Nul terminate rust string literals

bjorn3 · bjorn3 · commit d42a6621e9e6 · 2025-03-17T12:33:44.000Z
This allows taking advantage of the C string merging functionality of
linkers, reducing code size.
diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -24,10 +24,17 @@ use super::{
 use crate::fluent_generated as fluent;
 
 /// Directly returns an `Allocation` containing an absolute path representation of the given type.
-pub(crate) fn alloc_type_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> ConstAllocation<'tcx> {
-    let path = crate::util::type_name(tcx, ty);
+pub(crate) fn alloc_type_name<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    ty: Ty<'tcx>,
+) -> (ConstAllocation<'tcx>, u64) {
+    let mut path = crate::util::type_name(tcx, ty);
+    let path_len = path.len().try_into().unwrap();
+    if !path.contains('\0') {
+        path.push('\0');
+    };
     let alloc = Allocation::from_bytes_byte_aligned_immutable(path.into_bytes());
-    tcx.mk_const_alloc(alloc)
+    (tcx.mk_const_alloc(alloc), path_len)
 }
 
 /// The logic for all nullary intrinsics is implemented here. These intrinsics don't get evaluated
@@ -43,8 +50,8 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
     interp_ok(match name {
         sym::type_name => {
             ensure_monomorphic_enough(tcx, tp_ty)?;
-            let alloc = alloc_type_name(tcx, tp_ty);
-            ConstValue::Slice { data: alloc, meta: alloc.inner().size().bytes() }
+            let (alloc, path_len) = alloc_type_name(tcx, tp_ty);
+            ConstValue::Slice { data: alloc, meta: path_len }
         }
         sym::needs_drop => {
             ensure_monomorphic_enough(tcx, tp_ty)?;
diff --git a/compiler/rustc_const_eval/src/interpret/place.rs b/compiler/rustc_const_eval/src/interpret/place.rs
@@ -1019,11 +1019,16 @@ where
         &mut self,
         s: &str,
     ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::Provenance>> {
-        let bytes = s.as_bytes();
-        let ptr = self.allocate_bytes_dedup(bytes)?;
+        let ptr = if !s.contains('\0') {
+            let mut bytes = s.as_bytes().to_owned();
+            bytes.push(0);
+            self.allocate_bytes_dedup(&bytes)?
+        } else {
+            self.allocate_bytes_dedup(s.as_bytes())?
+        };
 
         // Create length metadata for the string.
-        let meta = Scalar::from_target_usize(u64::try_from(bytes.len()).unwrap(), self);
+        let meta = Scalar::from_target_usize(u64::try_from(s.len()).unwrap(), self);
 
         // Get layout for Rust's str type.
         let layout = self.layout_of(self.tcx.types.str_).unwrap();
diff --git a/compiler/rustc_mir_build/src/builder/expr/as_constant.rs b/compiler/rustc_mir_build/src/builder/expr/as_constant.rs
@@ -125,9 +125,15 @@ fn lit_to_mir_constant<'tcx>(tcx: TyCtxt<'tcx>, lit_input: LitToConstInput<'tcx>
     let value = match (lit, lit_ty.kind()) {
         (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
             let s = s.as_str();
-            let allocation = Allocation::from_bytes_byte_aligned_immutable(s.as_bytes());
+            let allocation = if !s.contains('\0') {
+                let mut s = s.to_owned();
+                s.push('\0');
+                Allocation::from_bytes_byte_aligned_immutable(s.as_bytes())
+            } else {
+                Allocation::from_bytes_byte_aligned_immutable(s.as_bytes())
+            };
             let allocation = tcx.mk_const_alloc(allocation);
-            ConstValue::Slice { data: allocation, meta: allocation.inner().size().bytes() }
+            ConstValue::Slice { data: allocation, meta: s.len().try_into().unwrap() }
         }
         (ast::LitKind::ByteStr(data, _), ty::Ref(_, inner_ty, _))
             if matches!(inner_ty.kind(), ty::Slice(_)) =>
diff --git a/tests/codegen/remap_path_prefix/main.rs b/tests/codegen/remap_path_prefix/main.rs
@@ -12,7 +12,7 @@ mod aux_mod;
 include!("aux_mod.rs");
 
 // Here we check that the expansion of the file!() macro is mapped.
-// CHECK: @alloc_5761061597a97f66e13ef2ff92712c4b = private unnamed_addr constant [34 x i8] c"/the/src/remap_path_prefix/main.rs"
+// CHECK: @alloc_4079a2e7607f89f86df6b8a72ba0dd06 = private unnamed_addr constant [35 x i8] c"/the/src/remap_path_prefix/main.rs\00"
 pub static FILE_PATH: &'static str = file!();
 
 fn main() {
diff --git a/tests/mir-opt/const_allocation.main.GVN.after.32bit.mir b/tests/mir-opt/const_allocation.main.GVN.after.32bit.mir
@@ -33,27 +33,27 @@ ALLOC2 (size: 16, align: 4) {
     ╾ALLOC4<imm>╼ 03 00 00 00 ╾ALLOC5<imm>╼ 03 00 00 00 │ ╾──╼....╾──╼....
 }
 
-ALLOC4 (size: 3, align: 1) {
-    66 6f 6f                                        │ foo
+ALLOC4 (size: 4, align: 1) {
+    66 6f 6f 00                                     │ foo.
 }
 
-ALLOC5 (size: 3, align: 1) {
-    62 61 72                                        │ bar
+ALLOC5 (size: 4, align: 1) {
+    62 61 72 00                                     │ bar.
 }
 
 ALLOC3 (size: 24, align: 4) {
     0x00 │ ╾ALLOC6<imm>╼ 03 00 00 00 ╾ALLOC7<imm>╼ 03 00 00 00 │ ╾──╼....╾──╼....
     0x10 │ ╾ALLOC8<imm>╼ 04 00 00 00                         │ ╾──╼....
 }
 
-ALLOC6 (size: 3, align: 1) {
-    6d 65 68                                        │ meh
+ALLOC6 (size: 4, align: 1) {
+    6d 65 68 00                                     │ meh.
 }
 
-ALLOC7 (size: 3, align: 1) {
-    6d 6f 70                                        │ mop
+ALLOC7 (size: 4, align: 1) {
+    6d 6f 70 00                                     │ mop.
 }
 
-ALLOC8 (size: 4, align: 1) {
-    6d c3 b6 70                                     │ m..p
+ALLOC8 (size: 5, align: 1) {
+    6d c3 b6 70 00                                  │ m..p.
 }
diff --git a/tests/mir-opt/const_allocation.main.GVN.after.64bit.mir b/tests/mir-opt/const_allocation.main.GVN.after.64bit.mir
@@ -36,12 +36,12 @@ ALLOC2 (size: 32, align: 8) {
     0x10 │ ╾ALLOC5<imm>╼ 03 00 00 00 00 00 00 00 │ ╾──────╼........
 }
 
-ALLOC4 (size: 3, align: 1) {
-    66 6f 6f                                        │ foo
+ALLOC4 (size: 4, align: 1) {
+    66 6f 6f 00                                     │ foo.
 }
 
-ALLOC5 (size: 3, align: 1) {
-    62 61 72                                        │ bar
+ALLOC5 (size: 4, align: 1) {
+    62 61 72 00                                     │ bar.
 }
 
 ALLOC3 (size: 48, align: 8) {
@@ -50,14 +50,14 @@ ALLOC3 (size: 48, align: 8) {
     0x20 │ ╾ALLOC8<imm>╼ 04 00 00 00 00 00 00 00 │ ╾──────╼........
 }
 
-ALLOC6 (size: 3, align: 1) {
-    6d 65 68                                        │ meh
+ALLOC6 (size: 4, align: 1) {
+    6d 65 68 00                                     │ meh.
 }
 
-ALLOC7 (size: 3, align: 1) {
-    6d 6f 70                                        │ mop
+ALLOC7 (size: 4, align: 1) {
+    6d 6f 70 00                                     │ mop.
 }
 
-ALLOC8 (size: 4, align: 1) {
-    6d c3 b6 70                                     │ m..p
+ALLOC8 (size: 5, align: 1) {
+    6d c3 b6 70 00                                  │ m..p.
 }
diff --git a/tests/ui-fulldeps/stable-mir/check_allocation.rs b/tests/ui-fulldeps/stable-mir/check_allocation.rs
@@ -19,13 +19,6 @@ extern crate rustc_driver;
 extern crate rustc_interface;
 extern crate stable_mir;
 
-use rustc_smir::rustc_internal;
-use stable_mir::crate_def::CrateDef;
-use stable_mir::mir::alloc::GlobalAlloc;
-use stable_mir::mir::mono::{Instance, InstanceKind, StaticDef};
-use stable_mir::mir::{Body, TerminatorKind};
-use stable_mir::ty::{Allocation, ConstantKind, RigidTy, TyKind};
-use stable_mir::{CrateItem, CrateItems, ItemKind};
 use std::ascii::Char;
 use std::assert_matches::assert_matches;
 use std::cmp::{max, min};
@@ -34,6 +27,14 @@ use std::ffi::CStr;
 use std::io::Write;
 use std::ops::ControlFlow;
 
+use rustc_smir::rustc_internal;
+use stable_mir::crate_def::CrateDef;
+use stable_mir::mir::alloc::GlobalAlloc;
+use stable_mir::mir::mono::{Instance, InstanceKind, StaticDef};
+use stable_mir::mir::{Body, TerminatorKind};
+use stable_mir::ty::{Allocation, ConstantKind, RigidTy, TyKind};
+use stable_mir::{CrateItem, CrateItems, ItemKind};
+
 const CRATE_NAME: &str = "input";
 
 /// This function uses the Stable MIR APIs to get information about the test crate.
@@ -78,11 +79,12 @@ fn check_bar(item: CrateItem) {
 
     let alloc_id_0 = alloc.provenance.ptrs[0].1.0;
     let GlobalAlloc::Memory(allocation) = GlobalAlloc::from(alloc_id_0) else { unreachable!() };
-    assert_eq!(allocation.bytes.len(), 3);
+    assert_eq!(allocation.bytes.len(), 4);
     assert_eq!(allocation.bytes[0].unwrap(), Char::CapitalB.to_u8());
     assert_eq!(allocation.bytes[1].unwrap(), Char::SmallA.to_u8());
     assert_eq!(allocation.bytes[2].unwrap(), Char::SmallR.to_u8());
-    assert_eq!(std::str::from_utf8(&allocation.raw_bytes().unwrap()), Ok("Bar"));
+    assert_eq!(allocation.bytes[3].unwrap(), Char::Null.to_u8());
+    assert_eq!(std::str::from_utf8(&allocation.raw_bytes().unwrap()), Ok("Bar\0"));
 }
 
 /// Check the allocation data for static `C_STR`.
diff --git a/tests/ui-fulldeps/stable-mir/check_transform.rs b/tests/ui-fulldeps/stable-mir/check_transform.rs
@@ -38,7 +38,7 @@ fn test_transform() -> ControlFlow<()> {
     let target_fn = *get_item(&items, (ItemKind::Fn, "dummy")).unwrap();
     let instance = Instance::try_from(target_fn).unwrap();
     let body = instance.body().unwrap();
-    check_msg(&body, "oops");
+    check_msg(&body, "oops\0");
 
     let new_msg = "new panic message";
     let new_body = change_panic_msg(body, new_msg);

Original file line number	Diff line number	Diff line change
`@@ -33,27 +33,27 @@ ALLOC2 (size: 16, align: 4) {`
`33`	`33`	`╾ALLOC4<imm>╼ 03 00 00 00 ╾ALLOC5<imm>╼ 03 00 00 00 │ ╾──╼....╾──╼....`
`34`	`34`	`}`
`35`	`35`
`36`		`-ALLOC4 (size: 3, align: 1) {`
`37`		`- 66 6f 6f │ foo`
	`36`	`+ALLOC4 (size: 4, align: 1) {`
	`37`	`+ 66 6f 6f 00 │ foo.`
`38`	`38`	`}`
`39`	`39`
`40`		`-ALLOC5 (size: 3, align: 1) {`
`41`		`- 62 61 72 │ bar`
	`40`	`+ALLOC5 (size: 4, align: 1) {`
	`41`	`+ 62 61 72 00 │ bar.`
`42`	`42`	`}`
`43`	`43`
`44`	`44`	`ALLOC3 (size: 24, align: 4) {`
`45`	`45`	`0x00 │ ╾ALLOC6<imm>╼ 03 00 00 00 ╾ALLOC7<imm>╼ 03 00 00 00 │ ╾──╼....╾──╼....`
`46`	`46`	`0x10 │ ╾ALLOC8<imm>╼ 04 00 00 00 │ ╾──╼....`
`47`	`47`	`}`
`48`	`48`
`49`		`-ALLOC6 (size: 3, align: 1) {`
`50`		`- 6d 65 68 │ meh`
	`49`	`+ALLOC6 (size: 4, align: 1) {`
	`50`	`+ 6d 65 68 00 │ meh.`
`51`	`51`	`}`
`52`	`52`
`53`		`-ALLOC7 (size: 3, align: 1) {`
`54`		`- 6d 6f 70 │ mop`
	`53`	`+ALLOC7 (size: 4, align: 1) {`
	`54`	`+ 6d 6f 70 00 │ mop.`
`55`	`55`	`}`
`56`	`56`
`57`		`-ALLOC8 (size: 4, align: 1) {`
`58`		`- 6d c3 b6 70 │ m..p`
	`57`	`+ALLOC8 (size: 5, align: 1) {`
	`58`	`+ 6d c3 b6 70 00 │ m..p.`
`59`	`59`	`}`
Original file line number	Diff line number	Diff line change
`@@ -36,12 +36,12 @@ ALLOC2 (size: 32, align: 8) {`
`36`	`36`	`0x10 │ ╾ALLOC5<imm>╼ 03 00 00 00 00 00 00 00 │ ╾──────╼........`
`37`	`37`	`}`
`38`	`38`
`39`		`-ALLOC4 (size: 3, align: 1) {`
`40`		`- 66 6f 6f │ foo`
	`39`	`+ALLOC4 (size: 4, align: 1) {`
	`40`	`+ 66 6f 6f 00 │ foo.`
`41`	`41`	`}`
`42`	`42`
`43`		`-ALLOC5 (size: 3, align: 1) {`
`44`		`- 62 61 72 │ bar`
	`43`	`+ALLOC5 (size: 4, align: 1) {`
	`44`	`+ 62 61 72 00 │ bar.`
`45`	`45`	`}`
`46`	`46`
`47`	`47`	`ALLOC3 (size: 48, align: 8) {`
`@@ -50,14 +50,14 @@ ALLOC3 (size: 48, align: 8) {`
`50`	`50`	`0x20 │ ╾ALLOC8<imm>╼ 04 00 00 00 00 00 00 00 │ ╾──────╼........`
`51`	`51`	`}`
`52`	`52`
`53`		`-ALLOC6 (size: 3, align: 1) {`
`54`		`- 6d 65 68 │ meh`
	`53`	`+ALLOC6 (size: 4, align: 1) {`
	`54`	`+ 6d 65 68 00 │ meh.`
`55`	`55`	`}`
`56`	`56`
`57`		`-ALLOC7 (size: 3, align: 1) {`
`58`		`- 6d 6f 70 │ mop`
	`57`	`+ALLOC7 (size: 4, align: 1) {`
	`58`	`+ 6d 6f 70 00 │ mop.`
`59`	`59`	`}`
`60`	`60`
`61`		`-ALLOC8 (size: 4, align: 1) {`
`62`		`- 6d c3 b6 70 │ m..p`
	`61`	`+ALLOC8 (size: 5, align: 1) {`
	`62`	`+ 6d c3 b6 70 00 │ m..p.`
`63`	`63`	`}`