Auto merge of #116707 - cjgillot:slice-id, r=oli-obk,RalfJung

Create an `AllocId` for `ConstValue::Slice`.

This PR modifies `ConstValue::Slice` to use an `AllocId` instead of directly manipulating the allocation. This was originally proposed by https://github.com/rust-lang/rust/pull/115764 but was a perf regression.

Almost 2 years later, enough code has changed to make this a perf improvement: https://github.com/rust-lang/rust/pull/116707#issuecomment-3067158777

3 files changed, 5 insertions, 8 deletions

diff --git a/compiler/rustc_codegen_ssa/src/common.rs b/compiler/rustc_codegen_ssa/src/common.rs
index 48565e0b4de..a6fd6c763ed 100644
--- a/compiler/rustc_codegen_ssa/src/common.rs
+++ b/compiler/rustc_codegen_ssa/src/common.rs
@@ -148,7 +148,7 @@ pub(crate) fn shift_mask_val<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 pub fn asm_const_to_str<'tcx>(
     tcx: TyCtxt<'tcx>,
     sp: Span,
-    const_value: mir::ConstValue<'tcx>,
+    const_value: mir::ConstValue,
     ty_and_layout: TyAndLayout<'tcx>,
 ) -> String {
     let mir::ConstValue::Scalar(scalar) = const_value else {
diff --git a/compiler/rustc_codegen_ssa/src/mir/constant.rs b/compiler/rustc_codegen_ssa/src/mir/constant.rs
index 68a56044a07..11b6ab3cdf1 100644
--- a/compiler/rustc_codegen_ssa/src/mir/constant.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/constant.rs
@@ -20,7 +20,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         OperandRef::from_const(bx, val, ty)
     }
 
-    pub fn eval_mir_constant(&self, constant: &mir::ConstOperand<'tcx>) -> mir::ConstValue<'tcx> {
+    pub fn eval_mir_constant(&self, constant: &mir::ConstOperand<'tcx>) -> mir::ConstValue {
         // `MirUsedCollector` visited all required_consts before codegen began, so if we got here
         // there can be no more constants that fail to evaluate.
         self.monomorphize(constant.const_)
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index 06bedaaa4a2..8e308aac769 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -140,7 +140,7 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
 
     pub(crate) fn from_const<Bx: BuilderMethods<'a, 'tcx, Value = V>>(
         bx: &mut Bx,
-        val: mir::ConstValue<'tcx>,
+        val: mir::ConstValue,
         ty: Ty<'tcx>,
     ) -> Self {
         let layout = bx.layout_of(ty);
@@ -154,14 +154,11 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
                 OperandValue::Immediate(llval)
             }
             ConstValue::ZeroSized => return OperandRef::zero_sized(layout),
-            ConstValue::Slice { data, meta } => {
+            ConstValue::Slice { alloc_id, meta } => {
                 let BackendRepr::ScalarPair(a_scalar, _) = layout.backend_repr else {
                     bug!("from_const: invalid ScalarPair layout: {:#?}", layout);
                 };
-                let a = Scalar::from_pointer(
-                    Pointer::new(bx.tcx().reserve_and_set_memory_alloc(data).into(), Size::ZERO),
-                    &bx.tcx(),
-                );
+                let a = Scalar::from_pointer(Pointer::new(alloc_id.into(), Size::ZERO), &bx.tcx());
                 let a_llval = bx.scalar_to_backend(
                     a,
                     a_scalar,