Added a workaround for PDBs with empty defines. (#4945)

PDBs compiled with /D "" results in an empty define in the PDB/debug DXIL, which causes IDxcPdbUtils to crash when reading the defines. This change does not fix the empty define, just makes IDxcPdbUtils not crash when reading PDBs like this.

The test consists of a compiled DXIL with embedded debug with an empty define. If we decide to fix the empty define later, this test would continue to test for regression.

(cherry picked from commit ce9b3a2)

Author: adam-yang

tools/clang/tools/dxcompiler/dxcpdbutils.cpp

@@ -716,6 +716,10 @@ struct DxcPdbUtils : public IDxcPdbUtils2, public IDxcPixDxilDebugInfoFactory
   HRESULT AddArgPair(StringRef name, StringRef value) {
     const llvm::opt::OptTable *optTable = hlsl::options::getHlslOptTable();
 
+    // If the value for define is somehow empty, do not add it.
+    if (name == "D" && value.empty())
+      return S_OK;
+
     SmallVector<char, 32> fusedArgStorage;
     if (name.size() && value.size()) {
       // Handling case where old positional arguments used to have

tools/clang/unittests/HLSL/CompilerTest.cpp

@@ -150,6 +150,7 @@ class CompilerTest : public ::testing::Test {
   TEST_METHOD(CompileThenSetRootSignatureThenValidate)
   TEST_METHOD(CompileSetPrivateThenWithStripPrivate)
   TEST_METHOD(CompileWithMultiplePrivateOptionsThenFail)
+  TEST_METHOD(TestPdbUtilsWithEmptyDefine)
 
   void CompileThenTestReflectionThreadSize(const char *source, const WCHAR *target, UINT expectedX, UINT expectedY, UINT expectedZ);
 
@@ -2008,6 +2009,26 @@ TEST_F(CompilerTest, CompileThenTestPdbUtilsEmptyEntry) {
   VERIFY_ARE_EQUAL(pEntryName, L"main");
 }
 
+TEST_F(CompilerTest, TestPdbUtilsWithEmptyDefine) {
+#include "TestHeaders/TestDxilWithEmptyDefine.h"
+  CComPtr<IDxcUtils> pUtils;
+  VERIFY_SUCCEEDED(m_dllSupport.CreateInstance(CLSID_DxcUtils, &pUtils));
+
+  CComPtr<IDxcBlobEncoding> pBlob;
+  VERIFY_SUCCEEDED(pUtils->CreateBlobFromPinned(g_TestDxilWithEmptyDefine, sizeof(g_TestDxilWithEmptyDefine), CP_ACP, &pBlob));
+
+  CComPtr<IDxcPdbUtils> pPdbUtils;
+  VERIFY_SUCCEEDED(m_dllSupport.CreateInstance(CLSID_DxcPdbUtils, &pPdbUtils));
+  VERIFY_SUCCEEDED(pPdbUtils->Load(pBlob));
+
+  UINT32 uCount = 0;
+  VERIFY_SUCCEEDED(pPdbUtils->GetDefineCount(&uCount));
+  for (UINT i = 0; i < uCount; i++) {
+    CComBSTR pDefine;
+    VERIFY_SUCCEEDED(pPdbUtils->GetDefine(i, &pDefine));
+  }
+}
+
 #endif //  _WIN32 - No PDBUtil support
 
 void CompilerTest::TestResourceBindingImpl(