[clang] [llvm] [HLSL] Implement the `faceforward` intrinsic (PR #135878)

[Finn Plummer via llvm-commits]

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@@ -137,6 +137,42 @@ bool SemaSPIRV::CheckSPIRVBuiltinFunctionCall(unsigned BuiltinID,
     TheCall->setType(RetTy);
     break;
   }
+  case SPIRV::BI__builtin_spirv_faceforward: {
+    if (SemaRef.checkArgCount(TheCall, 3))
+      return true;
+
+    // check if all arguments have floating representation
+    for (unsigned i = 0; i < TheCall->getNumArgs(); ++i) {
+      ExprResult Arg = TheCall->getArg(i);
+      QualType ArgTy = Arg.get()->getType();
+      if (!ArgTy->hasFloatingRepresentation()) {
+        SemaRef.Diag(Arg.get()->getBeginLoc(),
+                     diag::err_builtin_invalid_arg_type)
+            << i + 1 << /* scalar or vector */ 5 << /* no int */ 0 << /* fp */ 1
+            << ArgTy;
+        return true;
+      }
+    }
+
+    // check if all arguments are of the same type
+    ExprResult A = TheCall->getArg(0);
+    ExprResult B = TheCall->getArg(1);
+    ExprResult C = TheCall->getArg(2);
+    if (!(SemaRef.getASTContext().hasSameUnqualifiedType(A.get()->getType(),
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inbelic wrote:

Same here, could be common function. See the `CheckAllArgsHaveTheSameType` in `SemaHLSL`. You could probably just copy paste that into this file. I think we previously decided to NOT move them to a common place so I wouldn't worry about doing that.

https://github.com/llvm/llvm-project/pull/135878