Add mir-opt test.

Author: cjgillot

tests/mir-opt/slice_filter.rs

@@ -0,0 +1,21 @@
+fn main() {
+    let input = vec![];
+
+    // 1761ms on my machine
+    let _variant_a_result = variant_a(&input);
+
+    //  656ms on my machine
+    let _variant_b_result = variant_b(&input);
+}
+
+
+// EMIT_MIR slice_filter.variant_a-{closure#0}.DestinationPropagation.diff
+pub fn variant_a(input: &[(usize, usize, usize, usize)]) -> usize {
+    input.iter().filter(|(a, b, c, d)| a <= c && d <= b || c <= a && b <= d).count()
+}
+
+
+// EMIT_MIR slice_filter.variant_b-{closure#0}.DestinationPropagation.diff
+pub fn variant_b(input: &[(usize, usize, usize, usize)]) -> usize {
+    input.iter().filter(|&&(a, b, c, d)| a <= c && d <= b || c <= a && b <= d).count()
+}