Rollup merge of rust-lang#58511 - oli-obk:const_to_op, r=RalfJung

Const to op simplification

r? @RalfJung

alternative to rust-lang#58486

src/librustc/ich/impls_ty.rs

@@ -312,7 +312,7 @@ impl_stable_hash_for!(
     impl<'tcx> for enum mir::interpret::ConstValue<'tcx> [ mir::interpret::ConstValue ] {
         Scalar(val),
         Slice(a, b),
-        ByRef(id, alloc, offset),
+        ByRef(ptr, alloc),
     }
 );
 impl_stable_hash_for!(struct crate::mir::interpret::RawConst<'tcx> {

src/librustc/mir/interpret/value.rs

@@ -31,9 +31,9 @@ pub enum ConstValue<'tcx> {
     /// it.
     Slice(Scalar, u64),
 
-    /// An allocation together with an offset into the allocation.
-    /// Invariant: the `AllocId` matches the allocation.
-    ByRef(AllocId, &'tcx Allocation, Size),
+    /// An allocation together with a pointer into the allocation.
+    /// Invariant: the pointer's `AllocId` resolves to the allocation.
+    ByRef(Pointer, &'tcx Allocation),
 }
 
 #[cfg(target_arch = "x86_64")]

src/librustc/ty/structural_impls.rs

@@ -505,8 +505,8 @@ impl<'a, 'tcx> Lift<'tcx> for ConstValue<'a> {
         match *self {
             ConstValue::Scalar(x) => Some(ConstValue::Scalar(x)),
             ConstValue::Slice(x, y) => Some(ConstValue::Slice(x, y)),
-            ConstValue::ByRef(x, alloc, z) => Some(ConstValue::ByRef(
-                x, alloc.lift_to_tcx(tcx)?, z,
+            ConstValue::ByRef(ptr, alloc) => Some(ConstValue::ByRef(
+                ptr, alloc.lift_to_tcx(tcx)?,
             )),
         }
     }

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(_, alloc, n) if n.bytes() == 0 => alloc,
+        ConstValue::ByRef(ptr, alloc) if ptr.offset.bytes() == 0 => alloc,
         _ => bug!("static const eval returned {:#?}", static_),
     };
     Ok((const_alloc_to_llvm(cx, alloc), alloc))

src/librustc_codegen_ssa/mir/operand.rs

@@ -101,8 +101,8 @@ impl<'a, 'tcx: 'a, V: CodegenObject> OperandRef<'tcx, V> {
                 let b_llval = bx.cx().const_usize(b);
                 OperandValue::Pair(a_llval, b_llval)
             },
-            ConstValue::ByRef(_, alloc, offset) => {
-                return Ok(bx.load_operand(bx.cx().from_const_alloc(layout, alloc, offset)));
+            ConstValue::ByRef(ptr, alloc) => {
+                return Ok(bx.load_operand(bx.cx().from_const_alloc(layout, alloc, ptr.offset)));
             },
         };
 

src/librustc_codegen_ssa/mir/place.rs

@@ -417,8 +417,8 @@ impl<'a, 'tcx: 'a, 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(_, alloc, offset) => {
-                            bx.cx().from_const_alloc(layout, alloc, offset)
+                        mir::interpret::ConstValue::ByRef(ptr, alloc) => {
+                            bx.cx().from_const_alloc(layout, alloc, ptr.offset)
                         }
                         _ => bug!("promoteds should have an allocation: {:?}", val),
                     },

src/librustc_mir/const_eval.rs

@@ -21,7 +21,7 @@ use syntax::ast::Mutability;
 use syntax::source_map::{Span, DUMMY_SP};
 
 use crate::interpret::{self,
-    PlaceTy, MPlaceTy, MemPlace, OpTy, ImmTy, Operand, Immediate, Scalar, Pointer,
+    PlaceTy, MPlaceTy, MemPlace, OpTy, ImmTy, Immediate, Scalar, Pointer,
     RawConst, ConstValue,
     EvalResult, EvalError, EvalErrorKind, GlobalId, EvalContext, StackPopCleanup,
     Allocation, AllocId, MemoryKind,
@@ -62,45 +62,46 @@ pub(crate) fn eval_promoted<'a, 'mir, 'tcx>(
     eval_body_using_ecx(&mut ecx, cid, Some(mir), param_env)
 }
 
-// FIXME: These two conversion functions are bad hacks.  We should just always use allocations.
-pub fn op_to_const<'tcx>(
+fn mplace_to_const<'tcx>(
+    ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
+    mplace: MPlaceTy<'tcx>,
+) -> EvalResult<'tcx, ty::Const<'tcx>> {
+    let MemPlace { ptr, align, meta } = *mplace;
+    // extract alloc-offset pair
+    assert!(meta.is_none());
+    let ptr = ptr.to_ptr()?;
+    let alloc = ecx.memory.get(ptr.alloc_id)?;
+    assert!(alloc.align >= align);
+    assert!(alloc.bytes.len() as u64 - ptr.offset.bytes() >= mplace.layout.size.bytes());
+    let mut alloc = alloc.clone();
+    alloc.align = align;
+    // FIXME shouldn't it be the case that `mark_static_initialized` has already
+    // interned this?  I thought that is the entire point of that `FinishStatic` stuff?
+    let alloc = ecx.tcx.intern_const_alloc(alloc);
+    let val = ConstValue::ByRef(ptr, alloc);
+    Ok(ty::Const { val, ty: mplace.layout.ty })
+}
+
+fn op_to_const<'tcx>(
     ecx: &CompileTimeEvalContext<'_, '_, 'tcx>,
     op: OpTy<'tcx>,
-    may_normalize: bool,
 ) -> EvalResult<'tcx, ty::Const<'tcx>> {
     // We do not normalize just any data.  Only scalar layout and slices.
-    let normalize = may_normalize
-        && match op.layout.abi {
-            layout::Abi::Scalar(..) => true,
-            layout::Abi::ScalarPair(..) => op.layout.ty.is_slice(),
-            _ => false,
-        };
+    let normalize = match op.layout.abi {
+        layout::Abi::Scalar(..) => true,
+        layout::Abi::ScalarPair(..) => op.layout.ty.is_slice(),
+        _ => false,
+    };
     let normalized_op = if normalize {
-        ecx.try_read_immediate(op)?
+        Err(*ecx.read_immediate(op).expect("normalization works on validated constants"))
     } else {
-        match *op {
-            Operand::Indirect(mplace) => Err(mplace),
-            Operand::Immediate(val) => Ok(val)
-        }
+        op.try_as_mplace()
     };
     let val = match normalized_op {
-        Err(MemPlace { ptr, align, meta }) => {
-            // extract alloc-offset pair
-            assert!(meta.is_none());
-            let ptr = ptr.to_ptr()?;
-            let alloc = ecx.memory.get(ptr.alloc_id)?;
-            assert!(alloc.align >= align);
-            assert!(alloc.bytes.len() as u64 - ptr.offset.bytes() >= op.layout.size.bytes());
-            let mut alloc = alloc.clone();
-            alloc.align = align;
-            // FIXME shouldn't it be the case that `mark_static_initialized` has already
-            // interned this?  I thought that is the entire point of that `FinishStatic` stuff?
-            let alloc = ecx.tcx.intern_const_alloc(alloc);
-            ConstValue::ByRef(ptr.alloc_id, alloc, ptr.offset)
-        },
-        Ok(Immediate::Scalar(x)) =>
+        Ok(mplace) => return mplace_to_const(ecx, mplace),
+        Err(Immediate::Scalar(x)) =>
             ConstValue::Scalar(x.not_undef()?),
-        Ok(Immediate::ScalarPair(a, b)) =>
+        Err(Immediate::ScalarPair(a, b)) =>
             ConstValue::Slice(a.not_undef()?, b.to_usize(ecx)?),
     };
     Ok(ty::Const { val, ty: op.layout.ty })
@@ -476,7 +477,7 @@ pub fn const_field<'a, 'tcx>(
     let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
     let result = (|| {
         // get the operand again
-        let op = ecx.lazy_const_to_op(ty::LazyConst::Evaluated(value), value.ty)?;
+        let op = ecx.const_to_op(value, None)?;
         // downcast
         let down = match variant {
             None => op,
@@ -486,7 +487,7 @@ pub fn const_field<'a, 'tcx>(
         let field = ecx.operand_field(down, field.index() as u64)?;
         // and finally move back to the const world, always normalizing because
         // this is not called for statics.
-        op_to_const(&ecx, field, true)
+        op_to_const(&ecx, field)
     })();
     result.map_err(|error| {
         let err = error_to_const_error(&ecx, error);
@@ -502,7 +503,7 @@ pub fn const_variant_index<'a, 'tcx>(
 ) -> EvalResult<'tcx, VariantIdx> {
     trace!("const_variant_index: {:?}", val);
     let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env);
-    let op = ecx.lazy_const_to_op(ty::LazyConst::Evaluated(val), val.ty)?;
+    let op = ecx.const_to_op(val, None)?;
     Ok(ecx.read_discriminant(op)?.1)
 }
 
@@ -523,22 +524,23 @@ fn validate_and_turn_into_const<'a, 'tcx>(
     let cid = key.value;
     let ecx = mk_eval_cx(tcx, tcx.def_span(key.value.instance.def_id()), key.param_env);
     let val = (|| {
-        let op = ecx.raw_const_to_mplace(constant)?.into();
-        // FIXME: Once the visitor infrastructure landed, change validation to
-        // work directly on `MPlaceTy`.
-        let mut ref_tracking = RefTracking::new(op);
-        while let Some((op, path)) = ref_tracking.todo.pop() {
+        let mplace = ecx.raw_const_to_mplace(constant)?;
+        let mut ref_tracking = RefTracking::new(mplace);
+        while let Some((mplace, path)) = ref_tracking.todo.pop() {
             ecx.validate_operand(
-                op,
+                mplace.into(),
                 path,
                 Some(&mut ref_tracking),
                 true, // const mode
             )?;
         }
         // Now that we validated, turn this into a proper constant.
         let def_id = cid.instance.def.def_id();
-        let normalize = tcx.is_static(def_id).is_none() && cid.promoted.is_none();
-        op_to_const(&ecx, op, normalize)
+        if tcx.is_static(def_id).is_some() || cid.promoted.is_some() {
+            mplace_to_const(&ecx, mplace)
+        } else {
+            op_to_const(&ecx, mplace.into())
+        }
     })();
 
     val.map_err(|error| {

src/librustc_mir/hair/pattern/_match.rs

@@ -172,7 +172,7 @@ use rustc::ty::{self, Ty, TyCtxt, TypeFoldable, Const};
 use rustc::ty::layout::{Integer, IntegerExt, VariantIdx, Size};
 
 use rustc::mir::Field;
-use rustc::mir::interpret::{ConstValue, Pointer, Scalar};
+use rustc::mir::interpret::{ConstValue, Scalar};
 use rustc::util::common::ErrorReported;
 
 use syntax::attr::{SignedInt, UnsignedInt};
@@ -214,9 +214,8 @@ impl<'a, 'tcx> LiteralExpander<'a, 'tcx> {
         match (val, &crty.sty, &rty.sty) {
             // the easy case, deref a reference
             (ConstValue::Scalar(Scalar::Ptr(p)), x, y) if x == y => ConstValue::ByRef(
-                p.alloc_id,
+                p,
                 self.tcx.alloc_map.lock().unwrap_memory(p.alloc_id),
-                p.offset,
             ),
             // unsize array to slice if pattern is array but match value or other patterns are slice
             (ConstValue::Scalar(Scalar::Ptr(p)), ty::Array(t, n), ty::Slice(u)) => {
@@ -1428,15 +1427,14 @@ 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(id, alloc, offset), ty::Array(t, n)) => {
+        (ConstValue::ByRef(ptr, alloc), ty::Array(t, n)) => {
             if *t != tcx.types.u8 {
                 // FIXME(oli-obk): can't mix const patterns with slice patterns and get
                 // any sort of exhaustiveness/unreachable check yet
                 // This solely means that we don't lint about unreachable patterns, even if some
                 // are definitely unreachable.
                 return Ok(false);
             }
-            let ptr = Pointer::new(id, offset);
             let n = n.assert_usize(tcx).unwrap();
             alloc.get_bytes(&tcx, ptr, Size::from_bytes(n)).unwrap()
         },
@@ -1778,8 +1776,8 @@ fn specialize<'p, 'a: 'p, 'tcx: 'a>(
                     let (opt_ptr, n, ty) = match value.ty.sty {
                         ty::TyKind::Array(t, n) => {
                             match value.val {
-                                ConstValue::ByRef(id, alloc, offset) => (
-                                    Some((Pointer::new(id, offset), alloc)),
+                                ConstValue::ByRef(ptr, alloc) => (
+                                    Some((ptr, alloc)),
                                     n.unwrap_usize(cx.tcx),
                                     t,
                                 ),