[HLSL] implement the rcp intrinsic

[farzonl]

This PR implements the frontend for #70100
This PR is part 1 of 2.
Part 2 requires an intrinsic to instructions lowering.

• Builtins.td - add an rcp builtin
• CGBuiltin.cpp - add the builtin to intrinsic lowering
• hlsl_intrinsics.h - add the rcp api
• SemaChecking.cpp - reuse frac's sema checks
• IntrinsicsDirectX.td - add the llvm intrinsic

[llvmbot]

@llvm/pr-subscribers-backend-directx
@llvm/pr-subscribers-llvm-ir
@llvm/pr-subscribers-clang-codegen
@llvm/pr-subscribers-backend-x86
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@llvm/pr-subscribers-clang

Author: Farzon Lotfi (farzonl)

Changes

This PR implements the frontend for llvm#70100
This PR is part 1 of 2.
Part 2 depends on DXILIntrinsicExpansion.cpp in dixl-lerp-intrinsic-lowering PR
which will have an intrinsic to instruction expansion pass.
That pass is what we need to complete the DXIL lowering portion of this PR:

• Builtins.td - add an rcp builtin
• CGBuiltin.cpp - add the builtin to intrinsic lowering
• hlsl_intrinsics.h - add the rcp api
• SemaChecking.cpp - reuse frac's sema checks
• IntrinsicsDirectX.td - add the llvm intrinsic

---

Full diff: https://github.com/llvm/llvm-project/pull/83857.diff

7 Files Affected:

• (modified) clang/include/clang/Basic/Builtins.td (+6)
• (modified) clang/lib/CodeGen/CGBuiltin.cpp (+8)
• (modified) clang/lib/Headers/hlsl/hlsl_intrinsics.h (+41)
• (modified) clang/lib/Sema/SemaChecking.cpp (+1)
• (added) clang/test/CodeGenHLSL/builtins/rcp.hlsl (+53)
• (added) clang/test/SemaHLSL/BuiltIns/rcp-errors.hlsl (+27)
• (modified) llvm/include/llvm/IR/IntrinsicsDirectX.td (+2)

diff --git a/clang/include/clang/Basic/Builtins.td b/clang/include/clang/Basic/Builtins.td
index 2c83dca248fb7d..a30953f4a94fa3 100644
--- a/clang/include/clang/Basic/Builtins.td
+++ b/clang/include/clang/Basic/Builtins.td
@@ -4548,6 +4548,12 @@ def HLSLLerp : LangBuiltin<"HLSL_LANG"> {
   let Prototype = "void(...)";
 }
 
+def HLSLRcp : LangBuiltin<"HLSL_LANG"> {
+  let Spellings = ["__builtin_hlsl_elementwise_rcp"];
+  let Attributes = [NoThrow, Const];
+  let Prototype = "void(...)";
+}
+
 // Builtins for XRay.
 def XRayCustomEvent : Builtin {
   let Spellings = ["__xray_customevent"];
diff --git a/clang/lib/CodeGen/CGBuiltin.cpp b/clang/lib/CodeGen/CGBuiltin.cpp
index e90014261217bc..aefc09767378a6 100644
--- a/clang/lib/CodeGen/CGBuiltin.cpp
+++ b/clang/lib/CodeGen/CGBuiltin.cpp
@@ -18057,6 +18057,14 @@ Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID,
         /*ReturnType*/ Op0->getType(), Intrinsic::dx_frac,
         ArrayRef<Value *>{Op0}, nullptr, "dx.frac");
   }
+  case Builtin::BI__builtin_hlsl_elementwise_rcp: {
+    Value *Op0 = EmitScalarExpr(E->getArg(0));
+    if (!E->getArg(0)->getType()->hasFloatingRepresentation())
+      llvm_unreachable("rcp operand must have a float representation");
+    return Builder.CreateIntrinsic(
+        /*ReturnType*/ Op0->getType(), Intrinsic::dx_rcp,
+        ArrayRef<Value *>{Op0}, nullptr, "dx.rcp");
+  }
   }
   return nullptr;
 }
diff --git a/clang/lib/Headers/hlsl/hlsl_intrinsics.h b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
index 5180530363889f..6174461cfa8802 100644
--- a/clang/lib/Headers/hlsl/hlsl_intrinsics.h
+++ b/clang/lib/Headers/hlsl/hlsl_intrinsics.h
@@ -831,6 +831,47 @@ uint64_t3 reversebits(uint64_t3);
 _HLSL_BUILTIN_ALIAS(__builtin_elementwise_bitreverse)
 uint64_t4 reversebits(uint64_t4);
 
+//===----------------------------------------------------------------------===//
+// rcp builtins
+//===----------------------------------------------------------------------===//
+
+/// \fn T rcp(T x)
+/// \brief Calculates a fast, approximate, per-component reciprocal ie 1 / \a x.
+/// \param x The specified input value.
+///
+/// The return value is the reciprocal of the \a x parameter.
+
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+half rcp(half);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+half2 rcp(half2);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+half3 rcp(half3);
+_HLSL_16BIT_AVAILABILITY(shadermodel, 6.2)
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+half4 rcp(half4);
+
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+float rcp(float);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+float2 rcp(float2);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+float3 rcp(float3);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+float4 rcp(float4);
+
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+double rcp(double);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+double2 rcp(double2);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+double3 rcp(double3);
+_HLSL_BUILTIN_ALIAS(__builtin_hlsl_elementwise_rcp)
+double4 rcp(double4);
+
 //===----------------------------------------------------------------------===//
 // round builtins
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 0d4d57db01c93a..237c838cb8c255 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -5280,6 +5280,7 @@ bool Sema::CheckHLSLBuiltinFunctionCall(unsigned BuiltinID, CallExpr *TheCall) {
       return true;
     break;
   }
+  case Builtin::BI__builtin_hlsl_elementwise_rcp:
   case Builtin::BI__builtin_hlsl_elementwise_frac: {
     if (PrepareBuiltinElementwiseMathOneArgCall(TheCall))
       return true;
diff --git a/clang/test/CodeGenHLSL/builtins/rcp.hlsl b/clang/test/CodeGenHLSL/builtins/rcp.hlsl
new file mode 100644
index 00000000000000..9b8406e1f0b605
--- /dev/null
+++ b/clang/test/CodeGenHLSL/builtins/rcp.hlsl
@@ -0,0 +1,53 @@
+// 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: define noundef half @
+// NATIVE_HALF: %dx.rcp = call half @llvm.dx.rcp.f16(
+// NATIVE_HALF: ret half %dx.rcp
+// NO_HALF: define noundef float @"?test_rcp_half@@YA$halff@$halff@@Z"(
+// NO_HALF: %dx.rcp = call float @llvm.dx.rcp.f32(
+// NO_HALF: ret float %dx.rcp
+half test_rcp_half(half p0) { return rcp(p0); }
+// NATIVE_HALF: define noundef <2 x half> @
+// NATIVE_HALF: %dx.rcp = call <2 x half> @llvm.dx.rcp.v2f16
+// NATIVE_HALF: ret <2 x half> %dx.rcp
+// NO_HALF: define noundef <2 x float> @
+// NO_HALF: %dx.rcp = call <2 x float> @llvm.dx.rcp.v2f32(
+// NO_HALF: ret <2 x float> %dx.rcp
+half2 test_rcp_half2(half2 p0) { return rcp(p0); }
+// NATIVE_HALF: define noundef <3 x half> @
+// NATIVE_HALF: %dx.rcp = call <3 x half> @llvm.dx.rcp.v3f16
+// NATIVE_HALF: ret <3 x half> %dx.rcp
+// NO_HALF: define noundef <3 x float> @
+// NO_HALF: %dx.rcp = call <3 x float> @llvm.dx.rcp.v3f32(
+// NO_HALF: ret <3 x float> %dx.rcp
+half3 test_rcp_half3(half3 p0) { return rcp(p0); }
+// NATIVE_HALF: define noundef <4 x half> @
+// NATIVE_HALF: %dx.rcp = call <4 x half> @llvm.dx.rcp.v4f16
+// NATIVE_HALF: ret <4 x half> %dx.rcp
+// NO_HALF: define noundef <4 x float> @
+// NO_HALF: %dx.rcp = call <4 x float> @llvm.dx.rcp.v4f32(
+// NO_HALF: ret <4 x float> %dx.rcp
+half4 test_rcp_half4(half4 p0) { return rcp(p0); }
+
+// CHECK: define noundef float @
+// CHECK: %dx.rcp = call float @llvm.dx.rcp.f32(
+// CHECK: ret float %dx.rcp
+float test_rcp_float(float p0) { return rcp(p0); }
+// CHECK: define noundef <2 x float> @
+// CHECK: %dx.rcp = call <2 x float> @llvm.dx.rcp.v2f32
+// CHECK: ret <2 x float> %dx.rcp
+float2 test_rcp_float2(float2 p0) { return rcp(p0); }
+// CHECK: define noundef <3 x float> @
+// CHECK: %dx.rcp = call <3 x float> @llvm.dx.rcp.v3f32
+// CHECK: ret <3 x float> %dx.rcp
+float3 test_rcp_float3(float3 p0) { return rcp(p0); }
+// CHECK: define noundef <4 x float> @
+// CHECK: %dx.rcp = call <4 x float> @llvm.dx.rcp.v4f32
+// CHECK: ret <4 x float> %dx.rcp
+float4 test_rcp_float4(float4 p0) { return rcp(p0); }
diff --git a/clang/test/SemaHLSL/BuiltIns/rcp-errors.hlsl b/clang/test/SemaHLSL/BuiltIns/rcp-errors.hlsl
new file mode 100644
index 00000000000000..dc4501dbd6d15a
--- /dev/null
+++ b/clang/test/SemaHLSL/BuiltIns/rcp-errors.hlsl
@@ -0,0 +1,27 @@
+
+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.6-library %s -fnative-half-type -emit-llvm -disable-llvm-passes -verify -verify-ignore-unexpected
+
+float test_too_few_arg() {
+  return __builtin_hlsl_elementwise_rcp();
+  // expected-error@-1 {{too few arguments to function call, expected 1, have 0}}
+}
+
+float2 test_too_many_arg(float2 p0) {
+  return __builtin_hlsl_elementwise_rcp(p0, p0);
+  // expected-error@-1 {{too many arguments to function call, expected 1, have 2}}
+}
+
+float builtin_bool_to_float_type_promotion(bool p1) {
+  return __builtin_hlsl_elementwise_rcp(p1);
+  // expected-error@-1 {{1st argument must be a vector, integer or floating point type (was 'bool')}}
+}
+
+float builtin_rcp_int_to_float_promotion(int p1) {
+  return __builtin_hlsl_elementwise_rcp(p1);
+  // expected-error@-1 {{passing 'int' to parameter of incompatible type 'float'}}
+}
+
+float2 builtin_rcp_int2_to_float2_promotion(int2 p1) {
+  return __builtin_hlsl_elementwise_rcp(p1);
+  // expected-error@-1 {{passing 'int2' (aka 'vector<int, 2>') to parameter of incompatible type '__attribute__((__vector_size__(2 * sizeof(float)))) float' (vector of 2 'float' values)}}
+}
diff --git a/llvm/include/llvm/IR/IntrinsicsDirectX.td b/llvm/include/llvm/IR/IntrinsicsDirectX.td
index b44d1c6d3d2f06..86defee4a563a7 100644
--- a/llvm/include/llvm/IR/IntrinsicsDirectX.td
+++ b/llvm/include/llvm/IR/IntrinsicsDirectX.td
@@ -31,4 +31,6 @@ def int_dx_lerp :
     Intrinsic<[LLVMScalarOrSameVectorWidth<0, LLVMVectorElementType<0>>],
     [llvm_anyvector_ty, LLVMScalarOrSameVectorWidth<0, LLVMVectorElementType<0>>,LLVMScalarOrSameVectorWidth<0, LLVMVectorElementType<0>>],
     [IntrNoMem, IntrWillReturn] >;
+
+def int_dx_rcp  : DefaultAttrsIntrinsic<[llvm_anyfloat_ty], [LLVMMatchType<0>]>;
 }

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