[SPIRV][HLSL] Add lowering of rsqrt to SPIRV

clang/lib/CodeGen/CGBuiltin.cpp

@@ -18331,7 +18331,7 @@ Value *CodeGenFunction::EmitHLSLBuiltinExpr(unsigned BuiltinID,
     if (!E->getArg(0)->getType()->hasFloatingRepresentation())
       llvm_unreachable("rsqrt operand must have a float representation");
     return Builder.CreateIntrinsic(
-        /*ReturnType=*/Op0->getType(), Intrinsic::dx_rsqrt,
+        /*ReturnType=*/Op0->getType(), CGM.getHLSLRuntime().getRsqrtIntrinsic(),
         ArrayRef<Value *>{Op0}, nullptr, "dx.rsqrt");
   }
   case Builtin::BI__builtin_hlsl_wave_get_lane_index: {

clang/lib/CodeGen/CGHLSLRuntime.h

@@ -75,6 +75,7 @@ class CGHLSLRuntime {
   GENERATE_HLSL_INTRINSIC_FUNCTION(All, all)
   GENERATE_HLSL_INTRINSIC_FUNCTION(Any, any)
   GENERATE_HLSL_INTRINSIC_FUNCTION(Lerp, lerp)
+  GENERATE_HLSL_INTRINSIC_FUNCTION(Rsqrt, rsqrt)
   GENERATE_HLSL_INTRINSIC_FUNCTION(ThreadId, thread_id)
 
   //===----------------------------------------------------------------------===//

llvm/include/llvm/IR/IntrinsicsSPIRV.td

@@ -62,4 +62,5 @@ let TargetPrefix = "spv" in {
   def int_spv_any : DefaultAttrsIntrinsic<[llvm_i1_ty], [llvm_any_ty]>;
   def int_spv_lerp : Intrinsic<[LLVMMatchType<0>], [llvm_anyfloat_ty, LLVMMatchType<0>,LLVMMatchType<0>], 
     [IntrNoMem, IntrWillReturn] >;
+  def int_spv_rsqrt : DefaultAttrsIntrinsic<[LLVMMatchType<0>], [llvm_anyfloat_ty]>;
 }

llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp

@@ -173,6 +173,9 @@ class SPIRVInstructionSelector : public InstructionSelector {
   bool selectFmix(Register ResVReg, const SPIRVType *ResType,
                   MachineInstr &I) const;
 
+  bool selectRsqrt(Register ResVReg, const SPIRVType *ResType,
+                   MachineInstr &I) const;
+
   void renderImm32(MachineInstrBuilder &MIB, const MachineInstr &I,
                    int OpIdx) const;
   void renderFImm32(MachineInstrBuilder &MIB, const MachineInstr &I,
@@ -1315,6 +1318,23 @@ bool SPIRVInstructionSelector::selectFmix(Register ResVReg,
       .constrainAllUses(TII, TRI, RBI);
 }
 
+bool SPIRVInstructionSelector::selectRsqrt(Register ResVReg,
+                                           const SPIRVType *ResType,
+                                           MachineInstr &I) const {
+
+  assert(I.getNumOperands() == 3);
+  assert(I.getOperand(2).isReg());
+  MachineBasicBlock &BB = *I.getParent();
+
+  return BuildMI(BB, I, I.getDebugLoc(), TII.get(SPIRV::OpExtInst))
+      .addDef(ResVReg)
+      .addUse(GR.getSPIRVTypeID(ResType))
+      .addImm(static_cast<uint32_t>(SPIRV::InstructionSet::GLSL_std_450))
+      .addImm(GL::InverseSqrt)
+      .addUse(I.getOperand(2).getReg())
+      .constrainAllUses(TII, TRI, RBI);
+}
+
 bool SPIRVInstructionSelector::selectBitreverse(Register ResVReg,
                                                 const SPIRVType *ResType,
                                                 MachineInstr &I) const {
@@ -1992,6 +2012,8 @@ bool SPIRVInstructionSelector::selectIntrinsic(Register ResVReg,
     return selectAny(ResVReg, ResType, I);
   case Intrinsic::spv_lerp:
     return selectFmix(ResVReg, ResType, I);
+  case Intrinsic::spv_rsqrt:
+    return selectRsqrt(ResVReg, ResType, I);
   case Intrinsic::spv_lifetime_start:
   case Intrinsic::spv_lifetime_end: {
     unsigned Op = IID == Intrinsic::spv_lifetime_start ? SPIRV::OpLifetimeStart

llvm/test/CodeGen/SPIRV/hlsl-intrinsics/rsqrt.ll

@@ -0,0 +1,29 @@
+; RUN: llc -O0 -mtriple=spirv-unknown-unknown %s -o - | FileCheck %s
+; RUN: %if spirv-tools %{ llc -O0 -mtriple=spirv-unknown-unknown %s -o - -filetype=obj | spirv-val %}
+
+; CHECK: OpExtInstImport "GLSL.std.450"
+
+define noundef float @rsqrt_float(float noundef %a) {
+entry:
+; CHECK: %[[#]] = OpExtInst %[[#]] %[[#]] InverseSqrt %[[#]]
+  %elt.rsqrt = call float @llvm.spv.rsqrt.f32(float %a)
+  ret float %elt.rsqrt
+}
+
+define noundef half @rsqrt_half(half noundef %a) {
+entry:
+; CHECK: %[[#]] = OpExtInst %[[#]] %[[#]] InverseSqrt %[[#]]
+  %elt.rsqrt = call half @llvm.spv.rsqrt.f16(half %a)
+  ret half %elt.rsqrt
+}
+
+define noundef double @rsqrt_double(double noundef %a) {
+entry:
+; CHECK: %[[#]] = OpExtInst %[[#]] %[[#]] InverseSqrt %[[#]]
+  %elt.rsqrt = call double @llvm.spv.rsqrt.f64(double %a)
+  ret double %elt.rsqrt
+}
+
+declare half @llvm.spv.sqrt.f16(half)
+declare float @llvm.spv.sqrt.f32(float)
+declare float @llvm.spv.sqrt.f64(float)