[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

@@ -6011,10 +6011,27 @@ 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));
 

clang/lib/CodeGen/TargetBuiltins/AMDGPU.cpp

@@ -31,6 +31,27 @@ using namespace CodeGen;
 using namespace llvm;
 
 namespace {
+
+// Has second type mangled argument.
+static Value *
+emitBinaryExpMaybeConstrainedFPBuiltin(CodeGenFunction &CGF, const CallExpr *E,
+                                       Intrinsic::ID IntrinsicID,
+                                       Intrinsic::ID ConstrainedIntrinsicID) {
+  llvm::Value *Src0 = CGF.EmitScalarExpr(E->getArg(0));
+  llvm::Value *Src1 = CGF.EmitScalarExpr(E->getArg(1));
+
+  CodeGenFunction::CGFPOptionsRAII FPOptsRAII(CGF, E);
+  if (CGF.Builder.getIsFPConstrained()) {
+    Function *F = CGF.CGM.getIntrinsic(ConstrainedIntrinsicID,
+                                       {Src0->getType(), Src1->getType()});
+    return CGF.Builder.CreateConstrainedFPCall(F, {Src0, Src1});
+  }
+
+  Function *F =
+      CGF.CGM.getIntrinsic(IntrinsicID, {Src0->getType(), Src1->getType()});
+  return CGF.Builder.CreateCall(F, {Src0, Src1});
+}
+
 // If \p E is not null pointer, insert address space cast to match return
 // type of \p E if necessary.
 Value *EmitAMDGPUDispatchPtr(CodeGenFunction &CGF,
@@ -1876,6 +1897,30 @@ 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/test/CodeGen/logb_scalbn.c

@@ -0,0 +1,29 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 5
+// RUN: %clang -cc1 -triple amdgcn-amd-amdhsa -emit-llvm -o - %s | FileCheck %s
+
+// CHECK-LABEL: define dso_local void @my_kernel(
+// 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 double @llvm.fabs.f64(double 1.600000e+01)
+// CHECK-NEXT:    [[TMP4:%.*]] = fcmp one double [[TMP3]], 0x7FF0000000000000
+// CHECK-NEXT:    [[TMP5:%.*]] = select i1 [[TMP4]], double [[TMP2]], double [[TMP3]]
+// CHECK-NEXT:    [[TMP6:%.*]] = select i1 false, double 0xFFF0000000000000, double [[TMP5]]
+// CHECK-NEXT:    [[CONV:%.*]] = fptrunc double [[TMP6]] to float
+// CHECK-NEXT:    store float [[CONV]], ptr [[D1_ASCAST]], align 4
+// CHECK-NEXT:    [[TMP7:%.*]] = call double @llvm.ldexp.f64.i32(double 1.600000e+01, i32 10)
+// CHECK-NEXT:    [[CONV1:%.*]] = fptrunc double [[TMP7]] to float
+// CHECK-NEXT:    store float [[CONV1]], ptr [[D2_ASCAST]], align 4
+// CHECK-NEXT:    ret void
+//
+void my_kernel(){
+  float D1 = __builtin_logb((float)16);
+  float D2 = __builtin_scalbn((float)16, 10);
+}
+