[tint][ir][val] Check access type exists before dereferencing

Fixes: 376084082
Change-Id: Ic264d30585789ac5ecf097f233f7568a61bf1dcc
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/212935
Reviewed-by: dan sinclair <[email protected]>
Commit-Queue: Ryan Harrison <[email protected]>
Auto-Submit: Ryan Harrison <[email protected]>

src/tint/lang/core/ir/validator.cc

@@ -2383,8 +2383,9 @@ void Validator::CheckAccess(const Access* a) {
         };
 
         auto* index = a->Indices()[i];
-        if (DAWN_UNLIKELY(!index->Type()->IsIntegerScalar())) {
-            err() << "index must be integer, got " << index->Type()->FriendlyName();
+        if (DAWN_UNLIKELY(!index->Type() || !index->Type()->IsIntegerScalar())) {
+            err() << "index must be integer, got "
+                  << (index->Type() ? index->Type()->FriendlyName() : "undefined");
             return;
         }
 
@@ -2397,7 +2398,7 @@ void Validator::CheckAccess(const Access* a) {
 
         if (auto* const_index = index->As<ir::Constant>()) {
             auto* value = const_index->Value();
-            if (value->Type()->IsSignedIntegerScalar()) {
+            if (!value->Type() || value->Type()->IsSignedIntegerScalar()) {
                 // index is a signed integer scalar. Check that the index isn't negative.
                 // If the index is unsigned, we can skip this.
                 auto idx = value->ValueAs<AInt>();