Change default validation behavior (#7392)

This PR changes the default validation behavior to use the internal
validator by default.
If no options are specified, the internal validator will be used, and if
it fails, then compilation fails.
The external validator can still be run but must be explicitly chosen.
Specifying internal works just as before.

There is plenty of testing and infrastructure that needs to be added to
verify this change, but that needs to be added in a separate change.
This change is step 1.

Addresses #7389

Author: bob80905

include/dxc/Support/HLSLOptions.h

@@ -115,7 +115,7 @@ struct RewriterOpts {
 };
 
 enum class ValidatorSelection : int {
-  Auto,        // Try DXIL.dll; fallback to internal validator
+  Auto,        // Force internal validator (even if DXIL.dll is present)
   Internal,    // Force internal validator (even if DXIL.dll is present)
   External,    // Use DXIL.dll, failing compilation if not available
   Invalid = -1 // Invalid

tools/clang/tools/dxcompiler/dxcutil.cpp

@@ -49,23 +49,33 @@ HRESULT RunInternalValidator(IDxcValidator *pValidator,
 namespace {
 // AssembleToContainer helper functions.
 
+// return true if the internal validator was used, false otherwise
 bool CreateValidator(CComPtr<IDxcValidator> &pValidator,
                      hlsl::options::ValidatorSelection SelectValidator =
                          hlsl::options::ValidatorSelection::Auto) {
   bool bInternal =
       SelectValidator == hlsl::options::ValidatorSelection::Internal;
   bool bExternal =
       SelectValidator == hlsl::options::ValidatorSelection::External;
-  if (!bInternal && DxilLibIsEnabled())
-    DxilLibCreateInstance(CLSID_DxcValidator, &pValidator);
+  bool bAuto = SelectValidator == hlsl::options::ValidatorSelection::Auto;
 
-  bool bInternalValidator = false;
-  if (pValidator == nullptr) {
-    IFTBOOL(!bExternal, DXC_E_VALIDATOR_MISSING);
+  // default behavior uses internal validator, as well as
+  // explicitly specifying internal
+  if (bInternal || bAuto) {
     IFT(CreateDxcValidator(IID_PPV_ARGS(&pValidator)));
-    bInternalValidator = true;
+    return true;
+  }
+
+  if (bExternal) {
+    // if external was explicitly specified, but no
+    // external validator could be found (no DXIL.dll), then error
+    IFTBOOL(DxilLibIsEnabled(), DXC_E_VALIDATOR_MISSING);
+    IFT(DxilLibCreateInstance(CLSID_DxcValidator, &pValidator));
+
+    return false;
   }
-  return bInternalValidator;
+
+  return false;
 }
 
 } // namespace