Auto merge of #123425 - jieyouxu:array-imm-noundef-param, r=<try>

Add `noundef` metadata for fits-in-target-pointer-size array immediate arguments

`noundef` is only added if the small array immediate fits in the target pointer size and if optimizations are enabled.

Closes #123183.

compiler/rustc_ty_utils/src/abi.rs

@@ -8,8 +8,8 @@ use rustc_middle::ty::{self, InstanceDef, Ty, TyCtxt};
 use rustc_session::config::OptLevel;
 use rustc_span::def_id::DefId;
 use rustc_target::abi::call::{
-    ArgAbi, ArgAttribute, ArgAttributes, ArgExtension, Conv, FnAbi, PassMode, Reg, RegKind,
-    RiscvInterruptKind,
+    ArgAbi, ArgAttribute, ArgAttributes, ArgExtension, CastTarget, Conv, FnAbi, PassMode, Reg,
+    RegKind, RiscvInterruptKind,
 };
 use rustc_target::abi::*;
 use rustc_target::spec::abi::Abi as SpecAbi;
@@ -784,6 +784,29 @@ fn fn_abi_adjust_for_abi<'tcx>(
                 // an LLVM aggregate type for this leads to bad optimizations,
                 // so we pick an appropriately sized integer type instead.
                 arg.cast_to(Reg { kind: RegKind::Integer, size });
+
+                // Let's see if we can add a `noundef`. This is only legal for arrays, definitely
+                // not for unions. This is also legal for `#[repr(transparent)] struct` or
+                // `#[repr(transparent)] enum` containing array.
+                let is_transparent_array =
+                    if arg.layout.is_transparent::<LayoutCx<'tcx, TyCtxt<'tcx>>>()
+                        && let Some((_, layout)) = arg.layout.non_1zst_field(cx)
+                        && layout.ty.is_array()
+                    {
+                        true
+                    } else {
+                        false
+                    };
+
+                if arg.layout.ty.is_array() || is_transparent_array {
+                    // Fixup arg attribute with `noundef`.
+                    let PassMode::Cast { ref mut cast, .. } = &mut arg.mode else {
+                        bug!("this cannot fail because of the previous cast_to `Reg`");
+                    };
+
+                    let box CastTarget { ref mut attrs, .. } = cast;
+                    attrs.set(ArgAttribute::NoUndef);
+                }
             }
 
             // If we deduced that this parameter was read-only, add that to the attribute list now.

tests/codegen/array-immediate-param-noundef.rs

@@ -0,0 +1,95 @@
+// Check that small array immediates that fits in target pointer size in argument position have
+// `noundef` parameter metadata. Note that the `noundef` parameter metadata is only applied if:
+// - `!arg.layout.is_unsized() && size <= Pointer(AddressSpace::DATA).size(cx)`
+// - optimizations are turned on.
+//
+// ignore-tidy-linelength
+//@ only-64bit (presence of noundef depends on pointer width)
+//@ compile-flags: -C no-prepopulate-passes -O
+#![crate_type = "lib"]
+
+// CHECK: define noundef i64 @replace_short_array_u64x1(ptr noalias noundef align 8 dereferenceable(8) %r, i64 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u64x1(r: &mut [u64; 1], v: [u64; 1]) -> [u64; 1] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i32 @replace_short_array_u32x1(ptr noalias noundef align 4 dereferenceable(4) %r, i32 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u32x1(r: &mut [u32; 1], v: [u32; 1]) -> [u32; 1] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i64 @replace_short_array_u32x2(ptr noalias noundef align 4 dereferenceable(8) %r, i64 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u32x2(r: &mut [u32; 2], v: [u32; 2]) -> [u32; 2] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i16 @replace_short_array_u16x1(ptr noalias noundef align 2 dereferenceable(2) %r, i16 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u16x1(r: &mut [u16; 1], v: [u16; 1]) -> [u16; 1] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i32 @replace_short_array_u16x2(ptr noalias noundef align 2 dereferenceable(4) %r, i32 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u16x2(r: &mut [u16; 2], v: [u16; 2]) -> [u16; 2] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i48 @replace_short_array_u16x3(ptr noalias noundef align 2 dereferenceable(6) %r, i48 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u16x3(r: &mut [u16; 3], v: [u16; 3]) -> [u16; 3] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i64 @replace_short_array_u16x4(ptr noalias noundef align 2 dereferenceable(8) %r, i64 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u16x4(r: &mut [u16; 4], v: [u16; 4]) -> [u16; 4] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i8 @replace_short_array_u8x1(ptr noalias noundef align 1 dereferenceable(1) %r, i8 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u8x1(r: &mut [u8; 1], v: [u8; 1]) -> [u8; 1] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i16 @replace_short_array_u8x2(ptr noalias noundef align 1 dereferenceable(2) %r, i16 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u8x2(r: &mut [u8; 2], v: [u8; 2]) -> [u8; 2] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i24 @replace_short_array_u8x3(ptr noalias noundef align 1 dereferenceable(3) %r, i24 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u8x3(r: &mut [u8; 3], v: [u8; 3]) -> [u8; 3] {
+    std::mem::replace(r, v)
+}
+
+// CHECK: define noundef i64 @replace_short_array_u8x8(ptr noalias noundef align 1 dereferenceable(8) %r, i64 noundef %0)
+#[no_mangle]
+pub fn replace_short_array_u8x8(r: &mut [u8; 8], v: [u8; 8]) -> [u8; 8] {
+    std::mem::replace(r, v)
+}
+
+#[repr(transparent)]
+pub struct Foo([u8; 4]);
+
+// CHECK: define noundef i32 @replace_repr_transparent_struct_short_array(ptr noalias noundef align 1 dereferenceable(4) %r, i32 noundef %0)
+#[no_mangle]
+pub fn replace_repr_transparent_struct_short_array(r: &mut Foo, v: Foo) -> Foo {
+    std::mem::replace(r, v)
+}
+
+#[repr(transparent)]
+pub enum Bar {
+    Default([u8; 4])
+}
+
+// CHECK: define noundef i32 @replace_repr_transparent_enum_short_array(ptr noalias noundef align 1 dereferenceable(4) %r, i32 noundef %0)
+#[no_mangle]
+pub fn replace_repr_transparent_enum_short_array(r: &mut Bar, v: Bar) -> Bar {
+    std::mem::replace(r, v)
+}