Make alignment checks a future incompat lint

compiler/rustc_const_eval/src/interpret/memory.rs

@@ -14,10 +14,15 @@ use std::ptr;
 
 use rustc_ast::Mutability;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_hir::CRATE_HIR_ID;
 use rustc_middle::mir::display_allocation;
+use rustc_middle::mir::interpret::UndefinedBehaviorInfo;
 use rustc_middle::ty::{self, Instance, ParamEnv, Ty, TyCtxt};
+use rustc_session::lint::builtin::INVALID_ALIGNMENT;
 use rustc_target::abi::{Align, HasDataLayout, Size};
 
+use crate::const_eval::CheckAlignment;
+
 use super::{
     alloc_range, AllocId, AllocMap, AllocRange, Allocation, CheckInAllocMsg, GlobalAlloc, InterpCx,
     InterpResult, Machine, MayLeak, Pointer, PointerArithmetic, Provenance, Scalar,
@@ -377,7 +382,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             ptr,
             size,
             align,
-            /* force_alignment_check */ true,
+            CheckAlignment::Error,
             msg,
             |alloc_id, _, _| {
                 let (size, align) = self.get_live_alloc_size_and_align(alloc_id)?;
@@ -396,7 +401,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         ptr: Pointer<Option<M::Provenance>>,
         size: Size,
         align: Align,
-        force_alignment_check: bool,
+        check: CheckAlignment,
         msg: CheckInAllocMsg,
         alloc_size: impl FnOnce(
             AllocId,
@@ -404,19 +409,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             M::ProvenanceExtra,
         ) -> InterpResult<'tcx, (Size, Align, T)>,
     ) -> InterpResult<'tcx, Option<T>> {
-        fn check_offset_align<'tcx>(offset: u64, align: Align) -> InterpResult<'tcx> {
-            if offset % align.bytes() == 0 {
-                Ok(())
-            } else {
-                // The biggest power of two through which `offset` is divisible.
-                let offset_pow2 = 1 << offset.trailing_zeros();
-                throw_ub!(AlignmentCheckFailed {
-                    has: Align::from_bytes(offset_pow2).unwrap(),
-                    required: align,
-                })
-            }
-        }
-
         Ok(match self.ptr_try_get_alloc_id(ptr) {
             Err(addr) => {
                 // We couldn't get a proper allocation. This is only okay if the access size is 0,
@@ -425,8 +417,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     throw_ub!(DanglingIntPointer(addr, msg));
                 }
                 // Must be aligned.
-                if force_alignment_check {
-                    check_offset_align(addr, align)?;
+                if check.should_check() {
+                    self.check_offset_align(addr, align, check)?;
                 }
                 None
             }
@@ -449,16 +441,16 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 }
                 // Test align. Check this last; if both bounds and alignment are violated
                 // we want the error to be about the bounds.
-                if force_alignment_check {
+                if check.should_check() {
                     if M::use_addr_for_alignment_check(self) {
                         // `use_addr_for_alignment_check` can only be true if `OFFSET_IS_ADDR` is true.
-                        check_offset_align(ptr.addr().bytes(), align)?;
+                        self.check_offset_align(ptr.addr().bytes(), align, check)?;
                     } else {
                         // Check allocation alignment and offset alignment.
                         if alloc_align.bytes() < align.bytes() {
-                            throw_ub!(AlignmentCheckFailed { has: alloc_align, required: align });
+                            self.alignment_check_failed(alloc_align, align, check)?;
                         }
-                        check_offset_align(offset.bytes(), align)?;
+                        self.check_offset_align(offset.bytes(), align, check)?;
                     }
                 }
 
@@ -468,6 +460,55 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
         })
     }
+
+    fn check_offset_align(
+        &self,
+        offset: u64,
+        align: Align,
+        check: CheckAlignment,
+    ) -> InterpResult<'tcx> {
+        if offset % align.bytes() == 0 {
+            Ok(())
+        } else {
+            // The biggest power of two through which `offset` is divisible.
+            let offset_pow2 = 1 << offset.trailing_zeros();
+            self.alignment_check_failed(Align::from_bytes(offset_pow2).unwrap(), align, check)
+        }
+    }
+
+    fn alignment_check_failed(
+        &self,
+        has: Align,
+        required: Align,
+        check: CheckAlignment,
+    ) -> InterpResult<'tcx, ()> {
+        match check {
+            CheckAlignment::Error => {
+                throw_ub!(AlignmentCheckFailed { has, required })
+            }
+            CheckAlignment::No => span_bug!(
+                self.cur_span(),
+                "`alignment_check_failed` called when no alignment check requested"
+            ),
+            CheckAlignment::FutureIncompat => self.tcx.struct_span_lint_hir(
+                INVALID_ALIGNMENT,
+                self.stack().iter().find_map(|frame| frame.lint_root()).unwrap_or(CRATE_HIR_ID),
+                self.cur_span(),
+                UndefinedBehaviorInfo::AlignmentCheckFailed { has, required }.to_string(),
+                |db| {
+                    let mut stacktrace = self.generate_stacktrace();
+                    // Filter out `requires_caller_location` frames.
+                    stacktrace
+                        .retain(|frame| !frame.instance.def.requires_caller_location(*self.tcx));
+                    for frame in stacktrace {
+                        db.span_label(frame.span, format!("inside `{}`", frame.instance));
+                    }
+                    db
+                },
+            ),
+        }
+        Ok(())
+    }
 }
 
 /// Allocation accessors