Sema: detect one-possible-value types after function calls

produces better Air for backends

Author: andrewrk

src/Air.zig

@@ -1141,6 +1141,20 @@ pub const Inst = struct {
         pub fn toType(ref: Ref) Type {
             return .fromInterned(ref.toInterned().?);
         }
+
+        pub fn fromIntern(ip_index: InternPool.Index) Ref {
+            return switch (ip_index) {
+                .none => .none,
+                else => {
+                    assert(@intFromEnum(ip_index) >> 31 == 0);
+                    return @enumFromInt(@as(u31, @intCast(@intFromEnum(ip_index))));
+                },
+            };
+        }
+
+        pub fn fromValue(v: Value) Ref {
+            return .fromIntern(v.toIntern());
+        }
     };
 
     /// All instructions have an 8-byte payload, which is contained within
@@ -1754,13 +1768,7 @@ pub fn deinit(air: *Air, gpa: std.mem.Allocator) void {
 }
 
 pub fn internedToRef(ip_index: InternPool.Index) Inst.Ref {
-    return switch (ip_index) {
-        .none => .none,
-        else => {
-            assert(@intFromEnum(ip_index) >> 31 == 0);
-            return @enumFromInt(@as(u31, @intCast(@intFromEnum(ip_index))));
-        },
-    };
+    return .fromIntern(ip_index);
 }
 
 /// Returns `null` if runtime-known.

src/Sema.zig

@@ -8060,7 +8060,7 @@ fn analyzeCall(
         };
 
         try sema.air_extra.ensureUnusedCapacity(gpa, @typeInfo(Air.Call).@"struct".fields.len + runtime_args.len);
-        const result = try block.addInst(.{
+        const maybe_opv = try block.addInst(.{
             .tag = call_tag,
             .data = .{ .pl_op = .{
                 .operand = runtime_func,
@@ -8072,7 +8072,7 @@ fn analyzeCall(
         sema.appendRefsAssumeCapacity(runtime_args);
 
         if (ensure_result_used) {
-            try sema.ensureResultUsed(block, sema.typeOf(result), call_src);
+            try sema.ensureResultUsed(block, sema.typeOf(maybe_opv), call_src);
         }
 
         if (call_tag == .call_always_tail) {
@@ -8082,10 +8082,10 @@ fn analyzeCall(
                 .pointer => func_or_ptr_ty.childType(zcu),
                 else => unreachable,
             };
-            return sema.handleTailCall(block, call_src, runtime_func_ty, result);
+            return sema.handleTailCall(block, call_src, runtime_func_ty, maybe_opv);
         }
 
-        if (resolved_ret_ty.toIntern() == .noreturn_type) {
+        if (ip.isNoReturn(resolved_ret_ty.toIntern())) {
             const want_check = c: {
                 if (!block.wantSafety()) break :c false;
                 if (func_val != null) break :c false;
@@ -8099,6 +8099,11 @@ fn analyzeCall(
             return .unreachable_value;
         }
 
+        const result: Air.Inst.Ref = if (try sema.typeHasOnePossibleValue(sema.typeOf(maybe_opv))) |opv|
+            .fromValue(opv)
+        else
+            maybe_opv;
+
         return result;
     }
 
@@ -8335,7 +8340,7 @@ fn analyzeCall(
         break :result try sema.resolveAnalyzedBlock(block, call_src, &child_block, &inlining.merges, need_debug_scope);
     };
 
-    const result: Air.Inst.Ref = if (try sema.resolveValue(result_raw)) |result_val| r: {
+    const maybe_opv: Air.Inst.Ref = if (try sema.resolveValue(result_raw)) |result_val| r: {
         const val_resolved = try sema.resolveAdHocInferredErrorSet(block, call_src, result_val.toIntern());
         break :r Air.internedToRef(val_resolved);
     } else r: {
@@ -8347,7 +8352,7 @@ fn analyzeCall(
     };
 
     if (block.isComptime()) {
-        const result_val = (try sema.resolveValue(result)).?;
+        const result_val = (try sema.resolveValue(maybe_opv)).?;
         if (want_memoize and sema.allow_memoize and !result_val.canMutateComptimeVarState(zcu)) {
             _ = try pt.intern(.{ .memoized_call = .{
                 .func = func_val.?.toIntern(),
@@ -8359,10 +8364,10 @@ fn analyzeCall(
     }
 
     if (ensure_result_used) {
-        try sema.ensureResultUsed(block, sema.typeOf(result), call_src);
+        try sema.ensureResultUsed(block, sema.typeOf(maybe_opv), call_src);
     }
 
-    return result;
+    return maybe_opv;
 }
 
 fn handleTailCall(sema: *Sema, block: *Block, call_src: LazySrcLoc, func_ty: Type, result: Air.Inst.Ref) !Air.Inst.Ref {