[HLSL] Implementation of the frac intrinsic

clang/include/clang/Basic/Builtins.td

@@ -4536,6 +4536,12 @@ def HLSLDotProduct : LangBuiltin<"HLSL_LANG"> {
   let Prototype = "void(...)";
 }
 
+def HLSLFrac : LangBuiltin<"HLSL_LANG"> {
+  let Spellings = ["__builtin_hlsl_elementwise_frac"];
+  let Attributes = [NoThrow, Const];
+  let Prototype = "void(...)";
+}
+
 def HLSLLerp : LangBuiltin<"HLSL_LANG"> {
   let Spellings = ["__builtin_hlsl_lerp"];
   let Attributes = [NoThrow, Const];

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10270,7 +10270,7 @@ def err_vec_builtin_non_vector_all : Error<
  "all arguments to %0 must be vectors">;
 def err_vec_builtin_incompatible_vector_all : Error<
   "all arguments to %0 must have vectors of the same type">;
-  
+
 def err_vec_builtin_non_vector : Error<
  "first two arguments to %0 must be vectors">;
 def err_vec_builtin_incompatible_vector : Error<

clang/lib/CodeGen/CGBuiltin.cpp

@@ -18020,14 +18020,7 @@ Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID,
         V = Builder.CreateFMul(S, V);
         return Builder.CreateFAdd(X, V, "dx.lerp");
       }
-      // DXC does this via casting to float should we do the same thing?
-      if (Xty->isIntegerTy()) {
-        auto V = Builder.CreateSub(Y, X);
-        V = Builder.CreateMul(S, V);
-        return Builder.CreateAdd(X, V, "dx.lerp");
-      }
-      // Bools should have been promoted
-      llvm_unreachable("Scalar Lerp is only supported on ints and floats.");
+      llvm_unreachable("Scalar Lerp is only supported on floats.");
     }
     // A VectorSplat should have happened
     assert(Xty->isVectorTy() && Yty->isVectorTy() && Sty->isVectorTy() &&
@@ -18041,12 +18034,24 @@ Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID,
         E->getArg(2)->getType()->getAs<VectorType>();
     // A HLSLVectorTruncation should have happend
     assert(XVecTy->getNumElements() == YVecTy->getNumElements() &&
-           SVecTy->getNumElements() &&
+           XVecTy->getNumElements() == SVecTy->getNumElements() &&
            "Lerp requires vectors to be of the same size.");
+    assert(XVecTy->getElementType()->isRealFloatingType() &&
+           XVecTy->getElementType() == YVecTy->getElementType() &&
+           XVecTy->getElementType() == SVecTy->getElementType() &&
+           "Lerp requires float vectors to be of the same type.");
     return Builder.CreateIntrinsic(
         /*ReturnType*/ Xty, Intrinsic::dx_lerp, ArrayRef<Value *>{X, Y, S},
         nullptr, "dx.lerp");
   }
+  case Builtin::BI__builtin_hlsl_elementwise_frac: {
+    Value *Op0 = EmitScalarExpr(E->getArg(0));
+    if (!E->getArg(0)->getType()->hasFloatingRepresentation())
+      llvm_unreachable("frac operand must have a float representation");
+    return Builder.CreateIntrinsic(
+        /*ReturnType*/ Op0->getType(), Intrinsic::dx_frac,
+        ArrayRef<Value *>{Op0}, nullptr, "dx.frac");
+  }
   }
   return nullptr;
 }

clang/lib/Headers/hlsl/hlsl_intrinsics.h

@@ -317,6 +317,38 @@ double3 floor(double3);
 _HLSL_BUILTIN_ALIAS(__builtin_elementwise_floor)
 double4 floor(double4);
 
+//===----------------------------------------------------------------------===//
+// frac builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn T frac(T x)
+/// \brief Returns the fractional (or decimal) part of x. \a x parameter.
+/// \param x The specified input value.
+///
+/// If \a the return value is greater than or equal to 0 and less than 1.
+
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_frac)
+half frac(half);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_frac)
+half2 frac(half2);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_frac)
+half3 frac(half3);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_frac)
+half4 frac(half4);
+
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_frac)
+float frac(float);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_frac)
+float2 frac(float2);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_frac)
+float3 frac(float3);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_frac)
+float4 frac(float4);
+
 //===----------------------------------------------------------------------===//
 // lerp builtins
 //===----------------------------------------------------------------------===//

clang/lib/Sema/SemaChecking.cpp

@@ -5246,6 +5246,23 @@ bool CheckVectorElementCallArgs(Sema *S, CallExpr *TheCall) {
   return true;
 }
 
+bool CheckAllArgsHaveFloatRepresentation(Sema *S, CallExpr *TheCall) {
+  QualType ExpectedType = S->Context.FloatTy;
+  for (unsigned i = 0; i < TheCall->getNumArgs(); ++i) {
+    QualType PassedType = TheCall->getArg(i)->getType();
+    if (!PassedType->hasFloatingRepresentation()) {
+      if (auto *VecTyA = PassedType->getAs<VectorType>())
+        ExpectedType = S->Context.getVectorType(
+            ExpectedType, VecTyA->getNumElements(), VecTyA->getVectorKind());
+      S->Diag(TheCall->getArg(0)->getBeginLoc(),
+              diag::err_typecheck_convert_incompatible)
+          << PassedType << ExpectedType << 1 << 0 << 0;
+      return true;
+    }
+  }
+  return false;
+}
+
 // Note: returning true in this case results in CheckBuiltinFunctionCall
 // returning an ExprError
 bool Sema::CheckHLSLBuiltinFunctionCall(unsigned BuiltinID, CallExpr *TheCall) {
@@ -5259,13 +5276,22 @@ bool Sema::CheckHLSLBuiltinFunctionCall(unsigned BuiltinID, CallExpr *TheCall) {
       return true;
     break;
   }
+  case Builtin::BI__builtin_hlsl_elementwise_frac: {
+    if (PrepareBuiltinElementwiseMathOneArgCall(TheCall))
+      return true;
+    if (CheckAllArgsHaveFloatRepresentation(this, TheCall))
+      return true;
+    break;
+  }
   case Builtin::BI__builtin_hlsl_lerp: {
     if (checkArgCount(*this, TheCall, 3))
       return true;
     if (CheckVectorElementCallArgs(this, TheCall))
       return true;
     if (SemaBuiltinElementwiseTernaryMath(TheCall))
       return true;
+    if (CheckAllArgsHaveFloatRepresentation(this, TheCall))
+      return true;
     break;
   }
   }