miri: optimize zeroed alloc

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -420,6 +420,7 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
                     Size::from_bytes(size),
                     align,
                     interpret::MemoryKind::Machine(MemoryKind::Heap),
+                    false,
                 )?;
                 ecx.write_pointer(ptr, dest)?;
             }

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -230,11 +230,12 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         size: Size,
         align: Align,
         kind: MemoryKind<M::MemoryKind>,
+        zero_init: bool,
     ) -> InterpResult<'tcx, Pointer<M::Provenance>> {
         let alloc = if M::PANIC_ON_ALLOC_FAIL {
-            Allocation::uninit(size, align)
+            Allocation::new(size, align, zero_init)
         } else {
-            Allocation::try_uninit(size, align)?
+            Allocation::try_new(size, align, zero_init)?
         };
         self.insert_allocation(alloc, kind)
     }
@@ -277,6 +278,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         new_size: Size,
         new_align: Align,
         kind: MemoryKind<M::MemoryKind>,
+        zero_init: bool,
     ) -> InterpResult<'tcx, Pointer<M::Provenance>> {
         let (alloc_id, offset, _prov) = self.ptr_get_alloc_id(ptr, 0)?;
         if offset.bytes() != 0 {
@@ -289,7 +291,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
         // For simplicities' sake, we implement reallocate as "alloc, copy, dealloc".
         // This happens so rarely, the perf advantage is outweighed by the maintenance cost.
-        let new_ptr = self.allocate_ptr(new_size, new_align, kind)?;
+        let new_ptr = self.allocate_ptr(new_size, new_align, kind, zero_init)?;
         let old_size = match old_size_and_align {
             Some((size, _align)) => size,
             None => self.get_alloc_raw(alloc_id)?.size(),

compiler/rustc_const_eval/src/interpret/place.rs

@@ -983,7 +983,7 @@ where
         let Some((size, align)) = self.size_and_align_of(&meta, &layout)? else {
             span_bug!(self.cur_span(), "cannot allocate space for `extern` type, size is not known")
         };
-        let ptr = self.allocate_ptr(size, align, kind)?;
+        let ptr = self.allocate_ptr(size, align, kind, false)?;
         interp_ok(self.ptr_with_meta_to_mplace(ptr.into(), meta, layout, /*unaligned*/ false))
     }
 

compiler/rustc_const_eval/src/interpret/util.rs

@@ -76,7 +76,7 @@ pub(crate) fn create_static_alloc<'tcx>(
     static_def_id: LocalDefId,
     layout: TyAndLayout<'tcx>,
 ) -> InterpResult<'tcx, MPlaceTy<'tcx>> {
-    let alloc = Allocation::try_uninit(layout.size, layout.align.abi)?;
+    let alloc = Allocation::try_new(layout.size, layout.align.abi, false)?;
     let alloc_id = ecx.tcx.reserve_and_set_static_alloc(static_def_id.into());
     assert_eq!(ecx.machine.static_root_ids, None);
     ecx.machine.static_root_ids = Some((alloc_id, static_def_id));

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -294,7 +294,12 @@ impl<Prov: Provenance, Bytes: AllocBytes> Allocation<Prov, (), Bytes> {
         Allocation::from_bytes(slice, Align::ONE, Mutability::Not)
     }
 
-    fn uninit_inner<R>(size: Size, align: Align, fail: impl FnOnce() -> R) -> Result<Self, R> {
+    fn new_inner<R>(
+        size: Size,
+        align: Align,
+        zero_init: bool,
+        fail: impl FnOnce() -> R,
+    ) -> Result<Self, R> {
         // We raise an error if we cannot create the allocation on the host.
         // This results in an error that can happen non-deterministically, since the memory
         // available to the compiler can change between runs. Normally queries are always
@@ -306,7 +311,7 @@ impl<Prov: Provenance, Bytes: AllocBytes> Allocation<Prov, (), Bytes> {
         Ok(Allocation {
             bytes,
             provenance: ProvenanceMap::new(),
-            init_mask: InitMask::new(size, false),
+            init_mask: InitMask::new(size, zero_init),
             align,
             mutability: Mutability::Mut,
             extra: (),
@@ -315,8 +320,8 @@ impl<Prov: Provenance, Bytes: AllocBytes> Allocation<Prov, (), Bytes> {
 
     /// Try to create an Allocation of `size` bytes, failing if there is not enough memory
     /// available to the compiler to do so.
-    pub fn try_uninit<'tcx>(size: Size, align: Align) -> InterpResult<'tcx, Self> {
-        Self::uninit_inner(size, align, || {
+    pub fn try_new<'tcx>(size: Size, align: Align, zero_init: bool) -> InterpResult<'tcx, Self> {
+        Self::new_inner(size, align, zero_init, || {
             ty::tls::with(|tcx| tcx.dcx().delayed_bug("exhausted memory during interpretation"));
             InterpErrorKind::ResourceExhaustion(ResourceExhaustionInfo::MemoryExhausted)
         })
@@ -328,8 +333,8 @@ impl<Prov: Provenance, Bytes: AllocBytes> Allocation<Prov, (), Bytes> {
     ///
     /// Example use case: To obtain an Allocation filled with specific data,
     /// first call this function and then call write_scalar to fill in the right data.
-    pub fn uninit(size: Size, align: Align) -> Self {
-        match Self::uninit_inner(size, align, || {
+    pub fn new(size: Size, align: Align, zero_init: bool) -> Self {
+        match Self::new_inner(size, align, zero_init, || {
             panic!(
                 "interpreter ran out of memory: cannot create allocation of {} bytes",
                 size.bytes()

compiler/rustc_middle/src/ty/vtable.rs

@@ -108,7 +108,7 @@ pub(super) fn vtable_allocation_provider<'tcx>(
     let ptr_align = tcx.data_layout.pointer_align.abi;
 
     let vtable_size = ptr_size * u64::try_from(vtable_entries.len()).unwrap();
-    let mut vtable = Allocation::uninit(vtable_size, ptr_align);
+    let mut vtable = Allocation::new(vtable_size, ptr_align, false);
 
     // No need to do any alignment checks on the memory accesses below, because we know the
     // allocation is correctly aligned as we created it above. Also we're only offsetting by

compiler/rustc_smir/src/rustc_smir/alloc.rs

@@ -44,7 +44,8 @@ pub(crate) fn try_new_allocation<'tcx>(
                 .layout_of(rustc_middle::ty::TypingEnv::fully_monomorphized().as_query_input(ty))
                 .map_err(|e| e.stable(tables))?
                 .align;
-            let mut allocation = rustc_middle::mir::interpret::Allocation::uninit(size, align.abi);
+            let mut allocation =
+                rustc_middle::mir::interpret::Allocation::new(size, align.abi, false);
             allocation
                 .write_scalar(&tables.tcx, alloc_range(Size::ZERO, size), scalar)
                 .map_err(|e| e.stable(tables))?;
@@ -69,7 +70,7 @@ pub(crate) fn try_new_allocation<'tcx>(
                 .layout_of(rustc_middle::ty::TypingEnv::fully_monomorphized().as_query_input(ty))
                 .map_err(|e| e.stable(tables))?;
             let mut allocation =
-                rustc_middle::mir::interpret::Allocation::uninit(layout.size, layout.align.abi);
+                rustc_middle::mir::interpret::Allocation::new(layout.size, layout.align.abi, false);
             allocation
                 .write_scalar(
                     &tables.tcx,

src/tools/miri/src/shims/alloc.rs

@@ -1,5 +1,3 @@
-use std::iter;
-
 use rustc_abi::{Align, Size};
 use rustc_ast::expand::allocator::AllocatorKind;
 
@@ -83,15 +81,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
     fn malloc(&mut self, size: u64, zero_init: bool) -> InterpResult<'tcx, Pointer> {
         let this = self.eval_context_mut();
         let align = this.malloc_align(size);
-        let ptr = this.allocate_ptr(Size::from_bytes(size), align, MiriMemoryKind::C.into())?;
-        if zero_init {
-            // We just allocated this, the access is definitely in-bounds and fits into our address space.
-            this.write_bytes_ptr(
-                ptr.into(),
-                iter::repeat(0u8).take(usize::try_from(size).unwrap()),
-            )
-            .unwrap();
-        }
+        let ptr = this.allocate_ptr(Size::from_bytes(size), align, MiriMemoryKind::C.into(), zero_init)?;
         interp_ok(ptr.into())
     }
 
@@ -115,6 +105,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 Size::from_bytes(size),
                 Align::from_bytes(align).unwrap(),
                 MiriMemoryKind::C.into(),
+                false
             )?;
             this.write_pointer(ptr, &memptr)?;
             interp_ok(Scalar::from_i32(0))
@@ -147,6 +138,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     Size::from_bytes(new_size),
                     new_align,
                     MiriMemoryKind::C.into(),
+                    false
                 )?;
                 interp_ok(new_ptr.into())
             }
@@ -187,6 +179,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     Size::from_bytes(size),
                     Align::from_bytes(align).unwrap(),
                     MiriMemoryKind::C.into(),
+                    false
                 )?;
                 interp_ok(ptr.into())
             }

src/tools/miri/src/shims/foreign_items.rs

@@ -1,6 +1,5 @@
 use std::collections::hash_map::Entry;
 use std::io::Write;
-use std::iter;
 use std::path::Path;
 
 use rustc_abi::{Align, AlignFromBytesError, Size};
@@ -509,6 +508,7 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                         Size::from_bytes(size),
                         Align::from_bytes(align).unwrap(),
                         memory_kind.into(),
+                        false
                     )?;
 
                     ecx.write_pointer(ptr, dest)
@@ -537,14 +537,8 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                         Size::from_bytes(size),
                         Align::from_bytes(align).unwrap(),
                         MiriMemoryKind::Rust.into(),
+                        true
                     )?;
-
-                    // We just allocated this, the access is definitely in-bounds.
-                    this.write_bytes_ptr(
-                        ptr.into(),
-                        iter::repeat(0u8).take(usize::try_from(size).unwrap()),
-                    )
-                    .unwrap();
                     this.write_pointer(ptr, dest)
                 });
             }
@@ -604,6 +598,7 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                         Size::from_bytes(new_size),
                         align,
                         MiriMemoryKind::Rust.into(),
+                        false
                     )?;
                     this.write_pointer(new_ptr, dest)
                 });

src/tools/miri/src/shims/unix/fs.rs

@@ -1109,6 +1109,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     Size::from_bytes(size),
                     dirent_layout.align.abi,
                     MiriMemoryKind::Runtime.into(),
+                    false
                 )?;
                 let entry: Pointer = entry.into();
 

src/tools/miri/src/shims/unix/linux/mem.rs

@@ -49,16 +49,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             Size::from_bytes(new_size),
             align,
             MiriMemoryKind::Mmap.into(),
+            true
         )?;
-        if let Some(increase) = new_size.checked_sub(old_size) {
-            // We just allocated this, the access is definitely in-bounds and fits into our address space.
-            // mmap guarantees new mappings are zero-init.
-            this.write_bytes_ptr(
-                ptr.wrapping_offset(Size::from_bytes(old_size), this).into(),
-                std::iter::repeat(0u8).take(usize::try_from(increase).unwrap()),
-            )
-            .unwrap();
-        }
 
         interp_ok(Scalar::from_pointer(ptr, this))
     }

src/tools/miri/src/shims/unix/mem.rs

@@ -111,15 +111,13 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             return interp_ok(this.eval_libc("MAP_FAILED"));
         }
 
-        let ptr =
-            this.allocate_ptr(Size::from_bytes(map_length), align, MiriMemoryKind::Mmap.into())?;
-        // We just allocated this, the access is definitely in-bounds and fits into our address space.
-        // mmap guarantees new mappings are zero-init.
-        this.write_bytes_ptr(
-            ptr.into(),
-            std::iter::repeat(0u8).take(usize::try_from(map_length).unwrap()),
-        )
-        .unwrap();
+        let ptr = this.allocate_ptr(
+            Size::from_bytes(map_length),
+            align,
+            MiriMemoryKind::Mmap.into(),
+            // mmap guarantees new mappings are zero-init.
+            true
+        )?;
 
         interp_ok(Scalar::from_pointer(ptr, this))
     }

src/tools/miri/src/shims/windows/foreign_items.rs

@@ -262,13 +262,8 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     Size::from_bytes(size),
                     Align::from_bytes(align).unwrap(),
                     MiriMemoryKind::WinHeap.into(),
+                    zero_init
                 )?;
-                if zero_init {
-                    this.write_bytes_ptr(
-                        ptr.into(),
-                        iter::repeat(0u8).take(usize::try_from(size).unwrap()),
-                    )?;
-                }
                 this.write_pointer(ptr, dest)?;
             }
             "HeapFree" => {
@@ -300,6 +295,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                     Size::from_bytes(size),
                     Align::from_bytes(align).unwrap(),
                     MiriMemoryKind::WinHeap.into(),
+                    false
                 )?;
                 this.write_pointer(new_ptr, dest)?;
             }