From e80e577df7ca410eac549da61f9a9fd702dc55ea Mon Sep 17 00:00:00 2001
From: Yap Zhi Heng <yapzhhg@gmail.com>
Date: Wed, 23 Jul 2025 08:24:18 +0800
Subject: 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>
---
 gcc/rust/rust-gcc.cc | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

(limited to 'gcc/rust/rust-gcc.cc')

diff --git a/gcc/rust/rust-gcc.cc b/gcc/rust/rust-gcc.cc
index c5fda5c..0f9ccfb 100644
--- a/gcc/rust/rust-gcc.cc
+++ b/gcc/rust/rust-gcc.cc
@@ -1504,6 +1504,34 @@ array_index_expression (tree array_tree, tree index_tree, location_t location)
   return ret;
 }
 
+// Return an expression representing SLICE[INDEX]
+
+tree
+slice_index_expression (tree slice_tree, tree index_tree, location_t location)
+{
+  if (error_operand_p (slice_tree) || error_operand_p (index_tree))
+    return error_mark_node;
+
+  // A slice is created in TyTyResolvecompile::create_slice_type_record
+  // For example:
+  //   &[i32] is turned directly into a struct { i32* data, usize len };
+  //   [i32] is also turned into struct { i32* data, usize len }
+
+  // it should have RS_DST_FLAG set to 1
+  rust_assert (RS_DST_FLAG_P (TREE_TYPE (slice_tree)));
+
+  tree data_field = struct_field_expression (slice_tree, 0, location);
+  tree data_field_deref = build_fold_indirect_ref_loc (location, data_field);
+
+  tree element_type = TREE_TYPE (data_field_deref);
+  tree data_pointer = TREE_OPERAND (data_field_deref, 0);
+  rust_assert (POINTER_TYPE_P (TREE_TYPE (data_pointer)));
+  tree data_offset_expr
+    = Rust::pointer_offset_expression (data_pointer, index_tree, location);
+
+  return build1_loc (location, INDIRECT_REF, element_type, data_offset_expr);
+}
+
 // Create an expression for a call to FN_EXPR with FN_ARGS.
 tree
 call_expression (tree fn, const std::vector<tree> &fn_args, tree chain_expr,
-- 
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