Add != operator for enum types (shader-slang#1394)

This was an oversight in the stdlib, and the `!=` definition follows the `==` in a straightforward fashion.

Author: Tim Foley

source/slang/core.meta.slang

@@ -1808,6 +1808,10 @@ __generic<E : __EnumType>
 __intrinsic_op($(kIROp_Eql))
 bool operator==(E left, E right);
 
+__generic<E : __EnumType>
+__intrinsic_op($(kIROp_Neq))
+bool operator!=(E left, E right);
+
 // Binding Attributes
 
 __attributeTarget(DeclBase)

tests/language-feature/enums/enum-equality.slang

@@ -0,0 +1,40 @@
+// enum-equality.slang
+
+// Test that equality (and inequality) of `enum`
+// types works as expected.
+
+//TEST(compute):COMPARE_COMPUTE:
+
+enum Channel
+{
+    Red,
+    Green,
+    Blue,
+    Alpha,
+}
+
+int test(int val)
+{
+    Channel channel= Channel(val);
+
+    int result = 0;
+    if(channel == Channel.Red)      result += 1;
+    if(channel != Channel.Green)    result += 16;
+    if(channel == Channel.Blue)     result += 16*16;
+    if(channel != Channel.Alpha)    result += 16*16*16;
+
+    return result;
+}
+
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    uint tid = dispatchThreadID.x;
+    int inVal = tid;
+    int outVal = test(inVal);
+    outputBuffer[tid] = outVal;
+}

tests/language-feature/enums/enum-equality.slang.expected.txt

@@ -0,0 +1,4 @@
+1011
+1000
+1110
+10