[clang] Implementing `asfloat` using `bit_cast` (PR #108686)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-hlsl

@llvm/pr-subscribers-clang

Author: None (joaosaffran)

<details>
<summary>Changes</summary>

This PR is implementing `asfloat` for HLSL.

Fixes: #<!-- -->70098

---
Full diff: https://github.com/llvm/llvm-project/pull/108686.diff


3 Files Affected:

- (modified) clang/lib/Headers/hlsl/hlsl_intrinsics.h (+17) 
- (added) clang/test/CodeGenHLSL/builtins/asfloat.hlsl (+40) 
- (added) clang/test/SemaHLSL/BuiltIns/asfloat-errors.hlsl (+35) 


``````````diff
diff --git a/clang/lib/Headers/hlsl/hlsl_intrinsics.h b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
index b5c22f7c91b2d6..cb8e1119e9b4e8 100644
--- a/clang/lib/Headers/hlsl/hlsl_intrinsics.h
+++ b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
@@ -361,6 +361,23 @@ bool any(double3);
 _HLSL_BUILTIN_ALIAS(__builtin_hlsl_any)
 bool any(double4);
 
+//===----------------------------------------------------------------------===//
+// asfloat builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn uint asfloat(T Val)
+/// \brief Interprets the bit pattern of x as an unsigned integer.
+/// \param Val The input value.
+
+template <typename T, int N>
+_HLSL_INLINE 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) {
+  return __detail::bit_cast<float, T>(F);
+}
+
 //===----------------------------------------------------------------------===//
 // asin builtins
 //===----------------------------------------------------------------------===//
diff --git a/clang/test/CodeGenHLSL/builtins/asfloat.hlsl b/clang/test/CodeGenHLSL/builtins/asfloat.hlsl
new file mode 100644
index 00000000000000..59fc15fa60b1e5
--- /dev/null
+++ b/clang/test/CodeGenHLSL/builtins/asfloat.hlsl
@@ -0,0 +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: bitcast i32 [[VAL]] to float
+float test_uint(uint p0) {
+  return asfloat(p0);
+}
+
+// CHECK: define {{.*}}test_int{{.*}}(i32 {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: bitcast i32 [[VAL]] to float
+float test_int(int p0) {
+  return asfloat(p0);
+}
+
+// CHECK: define {{.*}}test_float{{.*}}(float {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK-NOT: bitcast
+// CHECK: ret float [[VAL]]
+float test_float(float p0) {
+  return asfloat(p0);
+}
+
+// CHECK: define {{.*}}test_vector_uint{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: bitcast <4 x i32> [[VAL]] to <4 x float>
+
+float4 test_vector_uint(uint4 p0) {
+  return asfloat(p0);
+}
+
+// CHECK: define {{.*}}test_vector_int{{.*}}(<4 x i32> {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK: bitcast <4 x i32> [[VAL]] to <4 x float>
+float4 test_vector_int(int4 p0) {
+  return asfloat(p0);
+}
+
+// CHECK: define {{.*}}test_vector_float{{.*}}(<4 x float> {{.*}} [[VAL:%.*]]){{.*}} 
+// CHECK-NOT: bitcast
+// CHECK: ret <4 x float> [[VAL]]
+float4 test_vector_float(float4 p0) {
+  return asfloat(p0);
+}
diff --git a/clang/test/SemaHLSL/BuiltIns/asfloat-errors.hlsl b/clang/test/SemaHLSL/BuiltIns/asfloat-errors.hlsl
new file mode 100644
index 00000000000000..16273a513c41e6
--- /dev/null
+++ b/clang/test/SemaHLSL/BuiltIns/asfloat-errors.hlsl
@@ -0,0 +1,35 @@
+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.6-library %s -fnative-half-type -verify
+
+
+float4 test_float_too_many_arg(float p0, float p1) {
+  return asfloat(p0, p1);
+  // expected-error at -1 {{no matching function for call to 'asfloat'}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate function template not viable: requires single argument 'V', but 2 arguments were provided}}
+  // expected-note at hlsl/hlsl_intrinsics.h:* {{candidate function template not viable: requires single argument 'F', but 2 arguments were provided}}
+}
+
+
+float test_float_double(double p1) {
+    return asfloat(p1);
+    // expected-error at hlsl/hlsl_intrinsics.h:* {{no matching function for call to 'bit_cast'}}
+    // expected-note at -2 {{in instantiation of function template specialization 'hlsl::asfloat<double>'}}
+    // expected-note at hlsl/hlsl_detail.h:* {{candidate template ignored: could not match 'vector<double, N>' against 'double'}}
+    // expected-note at hlsl/hlsl_detail.h:* {{candidate template ignored: substitution failure [with U = float, T = double]: no type named 'Type'}}
+}
+
+float test_float_half(half p1) {
+    return asfloat(p1);
+    // expected-error at hlsl/hlsl_intrinsics.h:* {{no matching function for call to 'bit_cast'}}
+    // expected-note at -2 {{in instantiation of function template specialization 'hlsl::asfloat<half>'}}
+    // expected-note at hlsl/hlsl_detail.h:* {{candidate template ignored: could not match 'vector<half, N>' against 'half'}}
+    // expected-note at hlsl/hlsl_detail.h:* {{candidate template ignored: substitution failure [with U = float, T = half]: no type named 'Type'}}
+}
+
+
+float test_float_half(bool p1) {
+    return asfloat(p1);
+    // expected-error at hlsl/hlsl_intrinsics.h:* {{no matching function for call to 'bit_cast'}}
+    // expected-note at -2 {{in instantiation of function template specialization 'hlsl::asfloat<bool>'}}
+    // expected-note at hlsl/hlsl_detail.h:* {{candidate template ignored: could not match 'vector<bool, N>' against 'bool'}}
+    // expected-note at hlsl/hlsl_detail.h:* {{candidate template ignored: substitution failure [with U = float, T = bool]: no type named 'Type'}}
+}
\ No newline at end of file

``````````

</details>


https://github.com/llvm/llvm-project/pull/108686