Force index/loop validation on the D3D9 backend

src/libANGLE/renderer/d3d/d3d9/renderer9_utils.cpp

@@ -567,6 +567,11 @@ void GenerateCaps(IDirect3D9 *d3d9,
     // D3D9 has no concept of separate masks and refs for front and back faces in the depth stencil
     // state.
     limitations->noSeparateStencilRefsAndMasks = true;
+
+    // D3D9 shader models have limited support for looping, so the Appendix A
+    // index/loop limitations are necessary. Workarounds that are needed to
+    // support dynamic indexing of vectors on HLSL also don't work on D3D9.
+    limitations->shadersRequireIndexedLoopValidation = true;
 }
 
 }

src/tests/gl_tests/GLSLTest.cpp

@@ -1095,7 +1095,7 @@ TEST_P(GLSLTest, LoopIndexingValidation)
     // If the test is configured to run limited to Feature Level 9_3, then it is
     // assumed that shader compilation will fail with an expected error message containing
     // "Loop index cannot be compared with non-constant expression"
-    if ((GetParam() == ES2_D3D11_FL9_3()))
+    if ((GetParam() == ES2_D3D11_FL9_3() || GetParam() == ES2_D3D9()))
     {
         if (compileResult != 0)
         {