[Bug] Add COMPARISON_NONE; fix the error message related to it (microsoft#8245)

### Bug Description

Regarding the sampler descriptions, I found two issues:
1. D3D12_COMPARISON_FUNC_NONE should be added; it is a valid value for
the non-comparison samplers.
2. The error message should be revised; the original one shows
"**Unexpected texture address mode value**", which is confusing.

### Comments

1. D3D12_COMPARISON_FUNC_NONE is a valid enumerator. It's listed in
d3d12.h.
2. I verified this value by PIX; the result shown below confirmed my
expectation.

<img width="491" height="335" alt="image"
src="https://github.com/user-attachments/assets/ebaf3b97-b62e-4892-b9d9-80e4241998c3"
/>

Author: ModulePillow

include/dxc/DxilRootSignature/DxilRootSignature.h

@@ -55,6 +55,7 @@ static const uint32_t DxilMapAnisotropy = 16;
 
 // Enumerations and flags.
 enum class DxilComparisonFunc : unsigned {
+  None = 0,
   Never = 1,
   Less = 2,
   Equal = 3,

tools/clang/lib/Parse/HLSLRootSignature.cpp

@@ -232,8 +232,8 @@ void RootSignatureTokenizer::ReadNextToken(uint32_t BufferIdx) {
     break;
 
   case 'C':
-    bKW = KW(CBV) || KW(comparisonFunc) || KW(COMPARISON_NEVER) ||
-          KW(COMPARISON_LESS) || KW(COMPARISON_EQUAL) ||
+    bKW = KW(CBV) || KW(comparisonFunc) || KW(COMPARISON_NONE) ||
+          KW(COMPARISON_NEVER) || KW(COMPARISON_LESS) || KW(COMPARISON_EQUAL) ||
           KW(COMPARISON_LESS_EQUAL) || KW(COMPARISON_GREATER) ||
           KW(COMPARISON_NOT_EQUAL) || KW(COMPARISON_GREATER_EQUAL) ||
           KW(COMPARISON_ALWAYS) || KW(CBV_SRV_UAV_HEAP_DIRECTLY_INDEXED);
@@ -1613,6 +1613,9 @@ HRESULT RootSignatureParser::ParseComparisonFunction(
   Token = m_pTokenizer->GetToken();
 
   switch (Token.GetType()) {
+  case TokenType::COMPARISON_NONE:
+    ComparisonFunc = DxilComparisonFunc::None;
+    break;
   case TokenType::COMPARISON_NEVER:
     ComparisonFunc = DxilComparisonFunc::Never;
     break;
@@ -1639,7 +1642,7 @@ HRESULT RootSignatureParser::ParseComparisonFunction(
     break;
   default:
     IFC(Error(ERR_RS_UNEXPECTED_TOKEN,
-              "Unexpected texture address mode value: '%s'.", Token.GetStr()));
+              "Unexpected comparison function value: '%s'.", Token.GetStr()));
   }
 
 Cleanup:
@@ -1672,8 +1675,8 @@ RootSignatureParser::ParseBorderColor(DxilStaticBorderColor &BorderColor) {
     BorderColor = DxilStaticBorderColor::OpaqueWhiteUint;
     break;
   default:
-    IFC(Error(ERR_RS_UNEXPECTED_TOKEN,
-              "Unexpected texture address mode value: '%s'.", Token.GetStr()));
+    IFC(Error(ERR_RS_UNEXPECTED_TOKEN, "Unexpected border color value: '%s'.",
+              Token.GetStr()));
   }
 
 Cleanup:

tools/clang/lib/Parse/HLSLRootSignature.h

@@ -139,6 +139,7 @@ class RootSignatureTokenizer {
 
       // Comparison function
       comparisonFunc,
+      COMPARISON_NONE,
       COMPARISON_NEVER,
       COMPARISON_LESS,
       COMPARISON_EQUAL,

tools/clang/unittests/HLSL/FunctionTest.cpp

@@ -681,6 +681,8 @@ TEST_F(FunctionTest, ParseRootSignature) {
   // MaxAnisotropy
   TestHLSLRootSignatureCase("StaticSampler(s2, maxAnisotropy=2)", S_OK);
   // Comparison function
+  TestHLSLRootSignatureCase(
+      "StaticSampler(ComparisonFunc = COMPARISON_NONE, s2)", S_OK);
   TestHLSLRootSignatureCase(
       "StaticSampler(ComparisonFunc = COMPARISON_NEVER, s2)", S_OK);
   TestHLSLRootSignatureCase(

tools/clang/unittests/HLSLExec/ShaderOpTest.cpp

@@ -1704,6 +1704,7 @@ static const ParserEnumValue TEXTURE_ADDRESS_MODE_TABLE[] = {
 };
 
 static const ParserEnumValue COMPARISON_FUNC_TABLE[] = {
+    {L"NONE", D3D12_COMPARISON_FUNC_NONE},
     {L"NEVER", D3D12_COMPARISON_FUNC_NEVER},
     {L"LESS", D3D12_COMPARISON_FUNC_LESS},
     {L"EQUAL", D3D12_COMPARISON_FUNC_EQUAL},