`.

Author: Kmeakin

tests/codegen-llvm/slice-range-indexing.rs

@@ -0,0 +1,59 @@
+//@ compile-flags: -Copt-level=3
+
+#![crate_type = "lib"]
+
+use std::ops::{Range, RangeFrom, RangeInclusive, RangeTo, RangeToInclusive};
+
+macro_rules! tests {
+    ($range_ty:ty, $get_func_name:ident, $index_func_name:ident) => {
+        #[no_mangle]
+        pub fn $get_func_name(slice: &[u32], range: $range_ty) -> Option<&[u32]> {
+            slice.get(range)
+        }
+
+        #[no_mangle]
+        pub fn $index_func_name(slice: &[u32], range: $range_ty) -> &[u32] {
+            &slice[range]
+        }
+    };
+}
+
+// CHECK-LABEL: @get_range
+// CHECK-COUNT-2: icmp
+// 2 comparisons required: (range.end < slice.len()) && (range.start <= range.end)
+// CHECK-LABEL: @index_range
+// CHECK-COUNT-2: icmp
+// 2 comparisons required: (range.end < slice.len()) && (range.start <= range.end)
+tests!(Range<usize>, get_range, index_range);
+
+// CHECK-LABEL: @get_range_to
+// CHECK-COUNT-1: icmp
+// 1 comparison required: (range.end < slice.len())
+// CHECK-LABEL: @index_range_to
+// CHECK-COUNT-1: icmp
+// 1 comparison required: (range.end < slice.len())
+tests!(RangeTo<usize>, get_range_to, index_range_to);
+
+// CHECK-LABEL: @get_range_from
+// CHECK-COUNT-1: icmp
+// 1 comparison required: (range.start <= slice.len())
+// CHECK-LABEL: @index_range_from
+// CHECK-COUNT-1: icmp
+// 1 comparison required: (range.start <= slice.len())
+tests!(RangeFrom<usize>, get_range_from, index_range_from);
+
+// CHECK-LABEL: @get_range_inclusive
+// CHECK-COUNT-3: icmp
+// 3 comparisons required: (range.end != usize::MAX) && (range.end < slice.len()) && (range.start <= range.end + 1)
+// CHECK-LABEL: @index_range_inclusive
+// CHECK-COUNT-2: icmp
+// 2 comparisons required: (range.end < slice.len()) && (range.start <= range.end + 1)
+tests!(RangeInclusive<usize>, get_range_inclusive, index_range_inclusive);
+
+// CHECK-LABEL: @get_range_to_inclusive
+// CHECK-COUNT-2: icmp
+// 2 comparisons required: (range.end != usize::MAX) && (range.end < slice.len())
+// CHECK-LABEL: @index_range_to_inclusive
+// CHECK-COUNT-1: icmp
+// 1 comparison required: (range.end < slice.len())
+tests!(RangeToInclusive<usize>, get_range_to_inclusive, index_range_to_inclusive);