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{
    "id": 2223276,
    "url": "http://patchwork.ozlabs.org/api/1.2/patches/2223276/?format=api",
    "web_url": "http://patchwork.ozlabs.org/project/gcc/patch/20260414231905.191063-10-arthur.cohen@embecosm.com/",
    "project": {
        "id": 17,
        "url": "http://patchwork.ozlabs.org/api/1.2/projects/17/?format=api",
        "name": "GNU Compiler Collection",
        "link_name": "gcc",
        "list_id": "gcc-patches.gcc.gnu.org",
        "list_email": "gcc-patches@gcc.gnu.org",
        "web_url": null,
        "scm_url": null,
        "webscm_url": null,
        "list_archive_url": "",
        "list_archive_url_format": "",
        "commit_url_format": ""
    },
    "msgid": "<20260414231905.191063-10-arthur.cohen@embecosm.com>",
    "list_archive_url": null,
    "date": "2026-04-14T23:18:31",
    "name": "[COMMITTED,10/43] gccrs: intrinsic: Add ctlz and ctlz_nonzero intrinsics",
    "commit_ref": null,
    "pull_url": null,
    "state": "new",
    "archived": false,
    "hash": "4e61697f67713b6c7da0d03bd6c4edd1a1011ae6",
    "submitter": {
        "id": 83476,
        "url": "http://patchwork.ozlabs.org/api/1.2/people/83476/?format=api",
        "name": "Arthur Cohen",
        "email": "arthur.cohen@embecosm.com"
    },
    "delegate": null,
    "mbox": "http://patchwork.ozlabs.org/project/gcc/patch/20260414231905.191063-10-arthur.cohen@embecosm.com/mbox/",
    "series": [
        {
            "id": 499900,
            "url": "http://patchwork.ozlabs.org/api/1.2/series/499900/?format=api",
            "web_url": "http://patchwork.ozlabs.org/project/gcc/list/?series=499900",
            "date": "2026-04-14T23:18:24",
            "name": "[COMMITTED,01/43] gccrs: testsuite:Add a testcase for setup_associated_types",
            "version": 1,
            "mbox": "http://patchwork.ozlabs.org/series/499900/mbox/"
        }
    ],
    "comments": "http://patchwork.ozlabs.org/api/patches/2223276/comments/",
    "check": "pending",
    "checks": "http://patchwork.ozlabs.org/api/patches/2223276/checks/",
    "tags": {},
    "related": [],
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        "From": "arthur.cohen@embecosm.com",
        "To": "gcc-patches@gcc.gnu.org",
        "Cc": "gcc-rust@gcc.gnu.org,\n\tMohamed Ali <mohmedali1462005@gmail.com>",
        "Subject": "[COMMITTED 10/43] gccrs: intrinsic: Add ctlz and ctlz_nonzero\n intrinsics",
        "Date": "Wed, 15 Apr 2026 01:18:31 +0200",
        "Message-ID": "<20260414231905.191063-10-arthur.cohen@embecosm.com>",
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    },
    "content": "From: Mohamed Ali <mohmedali1462005@gmail.com>\n\nThis commit introduces the `ctlz` and `ctlz_nonzero` intrinsics for counting leading zeros\nin integer types.\nThe implementation includes handlers for both intrinsics, which validate input types and utilize\nGCC built-ins for the actual computation.\n\nAddresses: Rust-GCC#658\n\ngcc/rust/ChangeLog:\n\n\t* backend/rust-compile-intrinsic.cc: Register ctlz and ctlz_nonzero intrinsics.\n\t* backend/rust-intrinsic-handlers.cc (ctlz_handler): Implement ctlz_handler.\n\t(ctlz_nonzero_handler): Implement ctlz_nonzero_handler.\n\t* backend/rust-intrinsic-handlers.h (ctlz_handler): Add decl for ctlz_handler.\n\t(ctlz_nonzero_handler): Add decl for ctlz_nonzero_handler.\n\t* util/rust-intrinsic-values.h: map ctlz_nonzero to its name.\n\ngcc/testsuite/ChangeLog:\n\n\t* rust/compile/ctlz.rs: New test.\n\t* rust/compile/ctlz_nonzero.rs: New test.\n\t* rust/execute/torture/ctlz.rs: New test.\n\t* rust/execute/torture/ctlz_nonzero.rs: New test.\n\nSigned-off-by: Mohamed Ali <mohmedali1462005@gmail.com>\n---\n gcc/rust/backend/rust-compile-intrinsic.cc    |   4 +-\n gcc/rust/backend/rust-intrinsic-handlers.cc   | 157 ++++++++++++++++++\n gcc/rust/backend/rust-intrinsic-handlers.h    |   2 +\n gcc/rust/util/rust-intrinsic-values.h         |   1 +\n gcc/testsuite/rust/compile/ctlz.rs            |  17 ++\n gcc/testsuite/rust/compile/ctlz_nonzero.rs    |  19 +++\n gcc/testsuite/rust/execute/torture/ctlz.rs    |  56 +++++++\n .../rust/execute/torture/ctlz_nonzero.rs      |  46 +++++\n 8 files changed, 301 insertions(+), 1 deletion(-)\n create mode 100644 gcc/testsuite/rust/compile/ctlz.rs\n create mode 100644 gcc/testsuite/rust/compile/ctlz_nonzero.rs\n create mode 100644 gcc/testsuite/rust/execute/torture/ctlz.rs\n create mode 100644 gcc/testsuite/rust/execute/torture/ctlz_nonzero.rs",
    "diff": "diff --git a/gcc/rust/backend/rust-compile-intrinsic.cc b/gcc/rust/backend/rust-compile-intrinsic.cc\nindex a4924542da3..9263883e9a5 100644\n--- a/gcc/rust/backend/rust-compile-intrinsic.cc\n+++ b/gcc/rust/backend/rust-compile-intrinsic.cc\n@@ -68,7 +68,9 @@ static const std::map<std::string, handlers::HandlerBuilder> generic_intrinsics\n      {IValue::CATCH_UNWIND, handlers::try_handler (true)},\n      {IValue::DISCRIMINANT_VALUE, handlers::discriminant_value},\n      {IValue::VARIANT_COUNT, handlers::variant_count},\n-     {IValue::BSWAP, handlers::bswap_handler}};\n+     {IValue::BSWAP, handlers::bswap_handler},\n+     {IValue::CTLZ, handlers::ctlz_handler},\n+     {IValue::CTLZ_NONZERO, handlers::ctlz_nonzero_handler}};\n \n Intrinsics::Intrinsics (Context *ctx) : ctx (ctx) {}\n \ndiff --git a/gcc/rust/backend/rust-intrinsic-handlers.cc b/gcc/rust/backend/rust-intrinsic-handlers.cc\nindex 5c7854ce8de..eb86c8ad959 100644\n--- a/gcc/rust/backend/rust-intrinsic-handlers.cc\n+++ b/gcc/rust/backend/rust-intrinsic-handlers.cc\n@@ -748,6 +748,151 @@ atomic_load (Context *ctx, TyTy::FnType *fntype, int ordering)\n   return fndecl;\n }\n \n+// Shared inner implementation for ctlz and ctlz_nonzero.\n+//\n+// nonzero=false → ctlz: ctlz(0) is well-defined in Rust and must return\n+//   bit_size, but __builtin_clz*(0) is undefined behaviour in C, so an\n+//   explicit arg==0 guard is emitted.\n+//\n+// nonzero=true → ctlz_nonzero: the caller guarantees arg != 0 (passing 0\n+//   is immediate UB in Rust), so the zero guard is omitted entirely.\n+static tree\n+ctlz_handler (Context *ctx, TyTy::FnType *fntype, bool nonzero)\n+{\n+  rust_assert (fntype->get_params ().size () == 1);\n+\n+  tree lookup = NULL_TREE;\n+  if (check_for_cached_intrinsic (ctx, fntype, &lookup))\n+    return lookup;\n+\n+  auto fndecl = compile_intrinsic_function (ctx, fntype);\n+\n+  std::vector<Bvariable *> param_vars;\n+  compile_fn_params (ctx, fntype, fndecl, &param_vars);\n+\n+  auto arg_param = param_vars.at (0);\n+  if (!Backend::function_set_parameters (fndecl, param_vars))\n+    return error_mark_node;\n+\n+  rust_assert (fntype->get_num_substitutions () == 1);\n+  auto *monomorphized_type\n+    = fntype->get_substs ().at (0).get_param_ty ()->resolve ();\n+  if (!check_for_basic_integer_type (\"ctlz\", fntype->get_locus (),\n+\t\t\t\t     monomorphized_type))\n+    return error_mark_node;\n+\n+  enter_intrinsic_block (ctx, fndecl);\n+\n+  // BUILTIN ctlz FN BODY BEGIN\n+  auto locus = fntype->get_locus ();\n+  auto arg_expr = Backend::var_expression (arg_param, locus);\n+  tree arg_type = TREE_TYPE (arg_expr);\n+  unsigned bit_size = TYPE_PRECISION (arg_type);\n+\n+  // Convert signed types to their same-width unsigned equivalent before\n+  // widening.  Without this, widening a signed type sign-extends it.\n+  // For example, i8(-1) = 0xFF widened to u32 gives 0xFFFFFFFF, so\n+  // __builtin_clz(0xFFFFFFFF) = 0, then 0 - diff(24) = -24.\n+  // Converting to u8 first gives 0xFF → 0x000000FF (zero-extended), so\n+  // __builtin_clz(0x000000FF) = 24, then 24 - 24 = 0.\n+  tree unsigned_type\n+    = !TYPE_UNSIGNED (arg_type) ? unsigned_type_for (arg_type) : arg_type;\n+  tree unsigned_arg = fold_convert (unsigned_type, arg_expr);\n+\n+  // Pick the narrowest GCC clz builtin whose operand type is wide enough to\n+  // hold bit_size bits.  diff records how many extra leading zeros the builtin\n+  // will count due to the width difference and is subtracted from the result.\n+  //\n+  // Example: ctlz(1u8) bit_size=8, int_prec=32, diff=24.\n+  //   __builtin_clz(1u) returns 31 (counts from bit 31 down to bit 0).\n+  //   31 - 24 = 7, which is the correct answer for an 8-bit value.\n+  //\n+  // TODO: 128-bit integers are not yet handled.\n+  unsigned int_prec = TYPE_PRECISION (unsigned_type_node);\n+  unsigned long_prec = TYPE_PRECISION (long_unsigned_type_node);\n+  unsigned longlong_prec = TYPE_PRECISION (long_long_unsigned_type_node);\n+\n+  const char *builtin_name = nullptr;\n+  tree cast_type = NULL_TREE;\n+  int diff = 0;\n+\n+  if (bit_size <= int_prec)\n+    {\n+      // Fits in unsigned int: covers 8/16/32-bit integers on most targets.\n+      builtin_name = \"__builtin_clz\";\n+      cast_type = unsigned_type_node;\n+      diff = static_cast<int> (int_prec - bit_size);\n+    }\n+  else if (bit_size <= long_prec)\n+    {\n+      // Fits in unsigned long but not unsigned int.\n+      builtin_name = \"__builtin_clzl\";\n+      cast_type = long_unsigned_type_node;\n+      diff = static_cast<int> (long_prec - bit_size);\n+    }\n+  else if (bit_size <= longlong_prec)\n+    {\n+      // Fits in unsigned long long but not unsigned long.\n+      builtin_name = \"__builtin_clzll\";\n+      cast_type = long_long_unsigned_type_node;\n+      diff = static_cast<int> (longlong_prec - bit_size);\n+    }\n+  else\n+    {\n+      rust_sorry_at (locus, \"ctlz for %u-bit integers is not yet implemented\",\n+\t\t     bit_size);\n+      return error_mark_node;\n+    }\n+\n+  // Widen the unsigned arg to the chosen builtin's operand type, call it,\n+  // then subtract the padding bits.  diff == 0 means the Rust type exactly\n+  // matches the builtin's operand width, so the subtraction is skipped.\n+  tree call_arg = fold_convert (cast_type, unsigned_arg);\n+\n+  tree builtin_decl = error_mark_node;\n+  BuiltinsContext::get ().lookup_simple_builtin (builtin_name, &builtin_decl);\n+  rust_assert (builtin_decl != error_mark_node);\n+\n+  tree builtin_fn = build_fold_addr_expr_loc (locus, builtin_decl);\n+  tree clz_expr\n+    = Backend::call_expression (builtin_fn, {call_arg}, nullptr, locus);\n+\n+  if (diff > 0)\n+    {\n+      tree diff_cst = build_int_cst (integer_type_node, diff);\n+      clz_expr\n+\t= fold_build2 (MINUS_EXPR, integer_type_node, clz_expr, diff_cst);\n+    }\n+\n+  clz_expr = fold_convert (uint32_type_node, clz_expr);\n+\n+  tree final_expr;\n+  if (!nonzero)\n+    {\n+      // ctlz(0) must return bit_size per the Rust reference.\n+      // We cannot pass 0 to __builtin_clz* (UB), so emit:\n+      //   arg == 0 ? bit_size : clz_expr\n+      tree zero = build_int_cst (arg_type, 0);\n+      tree cmp = fold_build2 (EQ_EXPR, boolean_type_node, arg_expr, zero);\n+      tree width_cst = build_int_cst (uint32_type_node, bit_size);\n+      final_expr\n+\t= fold_build3 (COND_EXPR, uint32_type_node, cmp, width_cst, clz_expr);\n+    }\n+  else\n+    {\n+      // ctlz_nonzero: arg != 0 is guaranteed by the caller, no guard needed.\n+      final_expr = clz_expr;\n+    }\n+\n+  tree result = fold_convert (TREE_TYPE (DECL_RESULT (fndecl)), final_expr);\n+  auto return_stmt = Backend::return_statement (fndecl, result, locus);\n+  ctx->add_statement (return_stmt);\n+  // BUILTIN ctlz FN BODY END\n+\n+  finalize_intrinsic_block (ctx, fndecl);\n+  return fndecl;\n+}\n+\n } // namespace inner\n \n const HandlerBuilder\n@@ -1530,6 +1675,18 @@ bswap_handler (Context *ctx, TyTy::FnType *fntype)\n   return fndecl;\n }\n \n+tree\n+ctlz_handler (Context *ctx, TyTy::FnType *fntype)\n+{\n+  return inner::ctlz_handler (ctx, fntype, false);\n+}\n+\n+tree\n+ctlz_nonzero_handler (Context *ctx, TyTy::FnType *fntype)\n+{\n+  return inner::ctlz_handler (ctx, fntype, true);\n+}\n+\n } // namespace handlers\n } // namespace Compile\n } // namespace Rust\ndiff --git a/gcc/rust/backend/rust-intrinsic-handlers.h b/gcc/rust/backend/rust-intrinsic-handlers.h\nindex 06174a53574..52462407f82 100644\n--- a/gcc/rust/backend/rust-intrinsic-handlers.h\n+++ b/gcc/rust/backend/rust-intrinsic-handlers.h\n@@ -65,6 +65,8 @@ tree assume (Context *ctx, TyTy::FnType *fntype);\n tree discriminant_value (Context *ctx, TyTy::FnType *fntype);\n tree variant_count (Context *ctx, TyTy::FnType *fntype);\n tree bswap_handler (Context *ctx, TyTy::FnType *fntype);\n+tree ctlz_handler (Context *ctx, TyTy::FnType *fntype);\n+tree ctlz_nonzero_handler (Context *ctx, TyTy::FnType *fntype);\n \n tree prefetch_data (Context *ctx, TyTy::FnType *fntype, Prefetch kind);\n \ndiff --git a/gcc/rust/util/rust-intrinsic-values.h b/gcc/rust/util/rust-intrinsic-values.h\nindex 6754392a063..1b2d968b908 100644\n--- a/gcc/rust/util/rust-intrinsic-values.h\n+++ b/gcc/rust/util/rust-intrinsic-values.h\n@@ -81,6 +81,7 @@ public:\n   static constexpr auto &CALLER_LOCATION = \"caller_location\";\n   static constexpr auto &CTPOP = \"ctpop\";\n   static constexpr auto &CTLZ = \"ctlz\";\n+  static constexpr auto &CTLZ_NONZERO = \"ctlz_nonzero\";\n   static constexpr auto &CTTZ = \"cttz\";\n   static constexpr auto &BSWAP = \"bswap\";\n   static constexpr auto &BITREVERSE = \"bitreverse\";\ndiff --git a/gcc/testsuite/rust/compile/ctlz.rs b/gcc/testsuite/rust/compile/ctlz.rs\nnew file mode 100644\nindex 00000000000..b886be774ea\n--- /dev/null\n+++ b/gcc/testsuite/rust/compile/ctlz.rs\n@@ -0,0 +1,17 @@\n+// { dg-do compile }\n+#![feature(intrinsics, lang_items, no_core)]\n+#![no_core]\n+\n+#[lang = \"sized\"]\n+pub trait Sized {}\n+\n+#[lang = \"copy\"]\n+pub trait Copy {}\n+\n+extern \"rust-intrinsic\" {\n+    pub fn ctlz<T>(x: T) -> u32; // { dg-error \"ctlz intrinsics can only be used with basic integer types .got 'bool'.\" }\n+}\n+\n+fn main() {\n+    let _ = ctlz(true);\n+}\ndiff --git a/gcc/testsuite/rust/compile/ctlz_nonzero.rs b/gcc/testsuite/rust/compile/ctlz_nonzero.rs\nnew file mode 100644\nindex 00000000000..bf12728d215\n--- /dev/null\n+++ b/gcc/testsuite/rust/compile/ctlz_nonzero.rs\n@@ -0,0 +1,19 @@\n+// { dg-do compile }\n+#![feature(intrinsics, lang_items, no_core)]\n+#![no_core]\n+\n+#[lang = \"sized\"]\n+pub trait Sized {}\n+\n+#[lang = \"copy\"]\n+pub trait Copy {}\n+\n+extern \"rust-intrinsic\" {\n+    pub fn ctlz_nonzero<T>(x: T) -> u32; // { dg-error \"ctlz intrinsics can only be used with basic integer types .got 'bool'.\" }\n+}\n+\n+fn main() {\n+    unsafe {\n+        let _ = ctlz_nonzero(true);\n+    }\n+}\ndiff --git a/gcc/testsuite/rust/execute/torture/ctlz.rs b/gcc/testsuite/rust/execute/torture/ctlz.rs\nnew file mode 100644\nindex 00000000000..bd8afba223f\n--- /dev/null\n+++ b/gcc/testsuite/rust/execute/torture/ctlz.rs\n@@ -0,0 +1,56 @@\n+#![feature(no_core)]\n+#![no_core]\n+#![feature(intrinsics)]\n+#![feature(lang_items)]\n+\n+#[lang = \"sized\"]\n+pub trait Sized {}\n+\n+extern \"rust-intrinsic\" {\n+    pub fn ctlz<T>(x: T) -> u32;\n+    pub fn abort() -> !;\n+}\n+\n+fn main() -> i32 {\n+    if ctlz(0u8) != 8 {\n+        abort();\n+    }\n+    if ctlz(1u8) != 7 {\n+        abort();\n+    }\n+    if ctlz(255u8) != 0 {\n+        abort();\n+    }\n+\n+    if ctlz(0u16) != 16 {\n+        abort();\n+    }\n+    if ctlz(1u16) != 15 {\n+        abort();\n+    }\n+    if ctlz(0xFFFFu16) != 0 {\n+        abort();\n+    }\n+\n+    if ctlz(0u32) != 32 {\n+        abort();\n+    }\n+    if ctlz(1u32) != 31 {\n+        abort();\n+    }\n+    if ctlz(0xFFFFFFFFu32) != 0 {\n+        abort();\n+    }\n+\n+    if ctlz(0u64) != 64 {\n+        abort();\n+    }\n+    if ctlz(1u64) != 63 {\n+        abort();\n+    }\n+    if ctlz(!0u64) != 0 {\n+        abort();\n+    }\n+\n+    0\n+}\ndiff --git a/gcc/testsuite/rust/execute/torture/ctlz_nonzero.rs b/gcc/testsuite/rust/execute/torture/ctlz_nonzero.rs\nnew file mode 100644\nindex 00000000000..3476ab2b9a6\n--- /dev/null\n+++ b/gcc/testsuite/rust/execute/torture/ctlz_nonzero.rs\n@@ -0,0 +1,46 @@\n+#![feature(no_core)]\n+#![no_core]\n+#![feature(intrinsics)]\n+#![feature(lang_items)]\n+\n+#[lang = \"sized\"]\n+pub trait Sized {}\n+\n+extern \"rust-intrinsic\" {\n+    pub fn ctlz_nonzero<T>(x: T) -> u32;\n+    pub fn abort() -> !;\n+}\n+\n+fn main() -> i32 {\n+    unsafe {\n+        if ctlz_nonzero(1u8) != 7 {\n+            abort();\n+        }\n+        if ctlz_nonzero(255u8) != 0 {\n+            abort();\n+        }\n+\n+        if ctlz_nonzero(1u16) != 15 {\n+            abort();\n+        }\n+        if ctlz_nonzero(0xFFFFu16) != 0 {\n+            abort();\n+        }\n+\n+        if ctlz_nonzero(1u32) != 31 {\n+            abort();\n+        }\n+        if ctlz_nonzero(0xFFFFFFFFu32) != 0 {\n+            abort();\n+        }\n+\n+        if ctlz_nonzero(1u64) != 63 {\n+            abort();\n+        }\n+        if ctlz_nonzero(!0u64) != 0 {\n+            abort();\n+        }\n+    }\n+\n+    0\n+}\n",
    "prefixes": [
        "COMMITTED",
        "10/43"
    ]
}