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

via llvm-commits llvm-commits at lists.llvm.org
Tue Apr 15 15:57:11 PDT 2025


llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-spir-v

Author: Kaitlin Peng (kmpeng)

<details>
<summary>Changes</summary>

Resolves #<!-- -->99114. There will be a follow-up PR on pattern matching later.

Tasks completed:
- Implement `faceforward` in `hlsl_intrinsics.h`/`hlsl_intrinsic_helpers.h`
- Implement `faceforward` SPIR-V target builtin in `clang/include/clang/Basic/BuiltinsSPIRV.td`
- Add a SPIR-V fast path in `hlsl_intrinsic_helpers.h`
- Add sema checks for `faceforward` to `CheckSPIRVBuiltinFunctionCall` in `clang/lib/Sema/SemaSPIRV.cpp`
- Add codegen for SPIR-V `faceforward` builtin to `EmitSPIRVBuiltinExpr` in `SPIR.cpp`
- Add HLSL codegen tests to `clang/test/CodeGenHLSL/builtins/faceforward.hlsl`
- Add SPIRV builtin codegen tests to `clang/test/CodeGenSPIRV/Builtins/faceforward.c`
- Add sema tests to `clang/test/SemaHLSL/BuiltIns/faceforward-errors.hlsl`
- Add spirv sema tests to `clang/test/SemaSPIRV/BuiltIns/faceforward-errors.c`
- Create the `int_spv_faceforward` intrinsic in `IntrinsicsSPIRV.td`
- In `SPIRVInstructionSelector.cpp` create the `faceforward` lowering and map it to `int_spv_faceforward` in `SPIRVInstructionSelector::selectIntrinsic`
- Create SPIR-V backend test case in `llvm/test/CodeGen/SPIRV/hlsl-intrinsics/faceforward.ll`

Incomplete tasks:
- Create SPIR-V backend test case in `llvm/test/CodeGen/SPIRV/opencl/faceforward.ll`
  - Not applicable because the OpenCL SPIR-V extended instruction set does not include a `faceforward` function

---

Patch is 27.53 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/135878.diff


12 Files Affected:

- (modified) clang/include/clang/Basic/BuiltinsSPIRV.td (+6) 
- (modified) clang/lib/CodeGen/TargetBuiltins/SPIR.cpp (+12) 
- (modified) clang/lib/Headers/hlsl/hlsl_intrinsic_helpers.h (+18) 
- (modified) clang/lib/Headers/hlsl/hlsl_intrinsics.h (+47) 
- (modified) clang/lib/Sema/SemaSPIRV.cpp (+36) 
- (added) clang/test/CodeGenHLSL/builtins/faceforward.hlsl (+94) 
- (added) clang/test/CodeGenSPIRV/Builtins/faceforward.c (+35) 
- (added) clang/test/SemaHLSL/BuiltIns/faceforward-errors.hlsl (+39) 
- (added) clang/test/SemaSPIRV/BuiltIns/faceforward-errors.c (+54) 
- (modified) llvm/include/llvm/IR/IntrinsicsSPIRV.td (+1) 
- (modified) llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp (+2) 
- (added) llvm/test/CodeGen/SPIRV/hlsl-intrinsics/faceforward.ll (+60) 


``````````diff
diff --git a/clang/include/clang/Basic/BuiltinsSPIRV.td b/clang/include/clang/Basic/BuiltinsSPIRV.td
index 9f76d672cc7ce..cc0c2f960f8d2 100644
--- a/clang/include/clang/Basic/BuiltinsSPIRV.td
+++ b/clang/include/clang/Basic/BuiltinsSPIRV.td
@@ -31,3 +31,9 @@ def SPIRVSmoothStep : Builtin {
   let Attributes = [NoThrow, Const, CustomTypeChecking];
   let Prototype = "void(...)";
 }
+
+def SPIRVFaceForward : Builtin {
+  let Spellings = ["__builtin_spirv_faceforward"];
+  let Attributes = [NoThrow, Const, CustomTypeChecking];
+  let Prototype = "void(...)";
+}
diff --git a/clang/lib/CodeGen/TargetBuiltins/SPIR.cpp b/clang/lib/CodeGen/TargetBuiltins/SPIR.cpp
index 92e2c1c6da68f..c1bcc9ae084d0 100644
--- a/clang/lib/CodeGen/TargetBuiltins/SPIR.cpp
+++ b/clang/lib/CodeGen/TargetBuiltins/SPIR.cpp
@@ -71,6 +71,18 @@ Value *CodeGenFunction::EmitSPIRVBuiltinExpr(unsigned BuiltinID,
         ArrayRef<Value *>{Min, Max, X}, /*FMFSource=*/nullptr,
         "spv.smoothstep");
   }
+  case SPIRV::BI__builtin_spirv_faceforward: {
+    Value *N = EmitScalarExpr(E->getArg(0));
+    Value *I = EmitScalarExpr(E->getArg(1));
+    Value *Ng = EmitScalarExpr(E->getArg(2));
+    assert(E->getArg(0)->getType()->hasFloatingRepresentation() &&
+           E->getArg(1)->getType()->hasFloatingRepresentation() &&
+           E->getArg(2)->getType()->hasFloatingRepresentation() &&
+           "FaceForward operands must have a float representation");
+    return Builder.CreateIntrinsic(
+        /*ReturnType=*/N->getType(), Intrinsic::spv_smoothstep,
+        ArrayRef<Value *>{N, I, Ng}, /*FMFSource=*/nullptr, "spv.faceforward");
+  }
   }
   return nullptr;
 }
diff --git a/clang/lib/Headers/hlsl/hlsl_intrinsic_helpers.h b/clang/lib/Headers/hlsl/hlsl_intrinsic_helpers.h
index 3a8a9b6fa2a45..b2332419dc034 100644
--- a/clang/lib/Headers/hlsl/hlsl_intrinsic_helpers.h
+++ b/clang/lib/Headers/hlsl/hlsl_intrinsic_helpers.h
@@ -126,6 +126,24 @@ template <typename T> constexpr vector<T, 4> lit_impl(T NDotL, T NDotH, T M) {
   return Result;
 }
 
+template <typename T> constexpr T faceforward_impl(T N, T I, T Ng) {
+#if (__has_builtin(__builtin_spirv_faceforward))
+  return __builtin_spirv_faceforward(N, I, Ng);
+#else
+  return select(I * Ng < 0, N, -N);
+#endif
+}
+
+template <typename T, int L>
+constexpr vector<T, L> faceforward_vec_impl(vector<T, L> N, vector<T, L> I,
+                                            vector<T, L> Ng) {
+#if (__has_builtin(__builtin_spirv_faceforward))
+  return __builtin_spirv_faceforward(N, I, Ng);
+#else
+  return select(dot(I, Ng) < 0, N, -N);
+#endif
+}
+
 } // namespace __detail
 } // namespace hlsl
 
diff --git a/clang/lib/Headers/hlsl/hlsl_intrinsics.h b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
index 35ff80052cf43..f4af34ea28b86 100644
--- a/clang/lib/Headers/hlsl/hlsl_intrinsics.h
+++ b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
@@ -214,6 +214,53 @@ const inline double4 dst(double4 Src0, double4 Src1) {
   return __detail::dst_impl(Src0, Src1);
 }
 
+//===----------------------------------------------------------------------===//
+// faceforward builtin
+//===----------------------------------------------------------------------===//
+
+/// \fn T faceforward(T N, T I, T Ng)
+/// \brief Flips the surface-normal (if needed) to face in a direction opposite
+/// to \a I. Returns the result in \a N.
+/// \param N The resulting floating-point surface-normal vector.
+/// \param I A floating-point, incident vector that points from the view
+/// position to the shading position.
+/// \param Ng A floating-point surface-normal vector.
+///
+/// Return a floating-point, surface normal vector that is facing the view
+/// direction.
+
+template <typename T>
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+const inline __detail::enable_if_t<__detail::is_arithmetic<T>::Value &&
+                                       __detail::is_same<half, T>::value,
+                                   T> faceforward(T N, T I, T Ng) {
+  return __detail::faceforward_impl(N, I, Ng);
+}
+
+template <typename T>
+const inline __detail::enable_if_t<
+    __detail::is_arithmetic<T>::Value && __detail::is_same<float, T>::value, T>
+faceforward(T N, T I, T Ng) {
+  return __detail::faceforward_impl(N, I, Ng);
+}
+
+template <int L>
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+const inline __detail::HLSL_FIXED_VECTOR<half, L> faceforward(
+    __detail::HLSL_FIXED_VECTOR<half, L> N,
+    __detail::HLSL_FIXED_VECTOR<half, L> I,
+    __detail::HLSL_FIXED_VECTOR<half, L> Ng) {
+  return __detail::faceforward_vec_impl(N, I, Ng);
+}
+
+template <int L>
+const inline __detail::HLSL_FIXED_VECTOR<float, L>
+faceforward(__detail::HLSL_FIXED_VECTOR<float, L> N,
+            __detail::HLSL_FIXED_VECTOR<float, L> I,
+            __detail::HLSL_FIXED_VECTOR<float, L> Ng) {
+  return __detail::faceforward_vec_impl(N, I, Ng);
+}
+
 //===----------------------------------------------------------------------===//
 // fmod builtins
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/Sema/SemaSPIRV.cpp b/clang/lib/Sema/SemaSPIRV.cpp
index 7131514d53421..ed40d005c8ce5 100644
--- a/clang/lib/Sema/SemaSPIRV.cpp
+++ b/clang/lib/Sema/SemaSPIRV.cpp
@@ -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(),
+                                                         B.get()->getType()) &&
+          SemaRef.getASTContext().hasSameUnqualifiedType(A.get()->getType(),
+                                                         C.get()->getType()))) {
+      SemaRef.Diag(TheCall->getBeginLoc(),
+                   diag::err_vec_builtin_incompatible_vector)
+          << TheCall->getDirectCallee() << /*useAllTerminology*/ true
+          << SourceRange(A.get()->getBeginLoc(), C.get()->getEndLoc());
+      return true;
+    }
+
+    QualType RetTy = A.get()->getType();
+    TheCall->setType(RetTy);
+    break;
+  }
   }
   return false;
 }
diff --git a/clang/test/CodeGenHLSL/builtins/faceforward.hlsl b/clang/test/CodeGenHLSL/builtins/faceforward.hlsl
new file mode 100644
index 0000000000000..d1942a4bc4b6c
--- /dev/null
+++ b/clang/test/CodeGenHLSL/builtins/faceforward.hlsl
@@ -0,0 +1,94 @@
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple \
+// RUN:   dxil-pc-shadermodel6.3-library %s -fnative-half-type \
+// RUN:   -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -finclude-default-header -triple \
+// RUN:   spirv-unknown-vulkan-compute %s -fnative-half-type \
+// RUN:   -emit-llvm -o - | FileCheck %s --check-prefix=SPVCHECK
+
+// CHECK-LABEL: test_faceforward_half
+// CHECK: %mul.i = fmul reassoc nnan ninf nsz arcp afn half %{{.*}}, %{{.*}}
+// CHECK: %cmp.i = fcmp reassoc nnan ninf nsz arcp afn olt half %mul.i, 0xH0000
+// CHECK: %fneg.i = fneg reassoc nnan ninf nsz arcp afn half %{{.*}}
+// CHECK: %hlsl.select.i = select reassoc nnan ninf nsz arcp afn i1 %cmp.i, half %{{.*}}, half %fneg.i
+// CHECK: ret half %hlsl.select.i
+// SPVCHECK-LABEL: test_faceforward_half
+// SPVCHECK: %spv.faceforward.i = call reassoc nnan ninf nsz arcp afn noundef half @llvm.spv.smoothstep.f16(half %{{.*}}, half %{{.*}}, half %{{.*}})
+// SPVCHECK: ret half %spv.faceforward.i
+half test_faceforward_half(half N, half I, half Ng) { return faceforward(N, I, Ng); }
+
+// CHECK-LABEL: test_faceforward_half2
+// CHECK: %hlsl.dot.i = call reassoc nnan ninf nsz arcp afn half @llvm.dx.fdot.v2f16(<2 x half> %{{.*}}, <2 x half> %{{.*}})
+// CHECK: %cmp.i = fcmp reassoc nnan ninf nsz arcp afn olt half %hlsl.dot.i, 0xH0000
+// CHECK: %fneg.i = fneg reassoc nnan ninf nsz arcp afn <2 x half> %{{.*}}
+// CHECK: %hlsl.select.i = select reassoc nnan ninf nsz arcp afn i1 %cmp.i, <2 x half> %{{.*}}, <2 x half> %fneg.i
+// CHECK: ret <2 x half> %hlsl.select.i
+// SPVCHECK-LABEL: test_faceforward_half2
+// SPVCHECK: %spv.faceforward.i = call reassoc nnan ninf nsz arcp afn noundef <2 x half> @llvm.spv.smoothstep.v2f16(<2 x half> %{{.*}}, <2 x half> %{{.*}}, <2 x half> %{{.*}})
+// SPVCHECK: ret <2 x half> %spv.faceforward.i
+half2 test_faceforward_half2(half2 N, half2 I, half2 Ng) { return faceforward(N, I, Ng); }
+
+// CHECK-LABEL: test_faceforward_half3
+// CHECK: %hlsl.dot.i = call reassoc nnan ninf nsz arcp afn half @llvm.dx.fdot.v3f16(<3 x half> %{{.*}}, <3 x half> %{{.*}})
+// CHECK: %cmp.i = fcmp reassoc nnan ninf nsz arcp afn olt half %hlsl.dot.i, 0xH0000
+// CHECK: %fneg.i = fneg reassoc nnan ninf nsz arcp afn <3 x half> %{{.*}}
+// CHECK: %hlsl.select.i = select reassoc nnan ninf nsz arcp afn i1 %cmp.i, <3 x half> %{{.*}}, <3 x half> %fneg.i
+// CHECK: ret <3 x half> %hlsl.select.i
+// SPVCHECK-LABEL: test_faceforward_half3
+// SPVCHECK: %spv.faceforward.i = call reassoc nnan ninf nsz arcp afn noundef <3 x half> @llvm.spv.smoothstep.v3f16(<3 x half> %{{.*}}, <3 x half> %{{.*}}, <3 x half> %{{.*}})
+// SPVCHECK: ret <3 x half> %spv.faceforward.i
+half3 test_faceforward_half3(half3 N, half3 I, half3 Ng) { return faceforward(N, I, Ng); }
+
+// CHECK-LABEL: test_faceforward_half4
+// CHECK: %hlsl.dot.i = call reassoc nnan ninf nsz arcp afn half @llvm.dx.fdot.v4f16(<4 x half> %{{.*}}, <4 x half> %{{.*}})
+// CHECK: %cmp.i = fcmp reassoc nnan ninf nsz arcp afn olt half %hlsl.dot.i, 0xH0000
+// CHECK: %fneg.i = fneg reassoc nnan ninf nsz arcp afn <4 x half> %{{.*}}
+// CHECK: %hlsl.select.i = select reassoc nnan ninf nsz arcp afn i1 %cmp.i, <4 x half> %{{.*}}, <4 x half> %fneg.i
+// CHECK: ret <4 x half> %hlsl.select.i
+// SPVCHECK-LABEL: test_faceforward_half4
+// SPVCHECK: %spv.faceforward.i = call reassoc nnan ninf nsz arcp afn noundef <4 x half> @llvm.spv.smoothstep.v4f16(<4 x half> %{{.*}}, <4 x half> %{{.*}}, <4 x half> %{{.*}})
+// SPVCHECK: ret <4 x half> %spv.faceforward.i
+half4 test_faceforward_half4(half4 N, half4 I, half4 Ng) { return faceforward(N, I, Ng); }
+
+// CHECK-LABEL: test_faceforward_float
+// CHECK: %mul.i = fmul reassoc nnan ninf nsz arcp afn float %{{.*}}, %{{.*}}
+// CHECK: %cmp.i = fcmp reassoc nnan ninf nsz arcp afn olt float %mul.i, 0.000000e+00
+// CHECK: %fneg.i = fneg reassoc nnan ninf nsz arcp afn float %{{.*}}
+// CHECK: %hlsl.select.i = select reassoc nnan ninf nsz arcp afn i1 %cmp.i, float %{{.*}}, float %fneg.i
+// CHECK: ret float %hlsl.select.i
+// SPVCHECK-LABEL: test_faceforward_float
+// SPVCHECK: %spv.faceforward.i = call reassoc nnan ninf nsz arcp afn noundef float @llvm.spv.smoothstep.f32(float %{{.*}}, float %{{.*}}, float %{{.*}})
+// SPVCHECK: ret float %spv.faceforward.i
+float test_faceforward_float(float N, float I, float Ng) { return faceforward(N, I, Ng); }
+
+// CHECK-LABEL: test_faceforward_float2
+// CHECK: %hlsl.dot.i = call reassoc nnan ninf nsz arcp afn float @llvm.dx.fdot.v2f32(<2 x float> %{{.*}}, <2 x float> %{{.*}})
+// CHECK: %cmp.i = fcmp reassoc nnan ninf nsz arcp afn olt float %hlsl.dot.i, 0.000000e+00
+// CHECK: %fneg.i = fneg reassoc nnan ninf nsz arcp afn <2 x float> %{{.*}}
+// CHECK: %hlsl.select.i = select reassoc nnan ninf nsz arcp afn i1 %cmp.i, <2 x float> %{{.*}}, <2 x float> %fneg.i
+// CHECK: ret <2 x float> %hlsl.select.i
+// SPVCHECK-LABEL: test_faceforward_float2
+// SPVCHECK: %spv.faceforward.i = call reassoc nnan ninf nsz arcp afn noundef <2 x float> @llvm.spv.smoothstep.v2f32(<2 x float> %{{.*}}, <2 x float> %{{.*}}, <2 x float> %{{.*}})
+// SPVCHECK: ret <2 x float> %spv.faceforward.i
+float2 test_faceforward_float2(float2 N, float2 I, float2 Ng) { return faceforward(N, I, Ng); }
+
+// CHECK-LABEL: test_faceforward_float3
+// CHECK: %hlsl.dot.i = call reassoc nnan ninf nsz arcp afn float @llvm.dx.fdot.v3f32(<3 x float> %{{.*}}, <3 x float> %{{.*}})
+// CHECK: %cmp.i = fcmp reassoc nnan ninf nsz arcp afn olt float %hlsl.dot.i, 0.000000e+00
+// CHECK: %fneg.i = fneg reassoc nnan ninf nsz arcp afn <3 x float> %{{.*}}
+// CHECK: %hlsl.select.i = select reassoc nnan ninf nsz arcp afn i1 %cmp.i, <3 x float> %{{.*}}, <3 x float> %fneg.i
+// CHECK: ret <3 x float> %hlsl.select.i
+// SPVCHECK-LABEL: test_faceforward_float3
+// SPVCHECK: %spv.faceforward.i = call reassoc nnan ninf nsz arcp afn noundef <3 x float> @llvm.spv.smoothstep.v3f32(<3 x float> %{{.*}}, <3 x float> %{{.*}}, <3 x float> %{{.*}})
+// SPVCHECK: ret <3 x float> %spv.faceforward.i
+float3 test_faceforward_float3(float3 N, float3 I, float3 Ng) { return faceforward(N, I, Ng); }
+
+// CHECK-LABEL: test_faceforward_float4
+// CHECK: %hlsl.dot.i = call reassoc nnan ninf nsz arcp afn float @llvm.dx.fdot.v4f32(<4 x float> %{{.*}}, <4 x float> %{{.*}})
+// CHECK: %cmp.i = fcmp reassoc nnan ninf nsz arcp afn olt float %hlsl.dot.i, 0.000000e+00
+// CHECK: %fneg.i = fneg reassoc nnan ninf nsz arcp afn <4 x float> %{{.*}}
+// CHECK: %hlsl.select.i = select reassoc nnan ninf nsz arcp afn i1 %cmp.i, <4 x float> %{{.*}}, <4 x float> %fneg.i
+// CHECK: ret <4 x float> %hlsl.select.i
+// SPVCHECK-LABEL: test_faceforward_float4
+// SPVCHECK: %spv.faceforward.i = call reassoc nnan ninf nsz arcp afn noundef <4 x float> @llvm.spv.smoothstep.v4f32(<4 x float> %{{.*}}, <4 x float> %{{.*}}, <4 x float> %{{.*}})
+// SPVCHECK: ret <4 x float> %spv.faceforward.i
+float4 test_faceforward_float4(float4 N, float4 I, float4 Ng) { return faceforward(N, I, Ng); }
diff --git a/clang/test/CodeGenSPIRV/Builtins/faceforward.c b/clang/test/CodeGenSPIRV/Builtins/faceforward.c
new file mode 100644
index 0000000000000..17e3268aab9ef
--- /dev/null
+++ b/clang/test/CodeGenSPIRV/Builtins/faceforward.c
@@ -0,0 +1,35 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 5
+
+// RUN: %clang_cc1 -O1 -triple spirv-pc-vulkan-compute %s -emit-llvm -o - | FileCheck %s
+
+typedef float float2 __attribute__((ext_vector_type(2)));
+typedef float float3 __attribute__((ext_vector_type(3)));
+typedef float float4 __attribute__((ext_vector_type(4)));
+
+// CHECK-LABEL: define spir_func float @test_faceforward_float(
+// CHECK-SAME: float noundef [[N:%.*]], float noundef [[I:%.*]], float noundef [[NG:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[SPV_FACEFORWARD:%.*]] = tail call float @llvm.spv.smoothstep.f32(float [[N]], float [[I]], float [[NG]])
+// CHECK-NEXT:    ret float [[SPV_FACEFORWARD]]
+float test_faceforward_float(float N, float I, float Ng) { return __builtin_spirv_faceforward(N, I, Ng); }
+
+// CHECK-LABEL: define spir_func <2 x float> @test_faceforward_float2(
+// CHECK-SAME: <2 x float> noundef [[N:%.*]], <2 x float> noundef [[I:%.*]], <2 x float> noundef [[NG:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[SPV_FACEFORWARD:%.*]] = tail call <2 x float> @llvm.spv.smoothstep.v2f32(<2 x float> [[N]], <2 x float> [[I]], <2 x float> [[NG]])
+// CHECK-NEXT:    ret <2 x float> [[SPV_FACEFORWARD]]
+float2 test_faceforward_float2(float2 N, float2 I, float2 Ng) { return __builtin_spirv_faceforward(N, I, Ng); }
+
+// CHECK-LABEL: define spir_func <3 x float> @test_faceforward_float3(
+// CHECK-SAME: <3 x float> noundef [[N:%.*]], <3 x float> noundef [[I:%.*]], <3 x float> noundef [[NG:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[SPV_FACEFORWARD:%.*]] = tail call <3 x float> @llvm.spv.smoothstep.v3f32(<3 x float> [[N]], <3 x float> [[I]], <3 x float> [[NG]])
+// CHECK-NEXT:    ret <3 x float> [[SPV_FACEFORWARD]]
+float3 test_faceforward_float3(float3 N, float3 I, float3 Ng) { return __builtin_spirv_faceforward(N, I, Ng); }
+
+// CHECK-LABEL: define spir_func <4 x float> @test_faceforward_float4(
+// CHECK-SAME: <4 x float> noundef [[N:%.*]], <4 x float> noundef [[I:%.*]], <4 x float> noundef [[NG:%.*]]) local_unnamed_addr #[[ATTR0]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[SPV_FACEFORWARD:%.*]] = tail call <4 x float> @llvm.spv.smoothstep.v4f32(<4 x float> [[N]], <4 x float> [[I]], <4 x float> [[NG]])
+// CHECK-NEXT:    ret <4 x float> [[SPV_FACEFORWARD]]
+float4 test_faceforward_float4(float4 N, float4 I, float4 Ng) { return __builtin_spirv_faceforward(N, I, Ng); }
diff --git a/clang/test/SemaHLSL/BuiltIns/faceforward-errors.hlsl b/clang/test/SemaHLSL/BuiltIns/faceforward-errors.hlsl
new file mode 100644
index 0000000000000..469d55995f966
--- /dev/null
+++ b/clang/test/SemaHLSL/BuiltIns/faceforward-errors.hlsl
@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.6-library %s -fnative-half-type -emit-llvm-only -disable-llvm-passes -verify
+
+float test_double_inputs(double p0, double p1, double p2) {
+  return faceforward(p0, p1, p2);
+  // expected-error at -1  {{no matching function for call to 'faceforward'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored}}
+}
+
+float test_int_inputs(int p0, int p1, int p2) {
+  return faceforward(p0, p1, p2);
+  // expected-error at -1  {{no matching function for call to 'faceforward'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored}}
+}
+
+float1 test_vec1_inputs(float1 p0, float1 p1, float1 p2) {
+  return faceforward(p0, p1, p2);
+  // expected-error at -1  {{no matching function for call to 'faceforward'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored: substitution failure [with T = float1]: no type named 'Type' in 'hlsl::__detail::enable_if<false, vector<float, 1>>'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored: substitution failure [with T = float1]: no type named 'Type' in 'hlsl::__detail::enable_if<false, vector<float, 1>>'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored: substitution failure [with L = 1]: no type named 'Type' in 'hlsl::__detail::enable_if<false, half>'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored: substitution failure [with L = 1]: no type named 'Type' in 'hlsl::__detail::enable_if<false, float>'}}
+}
+
+typedef float float5 __attribute__((ext_vector_type(5)));
+
+float5 test_vec5_inputs(float5 p0, float5 p1, float5 p2) {
+  return faceforward(p0, p1, p2);
+  // expected-error at -1  {{no matching function for call to 'faceforward'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored: substitution failure [with T = float5]: no type named 'Type' in 'hlsl::__detail::enable_if<false, vector<float, 5>>'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored: substitution failure [with T = float5]: no type named 'Type' in 'hlsl::__detail::enable_if<false, vector<float, 5>>'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored: substitution failure [with L = 5]: no type named 'Type' in 'hlsl::__detail::enable_if<false, half>'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate template ignored: substitution failure [with L = 5]: no type named 'Type' in 'hlsl::__detail::enable_if<false, float>'}}
+}
diff --git a/clang/test/SemaSPIRV/BuiltIns/faceforward-errors.c b/clang/test/SemaSPIRV/BuiltIns/faceforward-errors.c
new file mode 100644
index 0000000000000..28089709e6bd5
--- /dev/null
+++ b/clang/test/SemaSPIRV/BuiltIns/faceforward-errors.c
@@ -0,0...
[truncated]

``````````

</details>


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


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