gccrs: Implement compilation for SlicePattern against SliceType scrutinee

006t.original output from compiling testsuite/rust/compile/match-slicepattern-slice.rs:

...
  RUSTTMP.3 = slice;
  if (RUSTTMP.3.len == 1 && *(RUSTTMP.3.data + 0 * 4) == 1)
    {
      {
                struct () RUSTTMP.4;
        {

        }
        goto <D.129>;
      }
    }
  if (RUSTTMP.3.len == 2 && *(RUSTTMP.3.data + 1 * 4) == 2)
    {
      {
                struct () RUSTTMP.5;
        {

        }
        goto <D.129>;
      }
    }
  if (1)
    {
      {
                struct () RUSTTMP.6;
        {

        }
        goto <D.129>;
      }
    }
  <D.129>:;
...

gcc/rust/ChangeLog:

	* rust-backend.h: New slice_index_expression function.
	* rust-gcc.cc: Implementation of slice_index_expression to generate tree node for
		accessing slice elements.
	* backend/rust-compile-pattern.cc: Implement SlicePattern check expression & binding
		compilation against SliceType scrutinee.

Signed-off-by: Yap Zhi Heng <yapzhhg@gmail.com>

2 files changed, 34 insertions, 0 deletions

diff --git a/gcc/testsuite/rust/compile/match-slicepattern-slice.rs b/gcc/testsuite/rust/compile/match-slicepattern-slice.rs
new file mode 100644
index 0000000..cc33d93
--- /dev/null
+++ b/gcc/testsuite/rust/compile/match-slicepattern-slice.rs
@@ -0,0 +1,10 @@
+fn main() {
+    let arr = [1, 2];
+    let slice: &[i32] = &arr;
+
+    match slice {
+        [1] => {},
+        [_, 2] => {},
+        _ => {}
+    }
+}
\ No newline at end of file
diff --git a/gcc/testsuite/rust/execute/torture/match-slicepattern-slice-1.rs b/gcc/testsuite/rust/execute/torture/match-slicepattern-slice-1.rs
new file mode 100644
index 0000000..3ed0b644
--- /dev/null
+++ b/gcc/testsuite/rust/execute/torture/match-slicepattern-slice-1.rs
@@ -0,0 +1,24 @@
+// { dg-output "correct\r*" }
+extern "C" {
+    fn puts(s: *const i8);
+}
+
+fn main() -> i32 {
+    let arr = [0, 1];
+    let a: &[i32] = &arr;
+    let mut ret = 1;
+
+    match a {
+        [0, 0] => {
+            /* should not take this path */
+            unsafe { puts("wrong\0" as *const str as *const i8) }
+        },
+        [0, b] => {
+            ret -= b;
+            unsafe { puts("correct\0" as *const str as *const i8) }
+        },
+        _ => {}
+    }
+
+    ret
+}