add const_allocate intrisic

Author: vn-ki

compiler/rustc_mir/src/interpret/intern.rs

@@ -104,7 +104,7 @@ fn intern_shallow<'rt, 'mir, 'tcx, M: CompileTimeMachine<'mir, 'tcx>>(
     // This match is just a canary for future changes to `MemoryKind`, which most likely need
     // changes in this function.
     match kind {
-        MemoryKind::Stack | MemoryKind::Vtable | MemoryKind::CallerLocation => {}
+        MemoryKind::Stack | MemoryKind::Heap | MemoryKind::Vtable | MemoryKind::CallerLocation => {}
     }
     // Set allocation mutability as appropriate. This is used by LLVM to put things into
     // read-only memory, and also by Miri when evaluating other globals that

compiler/rustc_mir/src/interpret/intrinsics.rs

@@ -14,10 +14,11 @@ use rustc_middle::ty;
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{Ty, TyCtxt};
 use rustc_span::symbol::{sym, Symbol};
-use rustc_target::abi::{Abi, LayoutOf as _, Primitive, Size};
+use rustc_target::abi::{Abi, Align, LayoutOf as _, Primitive, Size};
 
 use super::{
-    util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, OpTy, PlaceTy,
+    util::ensure_monomorphic_enough, CheckInAllocMsg, ImmTy, InterpCx, Machine, MemoryKind, OpTy,
+    PlaceTy,
 };
 
 mod caller_location;
@@ -337,6 +338,19 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let result = Scalar::from_uint(truncated_bits, layout.size);
                 self.write_scalar(result, dest)?;
             }
+            sym::const_allocate => {
+                let size = self.read_scalar(args[0])?.to_machine_usize(self)?;
+                let align = self.read_scalar(args[1])?.to_machine_usize(self)?;
+
+                let align = match Align::from_bytes(align) {
+                    Ok(a) => a,
+                    Err(err) => bug!("align has to power of 2, {}", err),
+                };
+
+                let ptr =
+                    self.memory.allocate(Size::from_bytes(size as u64), align, MemoryKind::Heap);
+                self.write_scalar(Scalar::Ptr(ptr), dest)?;
+            }
             sym::offset => {
                 let ptr = self.read_scalar(args[0])?.check_init()?;
                 let offset_count = self.read_scalar(args[1])?.to_machine_isize(self)?;

compiler/rustc_mir/src/interpret/memory.rs

@@ -27,6 +27,8 @@ use crate::util::pretty;
 pub enum MemoryKind<T> {
     /// Stack memory. Error if deallocated except during a stack pop.
     Stack,
+    /// Heap memory.
+    Heap,
     /// Memory backing vtables. Error if ever deallocated.
     Vtable,
     /// Memory allocated by `caller_location` intrinsic. Error if ever deallocated.
@@ -40,6 +42,7 @@ impl<T: MayLeak> MayLeak for MemoryKind<T> {
     fn may_leak(self) -> bool {
         match self {
             MemoryKind::Stack => false,
+            MemoryKind::Heap => true,
             MemoryKind::Vtable => true,
             MemoryKind::CallerLocation => true,
             MemoryKind::Machine(k) => k.may_leak(),
@@ -51,6 +54,7 @@ impl<T: fmt::Display> fmt::Display for MemoryKind<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             MemoryKind::Stack => write!(f, "stack variable"),
+            MemoryKind::Heap => write!(f, "heap variable"),
             MemoryKind::Vtable => write!(f, "vtable"),
             MemoryKind::CallerLocation => write!(f, "caller location"),
             MemoryKind::Machine(m) => write!(f, "{}", m),

compiler/rustc_span/src/symbol.rs

@@ -356,6 +356,7 @@ symbols! {
         concat_idents,
         conservative_impl_trait,
         console,
+        const_allocate,
         const_compare_raw_pointers,
         const_constructor,
         const_eval_limit,

compiler/rustc_typeck/src/check/intrinsic.rs

@@ -286,6 +286,10 @@ pub fn check_intrinsic_type(tcx: TyCtxt<'_>, it: &hir::ForeignItem<'_>) {
                 (1, vec![tcx.mk_imm_ptr(param(0)), tcx.mk_imm_ptr(param(0))], tcx.types.bool)
             }
 
+            sym::const_allocate => {
+                (0, vec![tcx.types.usize, tcx.types.usize], tcx.mk_mut_ptr(tcx.types.u8))
+            }
+
             sym::ptr_offset_from => {
                 (1, vec![tcx.mk_imm_ptr(param(0)), tcx.mk_imm_ptr(param(0))], tcx.types.isize)
             }

library/core/src/intrinsics.rs

@@ -1732,6 +1732,11 @@ extern "rust-intrinsic" {
     /// See documentation of `<*const T>::guaranteed_ne` for details.
     #[rustc_const_unstable(feature = "const_raw_ptr_comparison", issue = "53020")]
     pub fn ptr_guaranteed_ne<T>(ptr: *const T, other: *const T) -> bool;
+
+    /// Allocate at compile time. Should not be called at runtime.
+    #[rustc_const_unstable(feature = "const_heap", issue = "none")]
+    #[cfg(not(bootstrap))]
+    pub fn const_allocate(size: usize, align: usize) -> *mut u8;
 }
 
 // Some functions are defined here because they accidentally got made

library/core/src/lib.rs

@@ -68,6 +68,7 @@
 #![feature(arbitrary_self_types)]
 #![feature(asm)]
 #![feature(cfg_target_has_atomic)]
+#![cfg_attr(not(bootstrap), feature(const_heap))]
 #![feature(const_alloc_layout)]
 #![feature(const_discriminant)]
 #![feature(const_cell_into_inner)]

src/test/ui/consts/const-eval/heap/alloc_intrinsic_nontransient.rs

@@ -0,0 +1,20 @@
+// run-pass
+#![feature(core_intrinsics)]
+#![feature(const_heap)]
+#![feature(const_raw_ptr_deref)]
+#![feature(const_mut_refs)]
+use std::intrinsics;
+
+const FOO: *const i32 = foo();
+
+const fn foo() -> &'static i32 {
+    let t = unsafe {
+        let i = intrinsics::const_allocate(4, 4) as * mut i32;
+        *i = 20;
+        i
+    };
+    unsafe { &*t }
+}
+fn main() {
+    assert_eq!(unsafe { *FOO }, 20)
+}

src/test/ui/consts/const-eval/heap/alloc_intrinsic_transient.rs

@@ -0,0 +1,20 @@
+// run-pass
+#![feature(core_intrinsics)]
+#![feature(const_heap)]
+#![feature(const_raw_ptr_deref)]
+#![feature(const_mut_refs)]
+use std::intrinsics;
+
+const FOO: i32 = foo();
+
+const fn foo() -> i32 {
+    let t = unsafe {
+        let i = intrinsics::const_allocate(4, 4) as * mut i32;
+        *i = 20;
+        i
+    };
+    unsafe { *t }
+}
+fn main() {
+    assert_eq!(FOO, 20);
+}

src/test/ui/consts/const-eval/heap/alloc_intrinsic_uninit.rs

@@ -0,0 +1,10 @@
+// compile-test
+#![feature(core_intrinsics)]
+#![feature(const_heap)]
+#![feature(const_raw_ptr_deref)]
+#![feature(const_mut_refs)]
+use std::intrinsics;
+
+const BAR: &i32 = unsafe { &*(intrinsics::const_allocate(4, 4) as *mut i32) };
+//~^ error: it is undefined behavior to use this value
+fn main() {}