Add a MIR test ensuring we use an aggregate comparison when matching on a large fixed-length array

Author: jakubadamw

tests/mir-opt/building/match/aggregate_array_eq.array_match.built.after.panic-abort.mir

@@ -0,0 +1,51 @@
+// MIR for `array_match` after built
+
+fn array_match(_1: [u8; 4]) -> bool {
+    debug x => _1;
+    let mut _0: bool;
+    let mut _2: &[u8; 4];
+    let mut _3: bool;
+    scope 1 {
+    }
+
+    bb0: {
+        PlaceMention(_1);
+        _2 = &_1;
+        _3 = <[u8; 4] as PartialEq>::eq(copy _2, const &*b"\x01\x02\x03\x04") -> [return: bb4, unwind: bb8];
+    }
+
+    bb1: {
+        _0 = const false;
+        goto -> bb7;
+    }
+
+    bb2: {
+        falseEdge -> [real: bb6, imaginary: bb1];
+    }
+
+    bb3: {
+        goto -> bb1;
+    }
+
+    bb4: {
+        switchInt(move _3) -> [0: bb1, otherwise: bb2];
+    }
+
+    bb5: {
+        FakeRead(ForMatchedPlace(None), _1);
+        unreachable;
+    }
+
+    bb6: {
+        _0 = const true;
+        goto -> bb7;
+    }
+
+    bb7: {
+        return;
+    }
+
+    bb8 (cleanup): {
+        resume;
+    }
+}

tests/mir-opt/building/match/aggregate_array_eq.array_match.built.after.panic-unwind.mir

@@ -0,0 +1,51 @@
+// MIR for `array_match` after built
+
+fn array_match(_1: [u8; 4]) -> bool {
+    debug x => _1;
+    let mut _0: bool;
+    let mut _2: &[u8; 4];
+    let mut _3: bool;
+    scope 1 {
+    }
+
+    bb0: {
+        PlaceMention(_1);
+        _2 = &_1;
+        _3 = <[u8; 4] as PartialEq>::eq(copy _2, const &*b"\x01\x02\x03\x04") -> [return: bb4, unwind: bb8];
+    }
+
+    bb1: {
+        _0 = const false;
+        goto -> bb7;
+    }
+
+    bb2: {
+        falseEdge -> [real: bb6, imaginary: bb1];
+    }
+
+    bb3: {
+        goto -> bb1;
+    }
+
+    bb4: {
+        switchInt(move _3) -> [0: bb1, otherwise: bb2];
+    }
+
+    bb5: {
+        FakeRead(ForMatchedPlace(None), _1);
+        unreachable;
+    }
+
+    bb6: {
+        _0 = const true;
+        goto -> bb7;
+    }
+
+    bb7: {
+        return;
+    }
+
+    bb8 (cleanup): {
+        resume;
+    }
+}

tests/mir-opt/building/match/aggregate_array_eq.rs

@@ -0,0 +1,15 @@
+// EMIT_MIR_FOR_EACH_PANIC_STRATEGY
+//@ compile-flags: -Zmir-opt-level=0
+
+// Verify that matching against a constant array pattern produces a single
+// `PartialEq::eq` call rather than element-by-element comparisons.
+
+#![crate_type = "lib"]
+
+// EMIT_MIR aggregate_array_eq.array_match.built.after.mir
+pub fn array_match(x: [u8; 4]) -> bool {
+    // CHECK-LABEL: fn array_match(
+    // CHECK: <[u8; 4] as PartialEq>::eq
+    // CHECK-NOT: switchInt(copy _1[
+    matches!(x, [1, 2, 3, 4])
+}