rustup: more flexible write_bytes avoids allocations and removes itertools dependency

Author: RalfJung

Cargo.lock

@@ -40,7 +40,6 @@ log = "0.4"
 shell-escape = "0.1.4"
 hex = "0.3.2"
 rand = "0.7"
-itertools = "0.8"
 
 # A noop dependency that changes in the Rust repository, it's a bit of a hack.
 # See the `src/tools/rustc-workspace-hack/README.md` file in `rust-lang/rust`

Cargo.toml

@@ -1 +1 @@
-f466f52c1bf8f2e4454e31c683a88625ad4b4033
+55e00631e5bc5b16d40232914e57deeea197a8e4

rust-version

@@ -1,4 +1,4 @@
-use std::mem;
+use std::{mem, iter};
 use std::ffi::{OsStr, OsString};
 
 use rustc::hir::def_id::{DefId, CRATE_DEF_INDEX};
@@ -428,7 +428,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             return Ok(false);
         }
         // FIXME: We should use `Iterator::chain` instead when rust-lang/rust#65704 lands.
-        self.eval_context_mut().memory.write_bytes(scalar, [bytes, &[0]].concat())?;
+        self.eval_context_mut().memory.write_bytes(scalar, bytes.iter().copied().chain(iter::once(0u8)))?;
         Ok(true)
     }
 }

src/helpers.rs

@@ -1,4 +1,4 @@
-use std::convert::TryInto;
+use std::{iter, convert::TryInto};
 
 use rustc::hir::def_id::DefId;
 use rustc::mir;
@@ -52,7 +52,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
             if zero_init {
                 // We just allocated this, the access is definitely in-bounds.
                 this.memory
-                    .write_bytes(ptr.into(), itertools::repeat_n(0u8, size as usize))
+                    .write_bytes(ptr.into(), iter::repeat(0u8).take(size as usize))
                     .unwrap();
             }
             Scalar::Ptr(ptr)
@@ -227,7 +227,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 );
                 // We just allocated this, the access is definitely in-bounds.
                 this.memory
-                    .write_bytes(ptr.into(), itertools::repeat_n(0u8, size as usize))
+                    .write_bytes(ptr.into(), iter::repeat(0u8).take(size as usize))
                     .unwrap();
                 this.write_scalar(Scalar::Ptr(ptr), dest)?;
             }
@@ -839,7 +839,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let system_info = this.deref_operand(args[0])?;
                 // Initialize with `0`.
                 this.memory
-                    .write_bytes(system_info.ptr, itertools::repeat_n(0, system_info.layout.size.bytes() as usize))?;
+                    .write_bytes(system_info.ptr, iter::repeat(0u8).take(system_info.layout.size.bytes() as usize))?;
                 // Set number of processors.
                 let dword_size = Size::from_bytes(4);
                 let num_cpus = this.mplace_field(system_info, 6)?;

src/shims/foreign_items.rs

@@ -1,3 +1,5 @@
+use std::iter;
+
 use rustc_apfloat::Float;
 use rustc::mir;
 use rustc::mir::interpret::{InterpResult, PointerArithmetic};
@@ -357,7 +359,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                             // Do it in memory
                             let mplace = this.force_allocation(dest)?;
                             mplace.meta.unwrap_none(); // must be sized
-                            this.memory.write_bytes(mplace.ptr, itertools::repeat_n(0, dest.layout.size.bytes() as usize))?;
+                            this.memory.write_bytes(mplace.ptr, iter::repeat(0u8).take(dest.layout.size.bytes() as usize))?;
                         }
                     }
                 }
@@ -562,7 +564,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let ptr = this.read_scalar(args[0])?.not_undef()?;
                 let count = this.read_scalar(args[2])?.to_usize(this)?;
                 let byte_count = ty_layout.size * count;
-                this.memory.write_bytes(ptr, itertools::repeat_n(val_byte, byte_count.bytes() as usize))?;
+                this.memory.write_bytes(ptr, iter::repeat(val_byte).take(byte_count.bytes() as usize))?;
             }
 
             name => throw_unsup_format!("unimplemented intrinsic: {}", name),