[HLSL] Implementation lerp intrinsic

This is the start of implementing the lerp intrinsic
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-lerp
Builtins.td - defines the builtin
hlsl_intrinsics.h - defines the lerp api
DiagnosticSemaKinds.td - needed a new error to be inclusive for more
than two operands.
CGBuiltin.cpp - add the lerp intrinsic lowering
SemaChecking.cpp - type checks for lerp builtin
IntrinsicsDirectX.td - define the lerp intrinsic

this change implements the first half of #70102

Author: farzonl

clang/include/clang/Basic/Builtins.td

@@ -4530,6 +4530,12 @@ def HLSLDotProduct : LangBuiltin<"HLSL_LANG"> {
   let Prototype = "void(...)";
 }
 
+def HLSLLerp : LangBuiltin<"HLSL_LANG"> {
+  let Spellings = ["__builtin_hlsl_lerp"];
+  let Attributes = [NoThrow, Const];
+  let Prototype = "void(...)";
+}
+
 // Builtins for XRay.
 def XRayCustomEvent : Builtin {
   let Spellings = ["__xray_customevent"];

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10266,6 +10266,11 @@ def err_block_on_vm : Error<
 def err_sizeless_nonlocal : Error<
   "non-local variable with sizeless type %0">;
 
+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

@@ -18006,6 +18006,43 @@ Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID,
         /*ReturnType*/ T0->getScalarType(), Intrinsic::dx_dot,
         ArrayRef<Value *>{Op0, Op1}, nullptr, "dx.dot");
   } break;
+  case Builtin::BI__builtin_hlsl_lerp: {
+    Value *X = EmitScalarExpr(E->getArg(0));
+    Value *Y = EmitScalarExpr(E->getArg(1));
+    Value *S = EmitScalarExpr(E->getArg(2));
+    llvm::Type *Xty = X->getType();
+    llvm::Type *Yty = Y->getType();
+    llvm::Type *Sty = S->getType();
+    if (!Xty->isVectorTy() && !Yty->isVectorTy() && !Sty->isVectorTy()) {
+      if (Xty->isFloatingPointTy()) {
+        auto V = Builder.CreateFSub(Y, X);
+        V = Builder.CreateFMul(S, V);
+        return Builder.CreateFAdd(X, V, "dx.lerp");
+      }
+      llvm_unreachable("Scalar Lerp is only supported on floats.");
+    }
+    // A VectorSplat should have happened
+    assert(Xty->isVectorTy() && Yty->isVectorTy() && Sty->isVectorTy() &&
+           "Lerp of vector and scalar is not supported.");
+
+    [[maybe_unused]] auto *XVecTy =
+        E->getArg(0)->getType()->getAs<VectorType>();
+    [[maybe_unused]] auto *YVecTy =
+        E->getArg(1)->getType()->getAs<VectorType>();
+    [[maybe_unused]] auto *SVecTy =
+        E->getArg(2)->getType()->getAs<VectorType>();
+    // A HLSLVectorTruncation should have happend
+    assert(XVecTy->getNumElements() == YVecTy->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");
+  }
   }
   return nullptr;
 }

clang/lib/Headers/hlsl/hlsl_intrinsics.h

@@ -317,6 +317,42 @@ double3 floor(double3);
 _HLSL_BUILTIN_ALIAS(__builtin_elementwise_floor)
 double4 floor(double4);
 
+//===----------------------------------------------------------------------===//
+// lerp builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn T lerp(T x, T y, T s)
+/// \brief Returns the linear interpolation of x to y by s.
+/// \param x [in] The first-floating point value.
+/// \param y [in] The second-floating point value.
+/// \param s [in] A value that linearly interpolates between the x parameter and
+/// the y parameter.
+///
+/// Linear interpolation is based on the following formula: x*(1-s) + y*s which
+/// can equivalently be written as x + s(y-x).
+
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_lerp)
+half lerp(half, half, half);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_lerp)
+half2 lerp(half2, half2, half2);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_lerp)
+half3 lerp(half3, half3, half3);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_lerp)
+half4 lerp(half4, half4, half4);
+
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_lerp)
+float lerp(float, float, float);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_lerp)
+float2 lerp(float2, float2, float2);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_lerp)
+float3 lerp(float3, float3, float3);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_lerp)
+float4 lerp(float4, float4, float4);
+
 //===----------------------------------------------------------------------===//
 // log builtins
 //===----------------------------------------------------------------------===//

clang/lib/Sema/SemaChecking.cpp

@@ -5169,49 +5169,63 @@ bool Sema::CheckPPCMMAType(QualType Type, SourceLocation TypeLoc) {
 bool CheckVectorElementCallArgs(Sema *S, CallExpr *TheCall) {
   assert(TheCall->getNumArgs() > 1);
   ExprResult A = TheCall->getArg(0);
-  ExprResult B = TheCall->getArg(1);
+
   QualType ArgTyA = A.get()->getType();
-  QualType ArgTyB = B.get()->getType();
+
   auto *VecTyA = ArgTyA->getAs<VectorType>();
-  auto *VecTyB = ArgTyB->getAs<VectorType>();
   SourceLocation BuiltinLoc = TheCall->getBeginLoc();
-  if (VecTyA == nullptr && VecTyB == nullptr)
-    return false;
 
-  if (VecTyA && VecTyB) {
-    bool retValue = false;
-    if (VecTyA->getElementType() != VecTyB->getElementType()) {
-      // Note: type promotion is intended to be handeled via the intrinsics
-      //  and not the builtin itself.
-      S->Diag(TheCall->getBeginLoc(), diag::err_vec_builtin_incompatible_vector)
-          << TheCall->getDirectCallee()
-          << SourceRange(A.get()->getBeginLoc(), B.get()->getEndLoc());
-      retValue = true;
-    }
-    if (VecTyA->getNumElements() != VecTyB->getNumElements()) {
-      // if we get here a HLSLVectorTruncation is needed.
-      S->Diag(BuiltinLoc, diag::err_vec_builtin_incompatible_vector)
-          << TheCall->getDirectCallee()
-          << SourceRange(TheCall->getArg(0)->getBeginLoc(),
-                         TheCall->getArg(1)->getEndLoc());
-      retValue = true;
-    }
+  for (unsigned i = 1; i < TheCall->getNumArgs(); ++i) {
+    ExprResult B = TheCall->getArg(i);
+    QualType ArgTyB = B.get()->getType();
+    auto *VecTyB = ArgTyB->getAs<VectorType>();
+    if (VecTyA == nullptr && VecTyB == nullptr)
+      return false;
 
-    if (retValue)
-      TheCall->setType(VecTyA->getElementType());
+    if (VecTyA && VecTyB) {
+      bool retValue = false;
+      if (VecTyA->getElementType() != VecTyB->getElementType()) {
+        // Note: type promotion is intended to be handeled via the intrinsics
+        //  and not the builtin itself.
+        S->Diag(TheCall->getBeginLoc(),
+                diag::err_vec_builtin_incompatible_vector_all)
+            << TheCall->getDirectCallee()
+            << SourceRange(A.get()->getBeginLoc(), B.get()->getEndLoc());
+        retValue = true;
+      }
+      if (VecTyA->getNumElements() != VecTyB->getNumElements()) {
+        // if we get here a HLSLVectorTruncation is needed.
+        S->Diag(BuiltinLoc, diag::err_vec_builtin_incompatible_vector_all)
+            << TheCall->getDirectCallee()
+            << SourceRange(TheCall->getArg(0)->getBeginLoc(),
+                           TheCall->getArg(1)->getEndLoc());
+        retValue = true;
+      }
+
+      if (!retValue)
+        TheCall->setType(VecTyA->getElementType());
 
-    return retValue;
+      return retValue;
+    }
   }
 
   // Note: if we get here one of the args is a scalar which
   // requires a VectorSplat on Arg0 or Arg1
-  S->Diag(BuiltinLoc, diag::err_vec_builtin_non_vector)
+  S->Diag(BuiltinLoc, diag::err_vec_builtin_non_vector_all)
       << TheCall->getDirectCallee()
       << SourceRange(TheCall->getArg(0)->getBeginLoc(),
                      TheCall->getArg(1)->getEndLoc());
   return true;
 }
 
+bool checkAllArgsAreFloatRepresnations(CallExpr *TheCall) {
+  for (unsigned i = 0; i < TheCall->getNumArgs(); ++i) {
+    if (!TheCall->getArg(0)->getType()->hasFloatingRepresentation())
+      return true;
+  }
+  return false;
+}
+
 // Note: returning true in this case results in CheckBuiltinFunctionCall
 // returning an ExprError
 bool Sema::CheckHLSLBuiltinFunctionCall(unsigned BuiltinID, CallExpr *TheCall) {
@@ -5225,6 +5239,17 @@ bool Sema::CheckHLSLBuiltinFunctionCall(unsigned BuiltinID, CallExpr *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 (checkAllArgsAreFloatRepresnations(TheCall))
+      return true;
+    break;
+  }
   }
   return false;
 }

clang/test/CodeGenHLSL/builtins/lerp-builtin.hlsl

@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple dxil-pc-shadermodel6.3-library %s -fnative-half-type -emit-llvm -disable-llvm-passes -o - | FileCheck %s
+
+
+
+// CHECK-LABEL: builtin_lerp_half_scalar
+// CHECK: %3 = fsub double %conv1, %conv
+// CHECK: %4 = fmul double %conv2, %3
+// CHECK: %dx.lerp = fadd double %conv, %4
+// CHECK: %conv3 = fptrunc double %dx.lerp to half
+// CHECK: ret half %conv3
+half builtin_lerp_half_scalar (half p0) {
+  return __builtin_hlsl_lerp ( p0, p0, p0 );
+}
+
+// CHECK-LABEL: builtin_lerp_float_scalar
+// CHECK: %3 = fsub double %conv1, %conv
+// CHECK: %4 = fmul double %conv2, %3
+// CHECK: %dx.lerp = fadd double %conv, %4
+// CHECK: %conv3 = fptrunc double %dx.lerp to float
+// CHECK: ret float %conv3
+float builtin_lerp_float_scalar ( float p0) {
+  return __builtin_hlsl_lerp ( p0, p0, p0 );
+}
+
+// CHECK-LABEL: builtin_lerp_half_vector
+// CHECK: %dx.lerp = call <3 x half> @llvm.dx.lerp.v3f16(<3 x half> %0, <3 x half> %1, <3 x half> %2)
+// CHECK: ret <3 x half> %dx.lerp
+half3 builtin_lerp_half_vector (half3 p0) {
+  return __builtin_hlsl_lerp ( p0, p0, p0 );
+}
+
+// CHECK-LABEL: builtin_lerp_floar_vector
+// CHECK: %dx.lerp = call <2 x float> @llvm.dx.lerp.v2f32(<2 x float> %0, <2 x float> %1, <2 x float> %2)
+// CHECK: ret <2 x float> %dx.lerp
+float2 builtin_lerp_floar_vector ( float2 p0) {
+  return __builtin_hlsl_lerp ( p0, p0, p0 );
+}

clang/test/CodeGenHLSL/builtins/lerp.hlsl

@@ -0,0 +1,105 @@
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple \
+// RUN:   dxil-pc-shadermodel6.3-library %s -fnative-half-type \
+// RUN:   -emit-llvm -disable-llvm-passes -o - | FileCheck %s \ 
+// RUN:   --check-prefixes=CHECK,NATIVE_HALF
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple \
+// RUN:   dxil-pc-shadermodel6.3-library %s -emit-llvm -disable-llvm-passes \
+// RUN:   -o - | FileCheck %s --check-prefixes=CHECK,NO_HALF
+
+// NATIVE_HALF: %3 = fsub half %1, %0
+// NATIVE_HALF: %4 = fmul half %2, %3
+// NATIVE_HALF: %dx.lerp = fadd half %0, %4
+// NATIVE_HALF: ret half %dx.lerp
+// NO_HALF: %3 = fsub float %1, %0
+// NO_HALF: %4 = fmul float %2, %3
+// NO_HALF: %dx.lerp = fadd float %0, %4
+// NO_HALF: ret float %dx.lerp
+half test_lerp_half ( half p0) {
+  return lerp ( p0, p0, p0 );
+}
+
+// NATIVE_HALF: %dx.lerp = call <2 x half> @llvm.dx.lerp.v2f16(<2 x half> %0, <2 x half> %1, <2 x half> %2)
+// NATIVE_HALF: ret <2 x half> %dx.lerp
+// NO_HALF: %dx.lerp = call <2 x float> @llvm.dx.lerp.v2f32(<2 x float> %0, <2 x float> %1, <2 x float> %2)
+// NO_HALF: ret <2 x float> %dx.lerp
+half2  test_lerp_half2 ( half2 p0, half2 p1 ) {
+  return lerp ( p0, p0, p0 );
+}
+
+// NATIVE_HALF: %dx.lerp = call <3 x half> @llvm.dx.lerp.v3f16(<3 x half> %0, <3 x half> %1, <3 x half> %2)
+// NATIVE_HALF: ret <3 x half> %dx.lerp
+// NO_HALF: %dx.lerp = call <3 x float> @llvm.dx.lerp.v3f32(<3 x float> %0, <3 x float> %1, <3 x float> %2)
+// NO_HALF: ret <3 x float> %dx.lerp
+half3  test_lerp_half3 ( half3 p0, half3 p1 ) {
+  return lerp ( p0, p0, p0 );
+}
+
+// NATIVE_HALF: %dx.lerp = call <4 x half> @llvm.dx.lerp.v4f16(<4 x half> %0, <4 x half> %1, <4 x half> %2)
+// NATIVE_HALF: ret <4 x half> %dx.lerp
+// NO_HALF: %dx.lerp = call <4 x float> @llvm.dx.lerp.v4f32(<4 x float> %0, <4 x float> %1, <4 x float> %2)
+// NO_HALF: ret <4 x float> %dx.lerp
+half4  test_lerp_half4 ( half4 p0, half4 p1 ) {
+  return lerp ( p0, p0, p0 );
+}
+
+// CHECK: %3 = fsub float %1, %0
+// CHECK: %4 = fmul float %2, %3
+// CHECK: %dx.lerp = fadd float %0, %4
+// CHECK: ret float %dx.lerp
+float  test_lerp_float ( float p0, float p1 ) {
+  return lerp ( p0, p0, p0 );
+}
+
+// CHECK: %dx.lerp = call <2 x float> @llvm.dx.lerp.v2f32(<2 x float> %0, <2 x float> %1, <2 x float> %2)
+// CHECK: ret <2 x float> %dx.lerp
+float2  test_lerp_float2 ( float2 p0, float2 p1 ) {
+  return lerp ( p0, p0, p0 );
+}
+
+// CHECK: %dx.lerp = call <3 x float> @llvm.dx.lerp.v3f32(<3 x float> %0, <3 x float> %1, <3 x float> %2)
+// CHECK: ret <3 x float> %dx.lerp
+float3  test_lerp_float3 ( float3 p0, float3 p1 ) {
+  return lerp ( p0, p0, p0 );
+}
+
+// CHECK: %dx.lerp = call <4 x float> @llvm.dx.lerp.v4f32(<4 x float> %0, <4 x float> %1, <4 x float> %2)
+// CHECK: ret <4 x float> %dx.lerp
+float4  test_lerp_float4 ( float4 p0, float4 p1) {
+  return lerp ( p0, p0, p0 );
+}
+
+// CHECK: %dx.lerp = call <2 x float> @llvm.dx.lerp.v2f32(<2 x float> %splat.splat, <2 x float> %1, <2 x float> %2)
+// CHECK: ret <2 x float> %dx.lerp
+float2  test_lerp_float2_splat ( float p0, float2 p1 ) {
+  return lerp( p0, p1, p1 );
+}
+
+// CHECK: %dx.lerp = call <3 x float> @llvm.dx.lerp.v3f32(<3 x float> %splat.splat, <3 x float> %1, <3 x float> %2)
+// CHECK: ret <3 x float> %dx.lerp
+float3  test_lerp_float3_splat ( float p0, float3 p1 ) {
+  return lerp( p0, p1, p1 );
+}
+
+// CHECK:  %dx.lerp = call <4 x float> @llvm.dx.lerp.v4f32(<4 x float> %splat.splat, <4 x float> %1, <4 x float> %2)
+// CHECK:  ret <4 x float> %dx.lerp
+float4  test_lerp_float4_splat ( float p0, float4 p1 ) {
+  return lerp( p0, p1, p1 );
+}
+
+// CHECK: %conv = sitofp i32 %2 to float
+// CHECK: %splat.splatinsert = insertelement <2 x float> poison, float %conv, i64 0
+// CHECK: %splat.splat = shufflevector <2 x float> %splat.splatinsert, <2 x float> poison, <2 x i32> zeroinitializer
+// CHECK: %dx.lerp = call <2 x float> @llvm.dx.lerp.v2f32(<2 x float> %0, <2 x float> %1, <2 x float> %splat.splat)
+// CHECK: ret <2 x float> %dx.lerp
+float2 test_lerp_float2_int_splat ( float2 p0, int p1 ) {
+  return lerp ( p0, p0, p1 );
+}
+
+// CHECK: %conv = sitofp i32 %2 to float
+// CHECK: %splat.splatinsert = insertelement <3 x float> poison, float %conv, i64 0
+// CHECK: %splat.splat = shufflevector <3 x float> %splat.splatinsert, <3 x float> poison, <3 x i32> zeroinitializer
+// CHECK:  %dx.lerp = call <3 x float> @llvm.dx.lerp.v3f32(<3 x float> %0, <3 x float> %1, <3 x float> %splat.splat)
+// CHECK: ret <3 x float> %dx.lerp
+float3 test_lerp_float3_int_splat ( float3 p0, int p1 ) {
+  return lerp ( p0, p0, p1 );
+}