diff options
| -rw-r--r-- | compiler/rustc_codegen_llvm/src/consts.rs | 5 | ||||
| -rw-r--r-- | tests/assembly/cstring-merging.rs | 27 |
2 files changed, 32 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs index a1ab6714d37..75b4ff1b6bb 100644 --- a/compiler/rustc_codegen_llvm/src/consts.rs +++ b/compiler/rustc_codegen_llvm/src/consts.rs @@ -128,6 +128,11 @@ pub(crate) fn const_alloc_to_llvm<'ll>( append_chunks_of_init_and_uninit_bytes(&mut llvals, cx, alloc, range); } + // Avoid wrapping in a struct if there is only a single value. This ensures + // that LLVM is able to perform the string merging optimization if the constant + // is a valid C string. LLVM only considers bare arrays for this optimization, + // not arrays wrapped in a struct. LLVM handles this at: + // https://github.com/rust-lang/llvm-project/blob/acaea3d2bb8f351b740db7ebce7d7a40b9e21488/llvm/lib/Target/TargetLoweringObjectFile.cpp#L249-L280 if let &[data] = &*llvals { data } else { cx.const_struct(&llvals, true) } } diff --git a/tests/assembly/cstring-merging.rs b/tests/assembly/cstring-merging.rs new file mode 100644 index 00000000000..7436e241823 --- /dev/null +++ b/tests/assembly/cstring-merging.rs @@ -0,0 +1,27 @@ +//@ only-linux +//@ assembly-output: emit-asm +//@ compile-flags: --crate-type=lib -Copt-level=3 --edition 2024 + +use std::ffi::CStr; + +// CHECK: .section .rodata.str1.1,"aMS" +// CHECK: .Lanon.{{.+}}: +// CHECK-NEXT: .asciz "foo" +#[unsafe(no_mangle)] +static CSTR: &[u8; 4] = b"foo\0"; + +// CHECK-NOT: .section +// CHECK: .Lanon.{{.+}}: +// CHECK-NEXT: .asciz "bar" +#[unsafe(no_mangle)] +pub fn cstr() -> &'static CStr { + c"bar" +} + +// CHECK-NOT: .section +// CHECK: .Lanon.{{.+}}: +// CHECK-NEXT: .asciz "baz" +#[unsafe(no_mangle)] +pub fn manual_cstr() -> &'static str { + "baz\0" +} |