test fixture: print optimized assembly that fails to validate (KhronosGroup#6043)

In a spirv-opt pass test that does validation, disassemble the
text first. So if validation fails, print the spir-v assembly
that fails to validate.

Author: dneto0

test/opt/pass_fixture.h

@@ -122,23 +122,24 @@ class PassTest : public TestT {
     auto status = Pass::Status::SuccessWithoutChange;
     std::tie(optimized_bin, status) = SinglePassRunToBinary<PassT>(
         assembly, skip_nop, std::forward<Args>(args)...);
+    std::string optimized_asm;
+    SpirvTools tools(env_);
+    EXPECT_TRUE(
+        tools.Disassemble(optimized_bin, &optimized_asm, disassemble_options_))
+        << "Disassembling failed for shader:\n"
+        << assembly << std::endl;
     if (do_validation) {
       spv_context spvContext = spvContextCreate(env_);
       spv_diagnostic diagnostic = nullptr;
       spv_const_binary_t binary = {optimized_bin.data(), optimized_bin.size()};
       spv_result_t error = spvValidateWithOptions(
           spvContext, ValidatorOptions(), &binary, &diagnostic);
-      EXPECT_EQ(error, 0);
+      EXPECT_EQ(error, 0) << "validation failed for optimized asm:\n"
+                          << optimized_asm;
       if (error != 0) spvDiagnosticPrint(diagnostic);
       spvDiagnosticDestroy(diagnostic);
       spvContextDestroy(spvContext);
     }
-    std::string optimized_asm;
-    SpirvTools tools(env_);
-    EXPECT_TRUE(
-        tools.Disassemble(optimized_bin, &optimized_asm, disassemble_options_))
-        << "Disassembling failed for shader:\n"
-        << assembly << std::endl;
     return std::make_tuple(optimized_asm, status);
   }