Remove the AllocId from ByRef values

`ByRef` const values have no identity beyond their value, we should not treat them as having identity. The `AllocId` often differed between equal constants, because of the way that the miri-engine evaluates constants.

Author: oli-obk

src/librustc/mir/interpret/value.rs

@@ -43,14 +43,13 @@ pub enum ConstValue<'tcx> {
         end: usize,
     },
 
-    /// An allocation together with a pointer into the allocation.
-    /// Invariant: the pointer's `AllocId` resolves to the allocation.
+    /// An allocation together with an offset into the allocation.
     /// The alignment exists to allow `const_field` to have `ByRef` access to nonprimitive fields
     /// of `repr(packed)` structs. The alignment may be lower than the type of this constant.
     /// This permits reads with lower alignment than what the type would normally require.
     /// FIXME(RalfJ,oli-obk): The alignment checks are part of miri, but const eval doesn't really
     /// need them. Disabling them may be too hard though.
-    ByRef(Pointer, Align, &'tcx Allocation),
+    ByRef(Size, Align, &'tcx Allocation),
 
     /// Used in the HIR by using `Unevaluated` everywhere and later normalizing to one of the other
     /// variants when the code is monomorphic enough for that.

src/librustc/ty/structural_impls.rs

@@ -1335,7 +1335,7 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::Const<'tcx> {
 impl<'tcx> TypeFoldable<'tcx> for ConstValue<'tcx> {
     fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
         match *self {
-            ConstValue::ByRef(ptr, align, alloc) => ConstValue::ByRef(ptr, align, alloc),
+            ConstValue::ByRef(offset, align, alloc) => ConstValue::ByRef(offset, align, alloc),
             ConstValue::Infer(ic) => ConstValue::Infer(ic.fold_with(folder)),
             ConstValue::Param(p) => ConstValue::Param(p.fold_with(folder)),
             ConstValue::Placeholder(p) => ConstValue::Placeholder(p),

src/librustc_codegen_llvm/consts.rs

@@ -71,7 +71,7 @@ pub fn codegen_static_initializer(
     let static_ = cx.tcx.const_eval(param_env.and(cid))?;
 
     let alloc = match static_.val {
-        ConstValue::ByRef(ptr, align, alloc) if ptr.offset.bytes() == 0 && align == alloc.align => {
+        ConstValue::ByRef(offset, align, alloc) if offset.bytes() == 0 && align == alloc.align => {
             alloc
         },
         _ => bug!("static const eval returned {:#?}", static_),

src/librustc_codegen_ssa/mir/operand.rs

@@ -109,8 +109,8 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
                 let b_llval = bx.const_usize((end - start) as u64);
                 OperandValue::Pair(a_llval, b_llval)
             },
-            ConstValue::ByRef(ptr, align, alloc) => {
-                return bx.load_operand(bx.from_const_alloc(layout, align, alloc, ptr.offset));
+            ConstValue::ByRef(offset, align, alloc) => {
+                return bx.load_operand(bx.from_const_alloc(layout, align, alloc, offset));
             },
         };
 

src/librustc_codegen_ssa/mir/place.rs

@@ -424,8 +424,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 let layout = cx.layout_of(self.monomorphize(&ty));
                 match bx.tcx().const_eval(param_env.and(cid)) {
                     Ok(val) => match val.val {
-                        mir::interpret::ConstValue::ByRef(ptr, align, alloc) => {
-                            bx.cx().from_const_alloc(layout, align, alloc, ptr.offset)
+                        mir::interpret::ConstValue::ByRef(offset, align, alloc) => {
+                            bx.cx().from_const_alloc(layout, align, alloc, offset)
                         }
                         _ => bug!("promoteds should have an allocation: {:?}", val),
                     },

src/librustc_mir/const_eval.rs

@@ -99,7 +99,7 @@ fn op_to_const<'tcx>(
         Ok(mplace) => {
             let ptr = mplace.ptr.to_ptr().unwrap();
             let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
-            ConstValue::ByRef(ptr, mplace.align, alloc)
+            ConstValue::ByRef(ptr.offset, mplace.align, alloc)
         },
         // see comment on `let try_as_immediate` above
         Err(ImmTy { imm: Immediate::Scalar(x), .. }) => match x {
@@ -113,7 +113,7 @@ fn op_to_const<'tcx>(
                 let mplace = op.to_mem_place();
                 let ptr = mplace.ptr.to_ptr().unwrap();
                 let alloc = ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id);
-                ConstValue::ByRef(ptr, mplace.align, alloc)
+                ConstValue::ByRef(ptr.offset, mplace.align, alloc)
             },
         },
         Err(ImmTy { imm: Immediate::ScalarPair(a, b), .. }) => {
@@ -542,7 +542,7 @@ fn validate_and_turn_into_const<'tcx>(
             let ptr = mplace.ptr.to_ptr()?;
             Ok(tcx.mk_const(ty::Const {
                 val: ConstValue::ByRef(
-                    ptr,
+                    ptr.offset,
                     mplace.align,
                     ecx.tcx.alloc_map.lock().unwrap_memory(ptr.alloc_id),
                 ),

src/librustc_mir/hair/pattern/_match.rs

@@ -218,7 +218,7 @@ impl LiteralExpander<'tcx> {
             (ConstValue::Scalar(Scalar::Ptr(p)), x, y) if x == y => {
                 let alloc = self.tcx.alloc_map.lock().unwrap_memory(p.alloc_id);
                 ConstValue::ByRef(
-                    p,
+                    p.offset,
                     // FIXME(oli-obk): this should be the type's layout
                     alloc.align,
                     alloc,
@@ -1436,9 +1436,10 @@ fn slice_pat_covered_by_const<'tcx>(
     suffix: &[Pattern<'tcx>],
 ) -> Result<bool, ErrorReported> {
     let data: &[u8] = match (const_val.val, &const_val.ty.sty) {
-        (ConstValue::ByRef(ptr, _, alloc), ty::Array(t, n)) => {
+        (ConstValue::ByRef(offset, _, alloc), ty::Array(t, n)) => {
             assert_eq!(*t, tcx.types.u8);
             let n = n.assert_usize(tcx).unwrap();
+            let ptr = Pointer::new(AllocId(0), offset);
             alloc.get_bytes(&tcx, ptr, Size::from_bytes(n)).unwrap()
         },
         (ConstValue::Slice { data, start, end }, ty::Slice(t)) => {
@@ -1758,9 +1759,9 @@ fn specialize<'p, 'a: 'p, 'tcx>(
                     let (alloc, offset, n, ty) = match value.ty.sty {
                         ty::Array(t, n) => {
                             match value.val {
-                                ConstValue::ByRef(ptr, _, alloc) => (
+                                ConstValue::ByRef(offset, _, alloc) => (
                                     alloc,
-                                    ptr.offset,
+                                    offset,
                                     n.unwrap_usize(cx.tcx),
                                     t,
                                 ),

src/librustc_mir/interpret/operand.rs

@@ -538,10 +538,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpretCx<'mir, 'tcx, M> {
             self.layout_of(self.monomorphize(val.ty)?)
         })?;
         let op = match val.val {
-            ConstValue::ByRef(ptr, align, _alloc) => {
+            ConstValue::ByRef(offset, align, alloc) => {
+                let id = self.tcx.alloc_map.lock().create_memory_alloc(alloc);
                 // We rely on mutability being set correctly in that allocation to prevent writes
                 // where none should happen.
-                let ptr = self.tag_static_base_pointer(ptr);
+                let ptr = self.tag_static_base_pointer(Pointer::new(id, offset));
                 Operand::Indirect(MemPlace::from_ptr(ptr, align))
             },
             ConstValue::Scalar(x) =>

src/test/incremental/simd_intrinsic_ice.rs

@@ -0,0 +1,17 @@
+#![feature(repr_simd, platform_intrinsics)]
+
+// revisions:rpass1 rpass2
+
+#[repr(simd)]
+struct I32x2(i32, i32);
+
+extern "platform-intrinsic" {
+    fn simd_shuffle2<T, U>(x: T, y: T, idx: [u32; 2]) -> U;
+}
+
+fn main() {
+    unsafe {
+        let _: I32x2 = simd_shuffle2(I32x2(1, 2), I32x2(3, 4), [0, 0]);
+        let _: I32x2 = simd_shuffle2(I32x2(1, 2), I32x2(3, 4), [0, 0]);
+    }
+}