diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs index 009e7e2487b66..043123fcab2cb 100644 --- a/compiler/rustc_codegen_llvm/src/abi.rs +++ b/compiler/rustc_codegen_llvm/src/abi.rs @@ -24,6 +24,7 @@ use crate::attributes::{self, llfn_attrs_from_instance}; use crate::builder::Builder; use crate::context::CodegenCx; use crate::llvm::{self, Attribute, AttributePlace}; +use crate::llvm_util; use crate::type_::Type; use crate::type_of::LayoutLlvmExt; use crate::value::Value; @@ -500,7 +501,16 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> { } } PassMode::Indirect { attrs, meta_attrs: None, on_stack: false } => { - apply(attrs); + let i = apply(attrs); + if cx.sess().opts.optimize != config::OptLevel::No + && llvm_util::get_version() >= (21, 0, 0) + { + attributes::apply_to_llfn( + llfn, + llvm::AttributePlace::Argument(i), + &[llvm::AttributeKind::DeadOnReturn.create_attr(cx.llcx)], + ); + } } PassMode::Indirect { attrs, meta_attrs: Some(meta_attrs), on_stack } => { assert!(!on_stack); diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs index 75d3d27f74e10..ad3c3d5932eef 100644 --- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs +++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs @@ -249,6 +249,7 @@ pub(crate) enum AttributeKind { FnRetThunkExtern = 41, Writable = 42, DeadOnUnwind = 43, + DeadOnReturn = 44, } /// LLVMIntPredicate diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp index 588d867bbbf4e..cd4f80f808c65 100644 --- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp +++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp @@ -277,6 +277,7 @@ enum class LLVMRustAttributeKind { FnRetThunkExtern = 41, Writable = 42, DeadOnUnwind = 43, + DeadOnReturn = 44, }; static Attribute::AttrKind fromRust(LLVMRustAttributeKind Kind) { @@ -369,6 +370,12 @@ static Attribute::AttrKind fromRust(LLVMRustAttributeKind Kind) { return Attribute::Writable; case LLVMRustAttributeKind::DeadOnUnwind: return Attribute::DeadOnUnwind; + case LLVMRustAttributeKind::DeadOnReturn: +#if LLVM_VERSION_GE(21, 0) + return Attribute::DeadOnReturn; +#else + report_fatal_error("DeadOnReturn attribute requires LLVM 21 or later"); +#endif } report_fatal_error("bad LLVMRustAttributeKind"); } diff --git a/tests/codegen-llvm/addr-of-mutate.rs b/tests/codegen-llvm/addr-of-mutate.rs index 14bc4b8ab28ce..7166906528939 100644 --- a/tests/codegen-llvm/addr-of-mutate.rs +++ b/tests/codegen-llvm/addr-of-mutate.rs @@ -5,7 +5,7 @@ // Test for the absence of `readonly` on the argument when it is mutated via `&raw const`. // See . -// CHECK: i8 @foo(ptr noalias{{( nocapture)?}} noundef align 1{{( captures\(none\))?}} dereferenceable(128) %x) +// CHECK: i8 @foo(ptr{{( dead_on_return)?}} noalias{{( nocapture)?}} noundef align 1{{( captures\(none\))?}} dereferenceable(128) %x) #[no_mangle] pub fn foo(x: [u8; 128]) -> u8 { let ptr = core::ptr::addr_of!(x).cast_mut(); @@ -15,7 +15,7 @@ pub fn foo(x: [u8; 128]) -> u8 { x[0] } -// CHECK: i1 @second(ptr noalias{{( nocapture)?}} noundef align {{[0-9]+}}{{( captures\(none\))?}} dereferenceable({{[0-9]+}}) %a_ptr_and_b) +// CHECK: i1 @second(ptr{{( dead_on_return)?}} noalias{{( nocapture)?}} noundef align {{[0-9]+}}{{( captures\(none\))?}} dereferenceable({{[0-9]+}}) %a_ptr_and_b) #[no_mangle] pub unsafe fn second(a_ptr_and_b: (*mut (i32, bool), (i64, bool))) -> bool { let b_bool_ptr = core::ptr::addr_of!(a_ptr_and_b.1.1).cast_mut(); @@ -24,7 +24,7 @@ pub unsafe fn second(a_ptr_and_b: (*mut (i32, bool), (i64, bool))) -> bool { } // If going through a deref (and there are no other mutating accesses), then `readonly` is fine. -// CHECK: i1 @third(ptr noalias{{( nocapture)?}} noundef readonly align {{[0-9]+}}{{( captures\(none\))?}} dereferenceable({{[0-9]+}}) %a_ptr_and_b) +// CHECK: i1 @third(ptr{{( dead_on_return)?}} noalias{{( nocapture)?}} noundef readonly align {{[0-9]+}}{{( captures\(none\))?}} dereferenceable({{[0-9]+}}) %a_ptr_and_b) #[no_mangle] pub unsafe fn third(a_ptr_and_b: (*mut (i32, bool), (i64, bool))) -> bool { let b_bool_ptr = core::ptr::addr_of!((*a_ptr_and_b.0).1).cast_mut(); diff --git a/tests/codegen-llvm/dead_on_return.rs b/tests/codegen-llvm/dead_on_return.rs new file mode 100644 index 0000000000000..3c1940d6ba7c9 --- /dev/null +++ b/tests/codegen-llvm/dead_on_return.rs @@ -0,0 +1,31 @@ +//@ compile-flags: -C opt-level=3 +//@ min-llvm-version: 21 + +#![crate_type = "lib"] +#![allow(unused_assignments, unused_variables)] + +// Check that the old string is deallocated, but a new one is not initialized. +#[unsafe(no_mangle)] +pub fn test_str_new(mut s: String) { + // CHECK-LABEL: @test_str_new + // CHECK: __rust_dealloc + // CHECK-NOT: store + s = String::new(); +} + +#[unsafe(no_mangle)] +pub fn test_str_take(mut x: String) -> String { + // CHECK-LABEL: @test_str_take + // CHECK-NEXT: {{.*}}: + // CHECK-NEXT: call void @llvm.memcpy + // CHECK-NEXT: ret + core::mem::take(&mut x) +} + +#[unsafe(no_mangle)] +pub fn test_array_store(mut x: [u32; 100]) { + // CHECK-LABEL: @test_array_store + // CHECK-NEXT: {{.*}}: + // CHECK-NEXT: ret + x[0] = 1; +} diff --git a/tests/codegen-llvm/function-arguments.rs b/tests/codegen-llvm/function-arguments.rs index c8cd8526ae513..a3fafbe6f821c 100644 --- a/tests/codegen-llvm/function-arguments.rs +++ b/tests/codegen-llvm/function-arguments.rs @@ -134,7 +134,7 @@ pub fn mutable_notunpin_borrow(_: &mut NotUnpin) {} #[no_mangle] pub fn notunpin_borrow(_: &NotUnpin) {} -// CHECK: @indirect_struct(ptr noalias{{( nocapture)?}} noundef readonly align 4{{( captures\(none\))?}} dereferenceable(32) %_1) +// CHECK: @indirect_struct(ptr{{( dead_on_return)?}} noalias{{( nocapture)?}} noundef readonly align 4{{( captures\(none\))?}} dereferenceable(32) %_1) #[no_mangle] pub fn indirect_struct(_: S) {} diff --git a/tests/codegen-llvm/loongarch-abi/loongarch64-lp64d-abi.rs b/tests/codegen-llvm/loongarch-abi/loongarch64-lp64d-abi.rs index 93c8d60930b75..4666342a16a31 100644 --- a/tests/codegen-llvm/loongarch-abi/loongarch64-lp64d-abi.rs +++ b/tests/codegen-llvm/loongarch-abi/loongarch64-lp64d-abi.rs @@ -256,7 +256,7 @@ pub struct IntDoubleInt { c: i32, } -// CHECK: define void @f_int_double_int_s_arg(ptr noalias{{( nocapture)?}} noundef align 8{{( captures\(none\))?}} dereferenceable(24) %a) +// CHECK: define void @f_int_double_int_s_arg(ptr{{( dead_on_return)?}} noalias{{( nocapture)?}} noundef align 8{{( captures\(none\))?}} dereferenceable(24) %a) #[no_mangle] pub extern "C" fn f_int_double_int_s_arg(a: IntDoubleInt) {}