[HLSL] Make casting functions constexpr (#108902)

This marks the `bit_cast` helper as `constexpr` and allows the casts
implemented with it to also be `constexpr`. This is largely not a
functional change, but it enables using the casts in expressions that
need to be resolved at compile time as demonstrated with the static
asserts in the new tests.

---------

Co-authored-by: joaosaffran <[email protected]>

Author: llvm-beanz

clang/lib/Headers/hlsl/hlsl_detail.h

@@ -13,23 +13,23 @@ namespace hlsl {
 
 namespace __detail {
 
-#define _HLSL_INLINE                                                           \
-  __attribute__((__always_inline__, __nodebug__)) static inline
-
 template <bool B, typename T> struct enable_if {};
 
 template <typename T> struct enable_if<true, T> {
   using Type = T;
 };
 
+template <bool B, class T = void>
+using enable_if_t = typename enable_if<B, T>::Type;
+
 template <typename U, typename T, int N>
-_HLSL_INLINE typename enable_if<sizeof(U) == sizeof(T), vector<U, N> >::Type
+constexpr enable_if_t<sizeof(U) == sizeof(T), vector<U, N>>
 bit_cast(vector<T, N> V) {
   return __builtin_bit_cast(vector<U, N>, V);
 }
 
 template <typename U, typename T>
-_HLSL_INLINE typename enable_if<sizeof(U) == sizeof(T), U>::Type bit_cast(T F) {
+constexpr enable_if_t<sizeof(U) == sizeof(T), U> bit_cast(T F) {
   return __builtin_bit_cast(U, F);
 }
 

clang/lib/Headers/hlsl/hlsl_intrinsics.h

@@ -370,11 +370,11 @@ bool any(double4);
 /// \param Val The input value.
 
 template <typename T, int N>
-_HLSL_INLINE vector<float, N> asfloat(vector<T, N> V) {
+constexpr vector<float, N> asfloat(vector<T, N> V) {
   return __detail::bit_cast<float, T, N>(V);
 }
 
-template <typename T> _HLSL_INLINE float asfloat(T F) {
+template <typename T> constexpr float asfloat(T F) {
   return __detail::bit_cast<float, T>(F);
 }
 
@@ -414,12 +414,11 @@ float4 asin(float4);
 /// \brief Interprets the bit pattern of x as an unsigned integer.
 /// \param Val The input value.
 
-template <typename T, int N>
-_HLSL_INLINE vector<uint, N> asuint(vector<T, N> V) {
+template <typename T, int N> constexpr vector<uint, N> asuint(vector<T, N> V) {
   return __detail::bit_cast<uint, T, N>(V);
 }
 
-template <typename T> _HLSL_INLINE uint asuint(T F) {
+template <typename T> constexpr uint asuint(T F) {
   return __detail::bit_cast<uint, T>(F);
 }
 

clang/test/CodeGenHLSL/builtins/asuint.hlsl

@@ -1,40 +1,40 @@
 // RUN: %clang_cc1 -finclude-default-header -x hlsl -triple dxil-pc-shadermodel6.3-library %s -fnative-half-type -emit-llvm -O1 -o - | FileCheck %s
 
-// CHECK: define {{.*}}test_uint{{.*}}(i32 {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_uint{{.*}}(i32 {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK-NOT: bitcast
 // CHECK: ret i32 [[VAL]]
 uint test_uint(uint p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_int{{.*}}(i32 {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_int{{.*}}(i32 {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK-NOT: bitcast
 // CHECK: ret i32 [[VAL]]
 uint test_int(int p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_float{{.*}}(float {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_float{{.*}}(float {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK: bitcast float [[VAL]] to i32
 uint test_float(float p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_vector_uint{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_vector_uint{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK-NOT: bitcast
 // CHECK: ret <4 x i32> [[VAL]]
 uint4 test_vector_uint(uint4 p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_vector_int{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_vector_int{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK-NOT: bitcast
 // CHECK: ret <4 x i32> [[VAL]]
 uint4 test_vector_int(int4 p0) {
   return asuint(p0);
 }
 
-// CHECK: define {{.*}}test_vector_float{{.*}}(<4 x float> {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: define {{.*}}test_vector_float{{.*}}(<4 x float> {{.*}} [[VAL:%.*]]){{.*}}
 // CHECK: bitcast <4 x float> [[VAL]] to <4 x i32>
 uint4 test_vector_float(float4 p0) {
   return asuint(p0);

clang/test/SemaHLSL/BuiltIns/asfloat-constexpr.hlsl

@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.6-library %s -verify
+
+// expected-no-diagnostics
+
+// Because asfloat should be constant evaluated, all the static asserts below
+// should work!
+void ConstExprTest() {
+  static_assert(asfloat(0x3f800000) == 1.0f, "One");
+  static_assert(asfloat(0x40000000.xxx).y == 2.0f, "Two");
+}

clang/test/SemaHLSL/BuiltIns/asuint-constexpr.hlsl

@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.6-library %s -verify
+
+// expected-no-diagnostics
+
+// Because asuint should be constant evaluated, all the static asserts below
+// should work!
+void ConstExprTest() {
+  static_assert(asuint(1) == 1u, "One");
+  static_assert(asuint(2.xxx).y == 2u, "Two");
+}