Test compound assignment order of eval (#4606)

Test that the lhs is evaluated before the rhs in a compound assignment
statement.

Author: sudonatalie

src/webgpu/listing_meta.json

@@ -2040,6 +2040,7 @@
   "webgpu:shader,execution,stage:basic_compute:*": { "subcaseMS": 1.000 },
   "webgpu:shader,execution,stage:basic_render:*": { "subcaseMS": 1.000 },
   "webgpu:shader,execution,statement,compound:decl:*": { "subcaseMS": 29.767 },
+  "webgpu:shader,execution,statement,compound:eval_order:*": { "subcaseMS": 54.311 },
   "webgpu:shader,execution,statement,discard:all:*": { "subcaseMS": 36.094 },
   "webgpu:shader,execution,statement,discard:continuing:*": { "subcaseMS": 276.268 },
   "webgpu:shader,execution,statement,discard:derivatives:*": { "subcaseMS": 15.287 },

src/webgpu/shader/execution/statement/compound.spec.ts

@@ -6,6 +6,7 @@ import { makeTestGroup } from '../../../../common/framework/test_group.js';
 import { keysOf } from '../../../../common/util/data_tables.js';
 import { TypedArrayBufferView } from '../../../../common/util/util.js';
 import { AllFeaturesMaxLimitsGPUTest, GPUTest } from '../../../gpu_test.js';
+import { runFlowControlTest } from '../flow_control/harness.js';
 
 export const g = makeTestGroup(AllFeaturesMaxLimitsGPUTest);
 
@@ -135,3 +136,33 @@ g.test('decl')
       kTests[t.params.case].src
     );
   });
+
+g.test('eval_order')
+  .desc('Tests evaluation order of compound assignment, lhs is evaluated before rhs')
+  .fn(t => {
+    runFlowControlTest(t, f => ({
+      entrypoint: `
+arr[0] = 41;
+${f.expect_order(0)}
+arr[idx()] += foo();
+${f.expect_order(3)}
+if (arr[0] == 42) {
+  ${f.expect_order(4)}
+} else {
+  ${f.expect_not_reached()}
+}
+`,
+      extra: `
+var<private> arr : array<u32, 1>;
+fn idx() -> u32 {
+  ${f.expect_order(1)}
+  return 0;
+}
+fn foo() -> u32 {
+  ${f.expect_order(2)}
+  arr[0] = 10;
+  return 1;
+}
+`,
+    }));
+  });