[WGSL] Variables initializer shouldn't be a reference

https://bugs.webkit.org/show_bug.cgi?id=257601
rdar://110105334

Reviewed by Mike Wyrzykowski.

When initializing a variable, the value used to initialize it should be unpacked
if it's a reference. E.g.:

var a = 0;
var b = a;
b = 1;

The above program should not change the value of `a`, and references to `b` should
have type `ref<i32>`, not `ref<ref<i32>>`. In order to fix that, when we infer the
type of a variable initializer (which doesn't have an explicit type annotation), if
the is a reference (as it would be for `a` in the example above, which would have type
`ref<i32>`), we should use the referenced type instead (i.e. `i32` in this example)

* Source/WebGPU/WGSL/TypeCheck.cpp:
(WGSL::TypeChecker::visitVariable):

Canonical link: https://commits.webkit.org/264860@main

Source/WebGPU/WGSL/TypeCheck.cpp

@@ -226,6 +226,11 @@ void TypeChecker::visitVariable(AST::Variable& variable, VariableKind variableKi
         result = resolve(*variable.maybeTypeName());
     if (variable.maybeInitializer()) {
         auto* initializerType = infer(*variable.maybeInitializer());
+        if (auto* reference = std::get_if<Types::Reference>(initializerType)) {
+            initializerType = reference->element;
+            variable.maybeInitializer()->m_inferredType = initializerType;
+        }
+
         if (!result)
             result = initializerType;
         else if (unify(result, initializerType))

Source/WebGPU/WGSL/tests/valid/var-initialization-with-var.wgsl

@@ -0,0 +1,15 @@
+// RUN: %metal main 2>&1 | %check
+
+fn f(x: f32) { }
+
+@compute @workgroup_size(1)
+fn main() {
+  // CHECK: float local\d+ = 1
+  var a = 1.0;
+  // CHECK: float local\d+ = local\d
+  var b = a;
+  // CHECK: local\d+ = 0
+  b = 0.0;
+  // CHECK: f\(local\d+\)
+  _ = f(b);
+}