[ir][fuzz] Handle invalid workgroup sizes in fuzzer.

Then wokgroup size is checked by Dawn and Tint exe outside of the tint
backend. Add a similar check into the WGSL fuzzer so we don't fail with
a validation error.

This is not checked in the const-eval code for SubstituteOverrides
because Dawn needs the result of the const-eval to do it's own checks,
and shouldn't fail before it does so.

Bug: 408370947
Change-Id: I7ae3011c314e0d1abac068e2b34bdd95031271d5
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/235334
Auto-Submit: dan sinclair <dsinclair@chromium.org>
Reviewed-by: James Price <jrprice@google.com>
Commit-Queue: James Price <jrprice@google.com>

src/tint/cmd/fuzz/ir/fuzz.cc

diff --git a/src/tint/cmd/fuzz/ir/fuzz.cc b/src/tint/cmd/fuzz/ir/fuzz.cc
index 7925cc8..f01c25c 100644
--- a/src/tint/cmd/fuzz/ir/fuzz.cc
+++ b/src/tint/cmd/fuzz/ir/fuzz.cc
@@ -88,6 +88,25 @@
                 return;
             }
 
+            // Workgroup sizes < 1 are checked by Dawn and the Tint binary,
+            // should be skipped by the fuzzer.
+            for (auto func : ir->functions) {
+                if (func->Stage() != tint::core::ir::Function::PipelineStage::kCompute) {
+                    continue;
+                }
+
+                auto wg = func->WorkgroupSize().value();
+                for (auto value : wg) {
+                    auto* cnst = value->As<core::ir::Constant>();
+                    TINT_ASSERT(cnst);
+
+                    auto val = cnst->Value()->ValueAs<int32_t>();
+                    if (val < 1) {
+                        return;
+                    }
+                }
+            }
+
             if (auto val = core::ir::Validate(ir.Get()); val != Success) {
                 TINT_ICE() << val.Failure();
             }