[ir] Validate switch results

Fixes a fuzzer issue where the result was invalid.

Fixed: 441682088
Change-Id: I06198550269396c98f6c9d551162e76ecd4f7a1d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/259856
Auto-Submit: James Price <jrprice@google.com>
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

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

diff --git a/src/tint/lang/core/ir/validator.cc b/src/tint/lang/core/ir/validator.cc
index 9cc9d0c..d2f25e5f 100644
--- a/src/tint/lang/core/ir/validator.cc
+++ b/src/tint/lang/core/ir/validator.cc
@@ -3558,6 +3558,7 @@
 }
 
 void Validator::CheckSwitch(const Switch* s) {
+    CheckResults(s);
     CheckOperand(s, Switch::kConditionOperandOffset);
 
     if (s->Condition() && !s->Condition()->Type()->IsIntegerScalar()) {

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

diff --git a/src/tint/lang/core/ir/validator_flow_control_test.cc b/src/tint/lang/core/ir/validator_flow_control_test.cc
index b49da34..a098bc3 100644
--- a/src/tint/lang/core/ir/validator_flow_control_test.cc
+++ b/src/tint/lang/core/ir/validator_flow_control_test.cc
@@ -2134,4 +2134,23 @@
 )")) << res.Failure();
 }
 
+TEST_F(IR_ValidatorTest, Switch_NullResult) {
+    auto* f = b.Function("my_func", ty.void_());
+
+    b.Append(f->Block(), [&] {
+        auto* s = b.Switch(1_u);
+        s->SetResults(Vector<InstructionResult*, 1>{nullptr});
+
+        b.Append(b.DefaultCase(s), [&] { b.Return(f); });
+        b.Return(f);
+    });
+
+    auto res = ir::Validate(mod);
+    ASSERT_NE(res, Success);
+    EXPECT_THAT(res.Failure().reason, testing::HasSubstr(R"(error: switch: result is undefined
+    undef = switch 1u [c: (default, $B2)] {  # switch_1
+    ^^^^^
+)")) << res.Failure();
+}
+
 }  // namespace tint::core::ir