compiler: spring cleaning

I started this diff trying to remove a little dead code from the C
backend, but ended up finding a bunch of dead code sprinkled all over
the place:

* `packed` handling in the C backend which was made dead by `Legalize`
* Representation of pointers to runtime-known vector indices
* Handling for the `vector_store_elem` AIR instruction (now removed)
* Old tuple handling from when they used the InternPool repr of structs
* Straightforward unused functions
* TODOs in the LLVM backend for features which Zig just does not support

Author: mlugg

src/Air.zig

@@ -874,10 +874,6 @@ pub const Inst = struct {
         /// Uses the `ty_pl` field.
         save_err_return_trace_index,
 
-        /// Store an element to a vector pointer at an index.
-        /// Uses the `vector_store_elem` field.
-        vector_store_elem,
-
         /// Compute a pointer to a `Nav` at runtime, always one of:
         ///
         /// * `threadlocal var`
@@ -1220,11 +1216,6 @@ pub const Inst = struct {
             operand: Ref,
             operation: std.builtin.ReduceOp,
         },
-        vector_store_elem: struct {
-            vector_ptr: Ref,
-            // Index into a different array.
-            payload: u32,
-        },
         ty_nav: struct {
             ty: InternPool.Index,
             nav: InternPool.Nav.Index,
@@ -1689,7 +1680,6 @@ pub fn typeOfIndex(air: *const Air, inst: Air.Inst.Index, ip: *const InternPool)
         .set_union_tag,
         .prefetch,
         .set_err_return_trace,
-        .vector_store_elem,
         .c_va_end,
         => return .void,
 
@@ -1857,7 +1847,6 @@ pub fn mustLower(air: Air, inst: Air.Inst.Index, ip: *const InternPool) bool {
         .prefetch,
         .wasm_memory_grow,
         .set_err_return_trace,
-        .vector_store_elem,
         .c_va_arg,
         .c_va_copy,
         .c_va_end,

src/Air/Liveness.zig

@@ -463,12 +463,6 @@ fn analyzeInst(
             return analyzeOperands(a, pass, data, inst, .{ o.lhs, o.rhs, .none });
         },
 
-        .vector_store_elem => {
-            const o = inst_datas[@intFromEnum(inst)].vector_store_elem;
-            const extra = a.air.extraData(Air.Bin, o.payload).data;
-            return analyzeOperands(a, pass, data, inst, .{ o.vector_ptr, extra.lhs, extra.rhs });
-        },
-
         .arg,
         .alloc,
         .ret_ptr,

src/Air/Liveness/Verify.zig

@@ -322,11 +322,6 @@ fn verifyBody(self: *Verify, body: []const Air.Inst.Index) Error!void {
                 const extra = self.air.extraData(Air.Bin, pl_op.payload).data;
                 try self.verifyInstOperands(inst, .{ extra.lhs, extra.rhs, pl_op.operand });
             },
-            .vector_store_elem => {
-                const vector_store_elem = data[@intFromEnum(inst)].vector_store_elem;
-                const extra = self.air.extraData(Air.Bin, vector_store_elem.payload).data;
-                try self.verifyInstOperands(inst, .{ vector_store_elem.vector_ptr, extra.lhs, extra.rhs });
-            },
             .cmpxchg_strong,
             .cmpxchg_weak,
             => {

src/Air/print.zig

@@ -330,7 +330,6 @@ const Writer = struct {
             .shuffle_two => try w.writeShuffleTwo(s, inst),
             .reduce, .reduce_optimized => try w.writeReduce(s, inst),
             .cmp_vector, .cmp_vector_optimized => try w.writeCmpVector(s, inst),
-            .vector_store_elem => try w.writeVectorStoreElem(s, inst),
             .runtime_nav_ptr => try w.writeRuntimeNavPtr(s, inst),
 
             .work_item_id,
@@ -576,17 +575,6 @@ const Writer = struct {
         try w.writeOperand(s, inst, 1, extra.rhs);
     }
 
-    fn writeVectorStoreElem(w: *Writer, s: *std.Io.Writer, inst: Air.Inst.Index) Error!void {
-        const data = w.air.instructions.items(.data)[@intFromEnum(inst)].vector_store_elem;
-        const extra = w.air.extraData(Air.VectorCmp, data.payload).data;
-
-        try w.writeOperand(s, inst, 0, data.vector_ptr);
-        try s.writeAll(", ");
-        try w.writeOperand(s, inst, 1, extra.lhs);
-        try s.writeAll(", ");
-        try w.writeOperand(s, inst, 2, extra.rhs);
-    }
-
     fn writeRuntimeNavPtr(w: *Writer, s: *std.Io.Writer, inst: Air.Inst.Index) Error!void {
         const ip = &w.pt.zcu.intern_pool;
         const ty_nav = w.air.instructions.items(.data)[@intFromEnum(inst)].ty_nav;

src/Air/types_resolved.zig

@@ -316,13 +316,6 @@ fn checkBody(air: Air, body: []const Air.Inst.Index, zcu: *Zcu) bool {
                 if (!checkRef(data.prefetch.ptr, zcu)) return false;
             },
 
-            .vector_store_elem => {
-                const bin = air.extraData(Air.Bin, data.vector_store_elem.payload).data;
-                if (!checkRef(data.vector_store_elem.vector_ptr, zcu)) return false;
-                if (!checkRef(bin.lhs, zcu)) return false;
-                if (!checkRef(bin.rhs, zcu)) return false;
-            },
-
             .runtime_nav_ptr => {
                 if (!checkType(.fromInterned(data.ty_nav.ty), zcu)) return false;
             },

src/InternPool.zig

@@ -2104,7 +2104,6 @@ pub const Key = union(enum) {
 
         pub const VectorIndex = enum(u16) {
             none = std.math.maxInt(u16),
-            runtime = std.math.maxInt(u16) - 1,
             _,
         };
 
@@ -3739,10 +3738,8 @@ pub const LoadedStructType = struct {
         return s.field_inits.get(ip)[i];
     }
 
-    /// Returns `none` in the case the struct is a tuple.
-    pub fn fieldName(s: LoadedStructType, ip: *const InternPool, i: usize) OptionalNullTerminatedString {
-        if (s.field_names.len == 0) return .none;
-        return s.field_names.get(ip)[i].toOptional();
+    pub fn fieldName(s: LoadedStructType, ip: *const InternPool, i: usize) NullTerminatedString {
+        return s.field_names.get(ip)[i];
     }
 
     pub fn fieldIsComptime(s: LoadedStructType, ip: *const InternPool, i: usize) bool {

src/Sema.zig

@@ -17732,10 +17732,7 @@ fn zirTypeInfo(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError!Ai
                 try ty.resolveStructFieldInits(pt);
 
                 for (struct_field_vals, 0..) |*field_val, field_index| {
-                    const field_name = if (struct_type.fieldName(ip, field_index).unwrap()) |field_name|
-                        field_name
-                    else
-                        try ip.getOrPutStringFmt(gpa, pt.tid, "{d}", .{field_index}, .no_embedded_nulls);
+                    const field_name = struct_type.fieldName(ip, field_index);
                     const field_name_len = field_name.length(ip);
                     const field_ty: Type = .fromInterned(struct_type.field_types.get(ip)[field_index]);
                     const field_init = struct_type.fieldInit(ip, field_index);
@@ -28334,6 +28331,10 @@ fn elemPtrArray(
         break :o index;
     } else null;
 
+    if (offset == null and array_ty.zigTypeTag(zcu) == .vector) {
+        return sema.fail(block, elem_index_src, "vector index not comptime known", .{});
+    }
+
     const elem_ptr_ty = try array_ptr_ty.elemPtrType(offset, pt);
 
     if (maybe_undef_array_ptr_val) |array_ptr_val| {
@@ -28351,10 +28352,6 @@ fn elemPtrArray(
         try sema.validateRuntimeValue(block, array_ptr_src, array_ptr);
     }
 
-    if (offset == null and array_ty.zigTypeTag(zcu) == .vector) {
-        return sema.fail(block, elem_index_src, "vector index not comptime known", .{});
-    }
-
     // Runtime check is only needed if unable to comptime check.
     if (oob_safety and block.wantSafety() and offset == null) {
         const len_inst = try pt.intRef(.usize, array_len);
@@ -30386,22 +30383,6 @@ fn storePtr2(
 
     const is_ret = air_tag == .ret_ptr;
 
-    // Detect if we are storing an array operand to a bitcasted vector pointer.
-    // If so, we instead reach through the bitcasted pointer to the vector pointer,
-    // bitcast the array operand to a vector, and then lower this as a store of
-    // a vector value to a vector pointer. This generally results in better code,
-    // as well as working around an LLVM bug:
-    // https://github.com/ziglang/zig/issues/11154
-    if (sema.obtainBitCastedVectorPtr(ptr)) |vector_ptr| {
-        const vector_ty = sema.typeOf(vector_ptr).childType(zcu);
-        const vector = sema.coerceExtra(block, vector_ty, uncasted_operand, operand_src, .{ .is_ret = is_ret }) catch |err| switch (err) {
-            error.NotCoercible => unreachable,
-            else => |e| return e,
-        };
-        try sema.storePtr2(block, src, vector_ptr, ptr_src, vector, operand_src, .store);
-        return;
-    }
-
     const operand = sema.coerceExtra(block, elem_ty, uncasted_operand, operand_src, .{ .is_ret = is_ret }) catch |err| switch (err) {
         error.NotCoercible => unreachable,
         else => |e| return e,
@@ -30434,29 +30415,6 @@ fn storePtr2(
 
     try sema.requireRuntimeBlock(block, src, runtime_src);
 
-    if (ptr_ty.ptrInfo(zcu).flags.vector_index == .runtime) {
-        const ptr_inst = ptr.toIndex().?;
-        const air_tags = sema.air_instructions.items(.tag);
-        if (air_tags[@intFromEnum(ptr_inst)] == .ptr_elem_ptr) {
-            const ty_pl = sema.air_instructions.items(.data)[@intFromEnum(ptr_inst)].ty_pl;
-            const bin_op = sema.getTmpAir().extraData(Air.Bin, ty_pl.payload).data;
-            _ = try block.addInst(.{
-                .tag = .vector_store_elem,
-                .data = .{ .vector_store_elem = .{
-                    .vector_ptr = bin_op.lhs,
-                    .payload = try block.sema.addExtra(Air.Bin{
-                        .lhs = bin_op.rhs,
-                        .rhs = operand,
-                    }),
-                } },
-            });
-            return;
-        }
-        return sema.fail(block, ptr_src, "unable to determine vector element index of type '{f}'", .{
-            ptr_ty.fmt(pt),
-        });
-    }
-
     const store_inst = if (is_ret)
         try block.addBinOp(.store, ptr, operand)
     else
@@ -30556,37 +30514,6 @@ fn markMaybeComptimeAllocRuntime(sema: *Sema, block: *Block, alloc_inst: Air.Ins
     }
 }
 
-/// Traverse an arbitrary number of bitcasted pointers and return the underyling vector
-/// pointer. Only if the final element type matches the vector element type, and the
-/// lengths match.
-fn obtainBitCastedVectorPtr(sema: *Sema, ptr: Air.Inst.Ref) ?Air.Inst.Ref {
-    const pt = sema.pt;
-    const zcu = pt.zcu;
-    const array_ty = sema.typeOf(ptr).childType(zcu);
-    if (array_ty.zigTypeTag(zcu) != .array) return null;
-    var ptr_ref = ptr;
-    var ptr_inst = ptr_ref.toIndex() orelse return null;
-    const air_datas = sema.air_instructions.items(.data);
-    const air_tags = sema.air_instructions.items(.tag);
-    const vector_ty = while (air_tags[@intFromEnum(ptr_inst)] == .bitcast) {
-        ptr_ref = air_datas[@intFromEnum(ptr_inst)].ty_op.operand;
-        if (!sema.isKnownZigType(ptr_ref, .pointer)) return null;
-        const child_ty = sema.typeOf(ptr_ref).childType(zcu);
-        if (child_ty.zigTypeTag(zcu) == .vector) break child_ty;
-        ptr_inst = ptr_ref.toIndex() orelse return null;
-    } else return null;
-
-    // We have a pointer-to-array and a pointer-to-vector. If the elements and
-    // lengths match, return the result.
-    if (array_ty.childType(zcu).eql(vector_ty.childType(zcu), zcu) and
-        array_ty.arrayLen(zcu) == vector_ty.vectorLen(zcu))
-    {
-        return ptr_ref;
-    } else {
-        return null;
-    }
-}
-
 /// Call when you have Value objects rather than Air instructions, and you want to
 /// assert the store must be done at comptime.
 fn storePtrVal(
@@ -35566,8 +35493,13 @@ fn structFieldInits(
             const default_val = try sema.resolveConstValue(&block_scope, init_src, coerced, null);
 
             if (default_val.canMutateComptimeVarState(zcu)) {
-                const field_name = struct_type.fieldName(ip, field_i).unwrap().?;
-                return sema.failWithContainsReferenceToComptimeVar(&block_scope, init_src, field_name, "field default value", default_val);
+                return sema.failWithContainsReferenceToComptimeVar(
+                    &block_scope,
+                    init_src,
+                    struct_type.fieldName(ip, field_i),
+                    "field default value",
+                    default_val,
+                );
             }
             struct_type.field_inits.get(ip)[field_i] = default_val.toIntern();
         }

src/Sema/comptime_ptr_access.zig

@@ -24,7 +24,6 @@ pub fn loadComptimePtr(sema: *Sema, block: *Block, src: LazySrcLoc, ptr: Value)
         const child_bits = Type.fromInterned(ptr_info.child).bitSize(zcu);
         const bit_offset = ptr_info.packed_offset.bit_offset + switch (ptr_info.flags.vector_index) {
             .none => 0,
-            .runtime => return .runtime_load,
             else => |idx| switch (pt.zcu.getTarget().cpu.arch.endian()) {
                 .little => child_bits * @intFromEnum(idx),
                 .big => host_bits - child_bits * (@intFromEnum(idx) + 1), // element order reversed on big endian
@@ -81,7 +80,6 @@ pub fn storeComptimePtr(
     };
     const bit_offset = ptr_info.packed_offset.bit_offset + switch (ptr_info.flags.vector_index) {
         .none => 0,
-        .runtime => return .runtime_store,
         else => |idx| switch (zcu.getTarget().cpu.arch.endian()) {
             .little => Type.fromInterned(ptr_info.child).bitSize(zcu) * @intFromEnum(idx),
             .big => host_bits - Type.fromInterned(ptr_info.child).bitSize(zcu) * (@intFromEnum(idx) + 1), // element order reversed on big endian

src/Type.zig

@@ -198,9 +198,7 @@ pub fn print(ty: Type, writer: *std.Io.Writer, pt: Zcu.PerThread) std.Io.Writer.
                         info.packed_offset.bit_offset, info.packed_offset.host_size,
                     });
                 }
-                if (info.flags.vector_index == .runtime) {
-                    try writer.writeAll(":?");
-                } else if (info.flags.vector_index != .none) {
+                if (info.flags.vector_index != .none) {
                     try writer.print(":{d}", .{@intFromEnum(info.flags.vector_index)});
                 }
                 try writer.writeAll(") ");
@@ -3113,7 +3111,7 @@ pub fn enumTagFieldIndex(ty: Type, enum_tag: Value, zcu: *const Zcu) ?u32 {
 pub fn structFieldName(ty: Type, index: usize, zcu: *const Zcu) InternPool.OptionalNullTerminatedString {
     const ip = &zcu.intern_pool;
     return switch (ip.indexToKey(ty.toIntern())) {
-        .struct_type => ip.loadStructType(ty.toIntern()).fieldName(ip, index),
+        .struct_type => ip.loadStructType(ty.toIntern()).fieldName(ip, index).toOptional(),
         .tuple_type => .none,
         else => unreachable,
     };
@@ -3985,7 +3983,7 @@ pub fn elemPtrType(ptr_ty: Type, offset: ?usize, pt: Zcu.PerThread) !Type {
         break :blk .{
             .host_size = @intCast(parent_ty.arrayLen(zcu)),
             .alignment = parent_ty.abiAlignment(zcu),
-            .vector_index = if (offset) |some| @enumFromInt(some) else .runtime,
+            .vector_index = @enumFromInt(offset.?),
         };
     } else .{};