Auto merge of #53161 - michaelwoerister:cstrings, r=wesleywiser

Avoid many allocations for CStrings during codegen.

Giving in to my irrational fear of dynamic allocations. Let's see what perf says to this.

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> {
@@ -128,7 +128,7 @@ pub fn apply_target_cpu_attr(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
     llvm::AddFunctionAttrStringValue(
             llfn,
             llvm::AttributePlace::Function,
-            cstr("target-cpu\0"),
+            const_cstr!("target-cpu"),
             target_cpu.as_c_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/back/write.rs

@@ -31,6 +31,7 @@ use rustc::hir::def_id::{CrateNum, LOCAL_CRATE};
 use rustc::ty::TyCtxt;
 use rustc::util::common::{time_ext, time_depth, set_time_depth, print_time_passes_entry};
 use rustc_fs_util::{path2cstr, link_or_copy};
+use rustc_data_structures::small_c_str::SmallCStr;
 use errors::{self, Handler, Level, DiagnosticBuilder, FatalError, DiagnosticId};
 use errors::emitter::{Emitter};
 use syntax::attr;
@@ -170,11 +171,8 @@ pub fn target_machine_factory(sess: &Session, find_features: bool)
 
     let singlethread = sess.target.target.options.singlethread;
 
-    let triple = &sess.target.target.llvm_target;
-
-    let triple = CString::new(triple.as_bytes()).unwrap();
-    let cpu = sess.target_cpu();
-    let cpu = CString::new(cpu.as_bytes()).unwrap();
+    let triple = SmallCStr::new(&sess.target.target.llvm_target);
+    let cpu = SmallCStr::new(sess.target_cpu());
     let features = attributes::llvm_target_features(sess)
         .collect::<Vec<_>>()
         .join(",");
@@ -522,7 +520,7 @@ unsafe fn optimize(cgcx: &CodegenContext,
             // If we're verifying or linting, add them to the function pass
             // manager.
             let addpass = |pass_name: &str| {
-                let pass_name = CString::new(pass_name).unwrap();
+                let pass_name = SmallCStr::new(pass_name);
                 let pass = match llvm::LLVMRustFindAndCreatePass(pass_name.as_ptr()) {
                     Some(pass) => pass,
                     None => return false,

src/librustc_codegen_llvm/base.rs

@@ -73,6 +73,7 @@ use type_::Type;
 use type_of::LayoutLlvmExt;
 use rustc::util::nodemap::{FxHashMap, FxHashSet, DefIdSet};
 use CrateInfo;
+use rustc_data_structures::small_c_str::SmallCStr;
 use rustc_data_structures::sync::Lrc;
 
 use std::any::Any;
@@ -533,7 +534,7 @@ pub fn set_link_section(llval: &Value, attrs: &CodegenFnAttrs) {
         None => return,
     };
     unsafe {
-        let buf = CString::new(sect.as_str().as_bytes()).unwrap();
+        let buf = SmallCStr::new(&sect.as_str());
         llvm::LLVMSetSection(llval, buf.as_ptr());
     }
 }
@@ -681,7 +682,7 @@ fn write_metadata<'a, 'gcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>,
     unsafe {
         llvm::LLVMSetInitializer(llglobal, llconst);
         let section_name = metadata::metadata_section_name(&tcx.sess.target.target);
-        let name = CString::new(section_name).unwrap();
+        let name = SmallCStr::new(section_name);
         llvm::LLVMSetSection(llglobal, name.as_ptr());
 
         // Also generate a .section directive to force no
@@ -1255,8 +1256,8 @@ 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

@@ -18,9 +18,9 @@ use libc::{c_uint, c_char};
 use rustc::ty::TyCtxt;
 use rustc::ty::layout::{Align, Size};
 use rustc::session::{config, Session};
+use rustc_data_structures::small_c_str::SmallCStr;
 
 use std::borrow::Cow;
-use std::ffi::CString;
 use std::ops::Range;
 use std::ptr;
 
@@ -58,7 +58,7 @@ impl Builder<'a, 'll, 'tcx> {
     pub fn new_block<'b>(cx: &'a CodegenCx<'ll, 'tcx>, llfn: &'ll Value, name: &'b str) -> Self {
         let bx = Builder::with_cx(cx);
         let llbb = unsafe {
-            let name = CString::new(name).unwrap();
+            let name = SmallCStr::new(name);
             llvm::LLVMAppendBasicBlockInContext(
                 cx.llcx,
                 llfn,
@@ -118,7 +118,7 @@ impl Builder<'a, 'll, 'tcx> {
     }
 
     pub fn set_value_name(&self, value: &'ll Value, name: &str) {
-        let cname = CString::new(name.as_bytes()).unwrap();
+        let cname = SmallCStr::new(name);
         unsafe {
             llvm::LLVMSetValueName(value, cname.as_ptr());
         }
@@ -436,7 +436,7 @@ impl Builder<'a, 'll, 'tcx> {
             let alloca = if name.is_empty() {
                 llvm::LLVMBuildAlloca(self.llbuilder, ty, noname())
             } else {
-                let name = CString::new(name).unwrap();
+                let name = SmallCStr::new(name);
                 llvm::LLVMBuildAlloca(self.llbuilder, ty,
                                       name.as_ptr())
             };
@@ -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/context.rs

@@ -26,6 +26,7 @@ use type_::Type;
 use type_of::PointeeInfo;
 
 use rustc_data_structures::base_n;
+use rustc_data_structures::small_c_str::SmallCStr;
 use rustc::mir::mono::Stats;
 use rustc::session::config::{self, DebugInfo};
 use rustc::session::Session;
@@ -34,7 +35,7 @@ use rustc::ty::{self, Ty, TyCtxt};
 use rustc::util::nodemap::FxHashMap;
 use rustc_target::spec::{HasTargetSpec, Target};
 
-use std::ffi::{CStr, CString};
+use std::ffi::CStr;
 use std::cell::{Cell, RefCell};
 use std::iter;
 use std::str;
@@ -161,7 +162,7 @@ pub unsafe fn create_module(
     llcx: &'ll llvm::Context,
     mod_name: &str,
 ) -> &'ll llvm::Module {
-    let mod_name = CString::new(mod_name).unwrap();
+    let mod_name = SmallCStr::new(mod_name);
     let llmod = llvm::LLVMModuleCreateWithNameInContext(mod_name.as_ptr(), llcx);
 
     // Ensure the data-layout values hardcoded remain the defaults.
@@ -201,11 +202,10 @@ pub unsafe fn create_module(
         }
     }
 
-    let data_layout = CString::new(&sess.target.target.data_layout[..]).unwrap();
+    let data_layout = SmallCStr::new(&sess.target.target.data_layout);
     llvm::LLVMSetDataLayout(llmod, data_layout.as_ptr());
 
-    let llvm_target = sess.target.target.llvm_target.as_bytes();
-    let llvm_target = CString::new(llvm_target).unwrap();
+    let llvm_target = SmallCStr::new(&sess.target.target.llvm_target);
     llvm::LLVMRustSetNormalizedTarget(llmod, llvm_target.as_ptr());
 
     if is_pie_binary(sess) {