spirv: enhance assembler to handle placeholders and result ID resolution

Author: ivanstepanovftw

lib/std/gpu.zig

@@ -135,10 +135,10 @@ pub fn printf(comptime fmt: [*:0]const u8, args: anytype) u32 {
         comptime var expr: []const u8 =
             \\%std = OpExtInstImport "OpenCL.std"
             \\%u32 = OpTypeInt 32 0
-            \\%ret = OpExtInst %u32 %std 184 %fmt
+            \\%ret = OpExtInst %u32 %std 184 $fmt
         ;
         inline for (0..args.len) |i| {
-            expr = expr ++ std.fmt.comptimePrint(" %arg{d}", .{i});
+            expr = expr ++ std.fmt.comptimePrint(" $arg{d}", .{i});
         }
         const result = switch (args.len) {
             // zig fmt: off

src/codegen/spirv/Assembler.zig

@@ -779,6 +779,40 @@ fn parseValueEnum(self: *Assembler, kind: spec.OperandKind) !void {
 
 fn parseRefId(self: *Assembler) !void {
     const tok = self.currentToken();
+
+    // Handle placeholders that need to be converted to result IDs
+    if (self.eatToken(.placeholder)) {
+        const name = self.tokenText(tok)[1..];
+        const value = self.value_map.get(name) orelse {
+            return self.fail(tok.start, "invalid placeholder '${s}'", .{name});
+        };
+        switch (value) {
+            .string => |str| {
+                // Create a global string constant and use its result ID directly
+                const string_id = try self.spv.constStringGlobal(str);
+                // Create a new entry in the value map with the resolved ID
+                const entry = try self.value_map.getOrPut(self.gpa, name);
+                entry.value_ptr.* = .{ .value = string_id };
+                const index: AsmValue.Ref = @intCast(entry.index);
+                try self.inst.operands.append(self.gpa, .{ .ref_id = index });
+                return;
+            },
+            .constant => {
+                // TODO: Create a constant instruction for the integer
+                return self.fail(tok.start, "integer constants as result IDs not yet supported", .{});
+            },
+            .value => {
+                // This is an argument value - use its result ID directly
+                const entry = try self.value_map.getOrPut(self.gpa, name);
+                // The value should already be resolved, so just use the index
+                const index: AsmValue.Ref = @intCast(entry.index);
+                try self.inst.operands.append(self.gpa, .{ .ref_id = index });
+                return;
+            },
+            else => return self.fail(tok.start, "value '{s}' cannot be used as result-id", .{name}),
+        }
+    }
+
     try self.expectToken(.result_id);
 
     const name = self.tokenText(tok)[1..];