Organize intrinsics promotion checks

Author: vertexclique

src/libcore/intrinsics.rs

@@ -913,6 +913,7 @@ extern "rust-intrinsic" {
  /// }
  /// ```
  #[stable(feature = "rust1", since = "1.0.0")]
+ #[rustc_const_unstable(feature = "const_transmute")]
  pub fn transmute<T, U>(e: T) -> U;
 
  /// Returns `true` if the actual type given as `T` requires drop

src/librustc/ty/constness.rs

@@ -2,7 +2,12 @@ use crate::ty::query::Providers;
 use crate::hir::def_id::DefId;
 use crate::hir;
 use crate::ty::TyCtxt;
+<<<<<<< HEAD
 use syntax_pos::symbol::{sym, Symbol};
+=======
+use syntax_pos::symbol::Symbol;
+use rustc_target::spec::abi::Abi;
+>>>>>>> Organize intrinsics promotion checks
 use crate::hir::map::blocks::FnLikeNode;
 use syntax::attr;
 
@@ -68,16 +73,52 @@ impl<'tcx> TyCtxt<'tcx, 'tcx> {
 
 
 pub fn provide<'tcx>(providers: &mut Providers<'tcx>) {
- /// only checks whether the function has a `const` modifier
- fn is_const_fn_raw<'tcx>(tcx: TyCtxt<'tcx, 'tcx>, def_id: DefId) -> bool {
+ fn is_intrinsic_promotable(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
+ // Intrinsics promotion whitelist is here to check const context at the top level beforehand.
+ match tcx.fn_sig(def_id).abi() {
+ Abi::RustIntrinsic |
+ Abi::PlatformIntrinsic => {
+ match &tcx.item_name(def_id).as_str()[..] {
+ | "size_of"
+ | "min_align_of"
+ | "needs_drop"
+ | "type_id"
+ | "bswap"
+ | "bitreverse"
+ | "ctpop"
+ | "cttz"
+ | "cttz_nonzero"
+ | "ctlz"
+ | "ctlz_nonzero"
+ | "overflowing_add"
+ | "overflowing_sub"
+ | "overflowing_mul"
+ | "unchecked_shl"
+ | "unchecked_shr"
+ | "rotate_left"
+ | "rotate_right"
+ | "add_with_overflow"
+ | "sub_with_overflow"
+ | "mul_with_overflow"
+ | "saturating_add"
+ | "saturating_sub"
+ | "transmute"
+ => true,
+
+ _ => false
+ }
+ }
+ _ => false
+ }
+ }
+
+ /// Checks whether the function has a `const` modifier and intrinsics can be promotable in it
+ fn is_const_fn_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
  let hir_id = tcx.hir().as_local_hir_id(def_id)
  .expect("Non-local call to local provider is_const_fn");
 
- let node = tcx.hir().get_by_hir_id(hir_id);
- if let Some(fn_like) = FnLikeNode::from_node(node) {
- fn_like.constness() == hir::Constness::Const
- } else if let hir::Node::Ctor(_) = node {
- true
+ if let Some(fn_like) = FnLikeNode::from_node(tcx.hir().get_by_hir_id(hir_id)) {
+ (fn_like.constness() == hir::Constness::Const) || is_intrinsic_promotable(tcx, def_id)
  } else {
  false
  }

src/librustc_mir/transform/qualify_consts.rs

@@ -489,49 +489,12 @@ impl Qualif for IsNotPromotable {
  let fn_ty = callee.ty(cx.body, cx.tcx);
  match fn_ty.sty {
  ty::FnDef(def_id, _) => {
- match cx.tcx.fn_sig(def_id).abi() {
- Abi::RustIntrinsic |
- Abi::PlatformIntrinsic => {
- assert!(!cx.tcx.is_const_fn(def_id));
- match &cx.tcx.item_name(def_id).as_str()[..] {
- | "size_of"
- | "min_align_of"
- | "needs_drop"
- | "type_id"
- | "bswap"
- | "bitreverse"
- | "ctpop"
- | "cttz"
- | "cttz_nonzero"
- | "ctlz"
- | "ctlz_nonzero"
- | "overflowing_add"
- | "overflowing_sub"
- | "overflowing_mul"
- | "unchecked_shl"
- | "unchecked_shr"
- | "rotate_left"
- | "rotate_right"
- | "add_with_overflow"
- | "sub_with_overflow"
- | "mul_with_overflow"
- | "saturating_add"
- | "saturating_sub"
- | "transmute"
- => return true,
-
- _ => {}
- }
- }
- _ => {
- let is_const_fn =
- cx.tcx.is_const_fn(def_id) ||
- cx.tcx.is_unstable_const_fn(def_id).is_some() ||
- cx.is_const_panic_fn(def_id);
- if !is_const_fn {
- return true;
- }
- }
+ let is_const_fn =
+ cx.tcx.is_const_fn(def_id) ||
+ cx.tcx.is_unstable_const_fn(def_id).is_some() ||
+ cx.is_const_panic_fn(def_id);
+ if !is_const_fn {
+ return true;
  }
  }
  _ => return true,
@@ -1251,21 +1214,6 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
  Abi::PlatformIntrinsic => {
  assert!(!self.tcx.is_const_fn(def_id));
  match &self.tcx.item_name(def_id).as_str()[..] {
- // special intrinsic that can be called diretly without an intrinsic
- // feature gate needs a language feature gate
- "transmute" => {
- if self.mode.requires_const_checking() {
- // const eval transmute calls only with the feature gate
- if !self.tcx.features().const_transmute {
- emit_feature_err(
- &self.tcx.sess.parse_sess, sym::const_transmute,
- self.span, GateIssue::Language,
- &format!("The use of std::mem::transmute() \
- is gated in {}s", self.mode));
- }
- }
- }
-
  name if name.starts_with("simd_shuffle") => {
  is_shuffle = true;
  }
@@ -1276,8 +1224,8 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
  }
  }
  _ => {
- // In normal functions no calls are feature-gated.
- if self.mode.requires_const_checking() {
+ // Apply normal functions' rules which are not feature-gated.
+ if self.mode != Mode::Fn {
  let unleash_miri = self
  .tcx
  .sess

src/libsyntax/feature_gate.rs

@@ -489,9 +489,6 @@ declare_features! (
  // This will likely be removed prior to stabilization of async/await.
  (active, await_macro, "1.28.0", Some(50547), None),
 
- // Allows reinterpretation of the bits of a value of one type as another type during const eval.
- (active, const_transmute, "1.29.0", Some(53605), None),
-
  // Allows using `try {...}` expressions.
  (active, try_blocks, "1.29.0", Some(31436), None),