[AMDGPU][clang] provide device implementation for __builtin_logb and __builtin_scalbn

Clang generates library calls for __builtin_* functions which can be a problem for GPUs that cannot handle them.
This patch generates a device implementations for __builtin_logb and __builtin_scalbn.

Author: choikwa

clang/lib/CodeGen/CGBuiltin.cpp

@@ -6621,10 +6621,27 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
   }
   }
 
+  // These will be emitted as Intrinsic later.
+  auto NeedsDeviceOverload = [&](unsigned BuiltinID) {
+    if (getTarget().getTriple().isAMDGCN()) {
+      switch (BuiltinID) {
+      default:
+        return false;
+      case Builtin::BIlogb:
+      case Builtin::BI__builtin_logb:
+      case Builtin::BIscalbn:
+      case Builtin::BI__builtin_scalbn:
+        return true;
+      }
+    }
+    return false;
+  };
+
   // If this is an alias for a lib function (e.g. __builtin_sin), emit
   // the call using the normal call path, but using the unmangled
   // version of the function name.
-  if (getContext().BuiltinInfo.isLibFunction(BuiltinID))
+  if (!NeedsDeviceOverload(BuiltinID) &&
+      getContext().BuiltinInfo.isLibFunction(BuiltinID))
     return emitLibraryCall(*this, FD, E,
                            CGM.getBuiltinLibFunction(FD, BuiltinID));
 
@@ -20910,6 +20927,30 @@ Value *CodeGenFunction::EmitAMDGPUBuiltinExpr(unsigned BuiltinID,
   case AMDGPU::BI__builtin_amdgcn_s_prefetch_data:
     return emitBuiltinWithOneOverloadedType<2>(
         *this, E, Intrinsic::amdgcn_s_prefetch_data);
+  case Builtin::BIlogb:
+  case Builtin::BI__builtin_logb: {
+    auto Src0 = EmitScalarExpr(E->getArg(0));
+    auto FrExpFunc = CGM.getIntrinsic(Intrinsic::amdgcn_frexp_exp,
+                                      {Builder.getInt32Ty(), Src0->getType()});
+    auto FrExp = Builder.CreateCall(FrExpFunc, Src0);
+    auto Add = Builder.CreateAdd(
+        FrExp, ConstantInt::getSigned(FrExp->getType(), -1), "", false, true);
+    auto SIToFP = Builder.CreateSIToFP(Add, Builder.getDoubleTy());
+    auto Fabs = emitBuiltinWithOneOverloadedType<1>(*this, E, Intrinsic::fabs);
+    auto FCmpONE = Builder.CreateFCmpONE(
+        Fabs, ConstantFP::getInfinity(Builder.getDoubleTy()));
+    auto Sel1 = Builder.CreateSelect(FCmpONE, SIToFP, Fabs);
+    auto FCmpOEQ =
+        Builder.CreateFCmpOEQ(Src0, ConstantFP::getZero(Builder.getDoubleTy()));
+    auto Sel2 = Builder.CreateSelect(
+        FCmpOEQ, ConstantFP::getInfinity(Builder.getDoubleTy(), /*Neg*/ true),
+        Sel1);
+    return Sel2;
+  }
+  case Builtin::BIscalbn:
+  case Builtin::BI__builtin_scalbn:
+    return emitBinaryExpMaybeConstrainedFPBuiltin(
+        *this, E, Intrinsic::ldexp, Intrinsic::experimental_constrained_ldexp);
   default:
     return nullptr;
   }

clang/lib/CodeGen/CodeGenModule.h

@@ -1231,6 +1231,11 @@ class CodeGenModule : public CodeGenTypeCache {
       llvm::FunctionType *FnType = nullptr, bool DontDefer = false,
       ForDefinition_t IsForDefinition = NotForDefinition);
 
+  /// Given a builtin id for a function, return a Function* for device
+  /// overload implementation.
+  llvm::Constant *getDeviceLibFunction(const FunctionDecl *FD,
+                                       unsigned BuiltinID);
+
   /// Given a builtin id for a function like "__builtin_fabsf", return a
   /// Function* for "fabsf".
   llvm::Constant *getBuiltinLibFunction(const FunctionDecl *FD,

clang/test/CodeGenHIP/logb_scalbn.hip

@@ -0,0 +1,32 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 5
+// RUN: %clang --cuda-device-only -nogpuinc -nogpulib -emit-llvm -S -o - %s | FileCheck %s
+#include <math.h>
+#define __device__ __attribute__((device))
+
+// CHECK-LABEL: define hidden void @_Z9my_kernelv(
+// CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[D1:%.*]] = alloca float, align 4, addrspace(5)
+// CHECK-NEXT:    [[D2:%.*]] = alloca float, align 4, addrspace(5)
+// CHECK-NEXT:    [[D1_ASCAST:%.*]] = addrspacecast ptr addrspace(5) [[D1]] to ptr
+// CHECK-NEXT:    [[D2_ASCAST:%.*]] = addrspacecast ptr addrspace(5) [[D2]] to ptr
+// CHECK-NEXT:    [[TMP0:%.*]] = call i32 @llvm.amdgcn.frexp.exp.i32.f64(double 1.600000e+01)
+// CHECK-NEXT:    [[TMP1:%.*]] = add nsw i32 [[TMP0]], -1
+// CHECK-NEXT:    [[TMP2:%.*]] = sitofp i32 [[TMP1]] to double
+// CHECK-NEXT:    [[TMP3:%.*]] = call contract double @llvm.fabs.f64(double 1.600000e+01)
+// CHECK-NEXT:    [[TMP4:%.*]] = fcmp contract one double [[TMP3]], 0x7FF0000000000000
+// CHECK-NEXT:    [[TMP5:%.*]] = select contract i1 [[TMP4]], double [[TMP2]], double [[TMP3]]
+// CHECK-NEXT:    [[TMP6:%.*]] = select contract i1 false, double 0xFFF0000000000000, double [[TMP5]]
+// CHECK-NEXT:    [[CONV:%.*]] = fptrunc contract double [[TMP6]] to float
+// CHECK-NEXT:    store float [[CONV]], ptr [[D1_ASCAST]], align 4
+// CHECK-NEXT:    [[TMP7:%.*]] = call contract double @llvm.ldexp.f64.i32(double 1.600000e+01, i32 10)
+// CHECK-NEXT:    [[CONV1:%.*]] = fptrunc contract double [[TMP7]] to float
+// CHECK-NEXT:    store float [[CONV1]], ptr [[D2_ASCAST]], align 4
+// CHECK-NEXT:    ret void
+//
+__device__ void my_kernel(){
+
+  float D1 = __builtin_logb((float)16);
+  float D2 = __builtin_scalbn((float)16, 10);
+}
+