sysgpu: implement select() intrinsic for HLSL, MSL, and SPIR-V

src/sysgpu/shader/codegen/hlsl.zig

@@ -708,6 +708,7 @@ fn emitExpr(hlsl: *Hlsl, inst_idx: InstIndex) error{OutOfMemory}!void {
         .texture_dimension => |inst| try hlsl.emitTextureDimension(inst),
         .texture_load => |inst| try hlsl.emitTextureLoad(inst),
         .texture_store => |inst| try hlsl.emitTextureStore(inst),
+        .select => |inst| try hlsl.emitSelect(inst),
         //else => |inst| std.debug.panic("TODO: implement Air tag {s}", .{@tagName(inst)}),
         else => |inst| std.debug.panic("Expr: {}", .{inst}), // TODO
     }
@@ -1157,6 +1158,17 @@ fn emitTextureStore(hlsl: *Hlsl, inst: Inst.TextureStore) !void {
     try hlsl.emitExpr(inst.value);
 }
 
+fn emitSelect(hlsl: *Hlsl, inst: Inst.BuiltinSelect) !void {
+    // WGSL select(f, t, cond) maps to HLSL (cond ? t : f)
+    try hlsl.writeAll("(");
+    try hlsl.emitExpr(inst.cond);
+    try hlsl.writeAll(" ? ");
+    try hlsl.emitExpr(inst.false);
+    try hlsl.writeAll(" : ");
+    try hlsl.emitExpr(inst.true);
+    try hlsl.writeAll(")");
+}
+
 fn enterScope(hlsl: *Hlsl) void {
     hlsl.indent += 4;
 }

src/sysgpu/shader/codegen/msl.zig

@@ -652,7 +652,7 @@ fn emitDiscard(msl: *Msl) !void {
 fn emitExpr(msl: *Msl, inst_idx: InstIndex) error{ OutOfMemory, ConstExpr }!void {
     switch (msl.air.getInst(inst_idx)) {
         .var_ref => |inst| try msl.emitVarRef(inst),
-        //.bool => |inst| msl.emitBool(inst),
+        .bool => |inst| try msl.emitBool(inst),
         .int => |inst| try msl.emitInt(inst),
         .float => |inst| try msl.emitFloat(inst),
         .vector => |inst| try msl.emitVector(inst),
@@ -675,6 +675,7 @@ fn emitExpr(msl: *Msl, inst_idx: InstIndex) error{ OutOfMemory, ConstExpr }!void
         .texture_dimension => |inst| try msl.emitTextureDimension(inst),
         .texture_load => |inst| try msl.emitTextureLoad(inst),
         .texture_store => |inst| try msl.emitTextureStore(inst),
+        .select => |inst| try msl.emitSelect(inst),
         //else => |inst| std.debug.panic("TODO: implement Air tag {s}", .{@tagName(inst)}),
         else => |inst| try msl.print("Expr: {}", .{inst}), // TODO
     }
@@ -1092,6 +1093,23 @@ fn emitTextureStore(msl: *Msl, inst: Inst.TextureStore) !void {
     try msl.writeAll(")");
 }
 
+fn emitSelect(msl: *Msl, inst: Inst.BuiltinSelect) !void {
+    try msl.writeAll("select(");
+    try msl.emitExpr(inst.true);
+    try msl.writeAll(", ");
+    try msl.emitExpr(inst.false);
+    try msl.writeAll(", ");
+    try msl.emitExpr(inst.cond);
+    try msl.writeAll(")");
+}
+
+fn emitBool(msl: *Msl, inst: Inst.Bool) !void {
+    switch (inst.value.?) {
+        .literal => |lit| try msl.writeAll(if (lit) "true" else "false"),
+        .cast => @panic("TODO: implement bool cast for MSL"),
+    }
+}
+
 fn enterScope(msl: *Msl) void {
     msl.indent += 4;
 }

src/sysgpu/shader/codegen/spirv.zig

@@ -1356,6 +1356,7 @@ fn emitExpr(spv: *SpirV, section: *Section, inst: InstIndex) error{OutOfMemory}!
         .texture_sample => |ts| spv.emitTextureSample(section, ts),
         .texture_dimension => |td| spv.emitTextureDimension(section, td),
         .texture_load => |tl| spv.emitTextureLoad(section, tl),
+        .select => |sel| spv.emitSelect(section, sel),
         else => std.debug.panic("TODO: implement Air tag {s}", .{@tagName(spv.air.getInst(inst))}),
     };
 }
@@ -2460,6 +2461,25 @@ fn emitArray(spv: *SpirV, section: *Section, inst: Inst.Array) !IdRef {
     return id;
 }
 
+fn emitSelect(spv: *SpirV, section: *Section, inst: Inst.BuiltinSelect) !IdRef {
+    const cond_id = try spv.emitExpr(section, inst.cond);
+    const true_id = try spv.emitExpr(section, inst.true);
+    const false_id = try spv.emitExpr(section, inst.false);
+
+    const result_type_id = try spv.emitType(inst.type);
+
+    const id = spv.allocId();
+    try section.emit(.OpSelect, .{
+        .id_result_type = result_type_id,
+        .id_result = id,
+        .condition = cond_id,
+        .object_1 = false_id,
+        .object_2 = true_id,
+    });
+
+    return id;
+}
+
 const Key = union(enum) {
     void_type,
     bool_type,

src/sysgpu/shader/test.zig

@@ -261,6 +261,15 @@ test "vertexWriteGBuffers" {
     // try expectCodegen(vertexWriteGBuffers, "triangle.glsl", .glsl, false);
 }
 
+test "select" {
+    const src = @embedFile("test/select.wgsl");
+
+    try expectCodegen(src, "select.spv", .spirv, false);
+    try expectCodegen(src, "select.hlsl", .hlsl, false);
+    try expectCodegen(src, "select.msl", .msl, false);
+    //try expectCodegen(src, "select.glsl", .glsl, false); // I guess no glsl based on the other tests
+}
+
 fn expectCodegen(
     source: [:0]const u8,
     comptime file_name: []const u8,

src/sysgpu/shader/test/select.wgsl

@@ -0,0 +1,8 @@
+@fragment
+fn main() -> @location(0) vec4<f32> {
+    var cond = true;
+    var t = vec4<f32>(1.0, 1.0, 1.0, 1.0);
+    var f = vec4<f32>(0.0, 0.0, 0.0, 0.0);
+
+    return select(f, t, cond);
+}