Introduce const_cstr!() macro and use it where applicable.

Author: michaelwoerister

src/librustc_codegen_llvm/attributes.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 //! Set and unset common attributes on LLVM values.
 
-use std::ffi::{CStr, CString};
+use std::ffi::CString;
 
 use rustc::hir::CodegenFnAttrFlags;
 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
@@ -75,7 +75,7 @@ pub fn set_frame_pointer_elimination(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value)
     if cx.sess().must_not_eliminate_frame_pointers() {
         llvm::AddFunctionAttrStringValue(
             llfn, llvm::AttributePlace::Function,
-            cstr("no-frame-pointer-elim\0"), cstr("true\0"));
+            const_cstr!("no-frame-pointer-elim"), const_cstr!("true"));
     }
 }
 
@@ -108,7 +108,7 @@ pub fn set_probestack(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
     // This is defined in the `compiler-builtins` crate for each architecture.
     llvm::AddFunctionAttrStringValue(
         llfn, llvm::AttributePlace::Function,
-        cstr("probe-stack\0"), cstr("__rust_probestack\0"));
+        const_cstr!("probe-stack"), const_cstr!("__rust_probestack"));
 }
 
 pub fn llvm_target_features(sess: &Session) -> impl Iterator<Item = &str> {
@@ -202,7 +202,7 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value, id: DefId) {
         let val = CString::new(features).unwrap();
         llvm::AddFunctionAttrStringValue(
             llfn, llvm::AttributePlace::Function,
-            cstr("target-features\0"), &val);
+            const_cstr!("target-features"), &val);
     }
 
     // Note that currently the `wasm-import-module` doesn't do anything, but
@@ -213,17 +213,13 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value, id: DefId) {
             llvm::AddFunctionAttrStringValue(
                 llfn,
                 llvm::AttributePlace::Function,
-                cstr("wasm-import-module\0"),
+                const_cstr!("wasm-import-module"),
                 &module,
             );
         }
     }
 }
 
-fn cstr(s: &'static str) -> &CStr {
-    CStr::from_bytes_with_nul(s.as_bytes()).expect("null-terminated string")
-}
-
 pub fn provide(providers: &mut Providers) {
     providers.target_features_whitelist = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);

src/librustc_codegen_llvm/base.rs

@@ -1255,8 +1255,8 @@ fn compile_codegen_unit<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             // Create the llvm.used variable
             // This variable has type [N x i8*] and is stored in the llvm.metadata section
             if !cx.used_statics.borrow().is_empty() {
-                let name = CString::new("llvm.used").unwrap();
-                let section = CString::new("llvm.metadata").unwrap();
+                let name = const_cstr!("llvm.used");
+                let section = const_cstr!("llvm.metadata");
                 let array = C_array(Type::i8(&cx).ptr_to(), &*cx.used_statics.borrow());
 
                 unsafe {

src/librustc_codegen_llvm/builder.rs

@@ -975,7 +975,7 @@ impl Builder<'a, 'll, 'tcx> {
                        parent: Option<&'ll Value>,
                        args: &[&'ll Value]) -> &'ll Value {
         self.count_insn("cleanuppad");
-        let name = CString::new("cleanuppad").unwrap();
+        let name = const_cstr!("cleanuppad");
         let ret = unsafe {
             llvm::LLVMRustBuildCleanupPad(self.llbuilder,
                                           parent,
@@ -1001,7 +1001,7 @@ impl Builder<'a, 'll, 'tcx> {
                      parent: &'ll Value,
                      args: &[&'ll Value]) -> &'ll Value {
         self.count_insn("catchpad");
-        let name = CString::new("catchpad").unwrap();
+        let name = const_cstr!("catchpad");
         let ret = unsafe {
             llvm::LLVMRustBuildCatchPad(self.llbuilder, parent,
                                         args.len() as c_uint, args.as_ptr(),
@@ -1025,7 +1025,7 @@ impl Builder<'a, 'll, 'tcx> {
         num_handlers: usize,
     ) -> &'ll Value {
         self.count_insn("catchswitch");
-        let name = CString::new("catchswitch").unwrap();
+        let name = const_cstr!("catchswitch");
         let ret = unsafe {
             llvm::LLVMRustBuildCatchSwitch(self.llbuilder, parent, unwind,
                                            num_handlers as c_uint,

src/librustc_codegen_llvm/consts.rs

@@ -328,7 +328,7 @@ pub fn codegen_static<'a, 'tcx>(
         } else {
             // If we created the global with the wrong type,
             // correct the type.
-            let empty_string = CString::new("").unwrap();
+            let empty_string = const_cstr!("");
             let name_str_ref = CStr::from_ptr(llvm::LLVMGetValueName(g));
             let name_string = CString::new(name_str_ref.to_bytes()).unwrap();
             llvm::LLVMSetValueName(g, empty_string.as_ptr());

src/librustc_codegen_llvm/debuginfo/metadata.rs

@@ -883,7 +883,7 @@ pub fn compile_unit_metadata(tcx: TyCtxt,
                                                           gcov_cu_info.as_ptr(),
                                                           gcov_cu_info.len() as c_uint);
 
-            let llvm_gcov_ident = CString::new("llvm.gcov").unwrap();
+            let llvm_gcov_ident = const_cstr!("llvm.gcov");
             llvm::LLVMAddNamedMetadataOperand(debug_context.llmod,
                                               llvm_gcov_ident.as_ptr(),
                                               gcov_metadata);
@@ -1780,7 +1780,7 @@ pub fn create_vtable_metadata(
         // later on in llvm/lib/IR/Value.cpp.
         let empty_array = create_DIArray(DIB(cx), &[]);
 
-        let name = CString::new("vtable").unwrap();
+        let name = const_cstr!("vtable");
 
         // Create a new one each time.  We don't want metadata caching
         // here, because each vtable will refer to a unique containing

src/librustc_data_structures/const_cstr.rs

@@ -0,0 +1,42 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+/// This macro creates a zero-overhead &CStr by adding a NUL terminator to
+/// the string literal passed into it at compile-time. Use it like:
+///
+/// ```
+///     let some_const_cstr = const_cstr!("abc");
+/// ```
+///
+/// The above is roughly equivalent to:
+///
+/// ```
+///     let some_const_cstr = CStr::from_bytes_with_nul(b"abc\0").unwrap()
+/// ```
+///
+/// Note that macro only checks the string literal for internal NULs if
+/// debug-assertions are enabled in order to avoid runtime overhead in release
+/// builds.
+#[macro_export]
+macro_rules! const_cstr {
+    ($s:expr) => ({
+        use std::ffi::CStr;
+
+        let str_plus_nul = concat!($s, "\0");
+
+        if cfg!(debug_assertions) {
+            CStr::from_bytes_with_nul(str_plus_nul.as_bytes()).unwrap()
+        } else {
+            unsafe {
+                CStr::from_bytes_with_nul_unchecked(str_plus_nul.as_bytes())
+            }
+        }
+    })
+}

src/librustc_data_structures/lib.rs

@@ -60,6 +60,7 @@ pub mod array_vec;
 pub mod base_n;
 pub mod bitslice;
 pub mod bitvec;
+pub mod const_cstr;
 pub mod flock;
 pub mod fx;
 pub mod graph;