HLSL: allow "sample" as a valid identifier.

HLSL has keywords for various interpolation modifiers such as "linear",
"centroid", "sample", etc.  Of these, "sample" appears to be special,
as it is also accepted as an identifier string, where the others are not.

This PR adds this ability, so the construct "int sample = 42;" no longer
produces a compilation error.

New test = hlsl.identifier.sample.frag

Test/baseResults/hlsl.identifier.sample.frag.out

@@ -0,0 +1,103 @@
+hlsl.identifier.sample.frag
+Shader version: 450
+gl_FragCoord origin is upper left
+0:? Sequence
+0:9  Function Definition: sample(i1; (temp int)
+0:9    Function Parameters: 
+0:9      'x' (in int)
+0:?     Sequence
+0:9      Branch: Return with expression
+0:9        'x' (in int)
+0:12  Function Definition: main( (temp 4-component vector of float)
+0:12    Function Parameters: 
+0:?     Sequence
+0:15      Sequence
+0:15        move second child to first child (temp int)
+0:15          'sample' (temp int)
+0:15          Constant:
+0:15            3 (const int)
+0:17      Sequence
+0:17        move second child to first child (temp 4-component vector of float)
+0:?           '@entryPointOutput' (layout(location=0 ) out 4-component vector of float)
+0:?           Constant:
+0:?             0.000000
+0:?             0.000000
+0:?             0.000000
+0:?             0.000000
+0:17        Branch: Return
+0:?   Linker Objects
+0:?     '@entryPointOutput' (layout(location=0 ) out 4-component vector of float)
+
+
+Linked fragment stage:
+
+
+Shader version: 450
+gl_FragCoord origin is upper left
+0:? Sequence
+0:9  Function Definition: sample(i1; (temp int)
+0:9    Function Parameters: 
+0:9      'x' (in int)
+0:?     Sequence
+0:9      Branch: Return with expression
+0:9        'x' (in int)
+0:12  Function Definition: main( (temp 4-component vector of float)
+0:12    Function Parameters: 
+0:?     Sequence
+0:15      Sequence
+0:15        move second child to first child (temp int)
+0:15          'sample' (temp int)
+0:15          Constant:
+0:15            3 (const int)
+0:17      Sequence
+0:17        move second child to first child (temp 4-component vector of float)
+0:?           '@entryPointOutput' (layout(location=0 ) out 4-component vector of float)
+0:?           Constant:
+0:?             0.000000
+0:?             0.000000
+0:?             0.000000
+0:?             0.000000
+0:17        Branch: Return
+0:?   Linker Objects
+0:?     '@entryPointOutput' (layout(location=0 ) out 4-component vector of float)
+
+// Module Version 10000
+// Generated by (magic number): 80001
+// Id's are bound by 24
+
+                              Capability Shader
+               1:             ExtInstImport  "GLSL.std.450"
+                              MemoryModel Logical GLSL450
+                              EntryPoint Fragment 4  "main" 20
+                              ExecutionMode 4 OriginUpperLeft
+                              Name 4  "main"
+                              Name 10  "sample(i1;"
+                              Name 9  "x"
+                              Name 15  "sample"
+                              Name 20  "@entryPointOutput"
+                              Decorate 20(@entryPointOutput) Location 0
+               2:             TypeVoid
+               3:             TypeFunction 2
+               6:             TypeInt 32 1
+               7:             TypePointer Function 6(int)
+               8:             TypeFunction 6(int) 7(ptr)
+              16:      6(int) Constant 3
+              17:             TypeFloat 32
+              18:             TypeVector 17(float) 4
+              19:             TypePointer Output 18(fvec4)
+20(@entryPointOutput):     19(ptr) Variable Output
+              21:   17(float) Constant 0
+              22:   18(fvec4) ConstantComposite 21 21 21 21
+         4(main):           2 Function None 3
+               5:             Label
+      15(sample):      7(ptr) Variable Function
+                              Store 15(sample) 16
+                              Store 20(@entryPointOutput) 22
+                              Return
+                              FunctionEnd
+  10(sample(i1;):      6(int) Function None 8
+            9(x):      7(ptr) FunctionParameter
+              11:             Label
+              12:      6(int) Load 9(x)
+                              ReturnValue 12
+                              FunctionEnd

Test/hlsl.identifier.sample.frag

@@ -0,0 +1,18 @@
+
+struct MyStruct {
+    sample        float a;
+    noperspective float b;
+    linear        float c;
+    centroid      float d;
+};
+
+int sample(int x) { return x; } // HLSL allows this as an identifier as well.
+
+float4 main() : SV_Target0
+{
+    // HLSL allows this as an identifier as well.
+    // However, this is not true of other qualifier keywords such as "linear".
+    int sample = 3;
+
+    return float4(0,0,0,0);
+}

gtests/Hlsl.FromFile.cpp

@@ -118,6 +118,7 @@ INSTANTIATE_TEST_CASE_P(
         {"hlsl.getdimensions.rw.dx10.frag", "main"},
         {"hlsl.getdimensions.dx10.vert", "main"},
         {"hlsl.getsampleposition.dx10.frag", "main"},
+        {"hlsl.identifier.sample.frag", "main"},
         {"hlsl.if.frag", "PixelShaderFunction"},
         {"hlsl.inoutquals.frag", "main"},
         {"hlsl.init.frag", "ShaderFunction"},

hlsl/hlslGrammar.cpp

@@ -85,6 +85,19 @@ bool HlslGrammar::acceptIdentifier(HlslToken& idToken)
         return true;
     }
 
+    // Even though "sample" is a keyword (for interpolation modifiers), it IS still accepted as
+    // an identifier.  This appears to be a solitary exception: other interp modifier keywords such
+    // as "linear" or "centroid" NOT valid identifiers.  This code special cases "sample",
+    // so e.g, "int sample;" is accepted.
+    if (peekTokenClass(EHTokSample)) {
+        idToken.string     = NewPoolTString("sample");
+        idToken.tokenClass = EHTokIdentifier;
+        idToken.symbol     = nullptr;
+        idToken.loc        = token.loc;
+        advanceToken();
+        return true;
+    }
+
     return false;
 }