Support ConstantIndex in debuginfo.

Author: cjgillot

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -8,7 +8,7 @@ use rustc_middle::ty::layout::{HasTyCtxt, LayoutOf};
 use rustc_session::config::DebugInfo;
 use rustc_span::symbol::{kw, Symbol};
 use rustc_span::{BytePos, Span};
-use rustc_target::abi::{Abi, FieldIdx, Size, VariantIdx};
+use rustc_target::abi::{Abi, FieldIdx, FieldsShape, Size, VariantIdx};
 
 use super::operand::{OperandRef, OperandValue};
 use super::place::PlaceRef;
@@ -83,6 +83,7 @@ trait DebugInfoOffsetLocation<'tcx, Bx> {
     fn deref(&self, bx: &mut Bx) -> Self;
     fn layout(&self) -> TyAndLayout<'tcx>;
     fn project_field(&self, bx: &mut Bx, field: FieldIdx) -> Self;
+    fn project_constant_index(&self, bx: &mut Bx, offset: u64) -> Self;
     fn downcast(&self, bx: &mut Bx, variant: VariantIdx) -> Self;
 }
 
@@ -101,6 +102,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> DebugInfoOffsetLocation<'tcx, Bx>
         PlaceRef::project_field(*self, bx, field.index())
     }
 
+    fn project_constant_index(&self, bx: &mut Bx, offset: u64) -> Self {
+        let lloffset = bx.cx().const_usize(offset);
+        self.project_index(bx, lloffset)
+    }
+
     fn downcast(&self, bx: &mut Bx, variant: VariantIdx) -> Self {
         self.project_downcast(bx, variant)
     }
@@ -123,6 +129,10 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> DebugInfoOffsetLocation<'tcx, Bx>
         self.field(bx.cx(), field.index())
     }
 
+    fn project_constant_index(&self, bx: &mut Bx, index: u64) -> Self {
+        self.field(bx.cx(), index as usize)
+    }
+
     fn downcast(&self, bx: &mut Bx, variant: VariantIdx) -> Self {
         self.for_variant(bx.cx(), variant)
     }
@@ -168,6 +178,18 @@ fn calculate_debuginfo_offset<
             mir::ProjectionElem::Downcast(_, variant) => {
                 place = place.downcast(bx, variant);
             }
+            mir::ProjectionElem::ConstantIndex {
+                offset: index,
+                min_length: _,
+                from_end: false,
+            } => {
+                let offset = indirect_offsets.last_mut().unwrap_or(&mut direct_offset);
+                let FieldsShape::Array { stride, count: _ } = place.layout().fields else {
+                    span_bug!(var.source_info.span, "ConstantIndex on non-array type {:?}", place.layout())
+                };
+                *offset += stride * index;
+                place = place.project_constant_index(bx, index);
+            }
             _ => {
                 // Sanity check for `can_use_in_debuginfo`.
                 debug_assert!(!elem.can_use_in_debuginfo());

compiler/rustc_middle/src/mir/mod.rs

@@ -1554,8 +1554,11 @@ impl<V, T> ProjectionElem<V, T> {
     /// Returns `true` if this is accepted inside `VarDebugInfoContents::Place`.
     pub fn can_use_in_debuginfo(&self) -> bool {
         match self {
-            Self::Deref | Self::Downcast(_, _) | Self::Field(_, _) => true,
-            Self::ConstantIndex { .. }
+            Self::ConstantIndex { from_end: false, .. }
+            | Self::Deref
+            | Self::Downcast(_, _)
+            | Self::Field(_, _) => true,
+            Self::ConstantIndex { from_end: true, .. }
             | Self::Index(_)
             | Self::OpaqueCast(_)
             | Self::Subslice { .. } => false,

tests/mir-opt/issue_76432.test.SimplifyComparisonIntegral.diff

@@ -21,9 +21,9 @@
           let _13: &T;                     // in scope 1 at $DIR/issue_76432.rs:+3:18: +3:24
           let _14: &T;                     // in scope 1 at $DIR/issue_76432.rs:+3:26: +3:32
           scope 2 {
-              debug v1 => _12;             // in scope 2 at $DIR/issue_76432.rs:+3:10: +3:16
-              debug v2 => _13;             // in scope 2 at $DIR/issue_76432.rs:+3:18: +3:24
-              debug v3 => _14;             // in scope 2 at $DIR/issue_76432.rs:+3:26: +3:32
+              debug v1 => &(*_2)[0 of 3];  // in scope 2 at $DIR/issue_76432.rs:+3:10: +3:16
+              debug v2 => &(*_2)[1 of 3];  // in scope 2 at $DIR/issue_76432.rs:+3:18: +3:24
+              debug v3 => &(*_2)[2 of 3];  // in scope 2 at $DIR/issue_76432.rs:+3:26: +3:32
           }
       }
 
@@ -52,15 +52,6 @@
       }
 
       bb2: {
-          StorageLive(_12);                // scope 1 at $DIR/issue_76432.rs:+3:10: +3:16
-          _12 = &(*_2)[0 of 3];            // scope 1 at $DIR/issue_76432.rs:+3:10: +3:16
-          StorageLive(_13);                // scope 1 at $DIR/issue_76432.rs:+3:18: +3:24
-          _13 = &(*_2)[1 of 3];            // scope 1 at $DIR/issue_76432.rs:+3:18: +3:24
-          StorageLive(_14);                // scope 1 at $DIR/issue_76432.rs:+3:26: +3:32
-          _14 = &(*_2)[2 of 3];            // scope 1 at $DIR/issue_76432.rs:+3:26: +3:32
-          StorageDead(_14);                // scope 1 at $DIR/issue_76432.rs:+3:84: +3:85
-          StorageDead(_13);                // scope 1 at $DIR/issue_76432.rs:+3:84: +3:85
-          StorageDead(_12);                // scope 1 at $DIR/issue_76432.rs:+3:84: +3:85
           StorageDead(_5);                 // scope 0 at $DIR/issue_76432.rs:+6:1: +6:2
           StorageDead(_2);                 // scope 0 at $DIR/issue_76432.rs:+6:1: +6:2
           return;                          // scope 0 at $DIR/issue_76432.rs:+6:2: +6:2