handle from_start range case

Author: xacrimon

compiler/rustc_mir_build/src/builder/matches/test.rs

@@ -20,6 +20,7 @@ use rustc_span::{DUMMY_SP, Span, Symbol, sym};
 use rustc_trait_selection::infer::InferCtxtExt;
 use tracing::{debug, instrument};
 
+use crate::builder::matches::util::Range;
 use crate::builder::matches::{Candidate, MatchPairTree, Test, TestBranch, TestCase, TestKind};
 use crate::builder::{Builder, PlaceBuilder};
 
@@ -182,8 +183,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     );
                 } else if !ty.is_scalar() {
                     let (place, block) = if let Some(range) = range {
-                        // TODO: range handling
-                        assert_eq!(range.start, 0);
                         let target_block = self.cfg.start_new_block();
                         let subslice = self.subslice(
                             block,
@@ -192,7 +191,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                             place_ty.ty,
                             test.span,
                             ty.sequence_element_type(tcx),
-                            range.end,
+                            range,
                         );
 
                         (subslice, target_block)
@@ -319,11 +318,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         input_ty: Ty<'tcx>,
         span: Span,
         elem_ty: Ty<'tcx>,
-        new_len: u64,
+        range: Range,
     ) -> Place<'tcx> {
         let tcx = self.tcx;
         let source_info = self.source_info(span);
 
+        // TODO: handle range.from_end == true
+
         let temp_source_ptr = self.temp(Ty::new_ptr(tcx, input_ty, Mutability::Not), span);
         self.cfg.push_assign(
             block,
@@ -335,15 +336,31 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         let elem_ptr_ty = Ty::new_ptr(tcx, elem_ty, Mutability::Not);
         let slice_ptr_ty = Ty::new_ptr(tcx, Ty::new_slice(tcx, elem_ty), Mutability::Not);
 
-        let temp_elem_ptr = self.temp(elem_ptr_ty, span);
+        let mut temp_elem_ptr = self.temp(elem_ptr_ty, span);
         self.cfg.push_assign(
             block,
             source_info,
             temp_elem_ptr,
             Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(temp_source_ptr), elem_ptr_ty),
         );
 
-        let temp_len = self.push_usize(block, source_info, new_len);
+        if range.start != 0 {
+            let offset = self.temp(elem_ptr_ty, span);
+            let offset_by = self.push_usize(block, source_info, range.start);
+            self.cfg.push_assign(
+                block,
+                source_info,
+                offset,
+                Rvalue::BinaryOp(
+                    BinOp::Offset,
+                    Box::new((Operand::Copy(temp_elem_ptr), Operand::Move(offset_by))),
+                ),
+            );
+
+            temp_elem_ptr = offset;
+        }
+
+        let temp_len = self.push_usize(block, source_info, range.len());
 
         let aggregate_raw_ptr = Operand::function_handle(
             tcx,

compiler/rustc_mir_build/src/builder/matches/util.rs

@@ -249,6 +249,6 @@ impl Range {
     }
 
     pub(crate) fn len(&self) -> u64 {
-        todo!()
+        if !self.from_end { self.end - self.start } else { self.start - self.end }
     }
 }