Unsafe.Unlikely (Assume) draft implementation

src/coreclr/src/jit/importer.cpp

@@ -4127,6 +4127,19 @@ GenTree* Compiler::impIntrinsic(GenTree* newobjThis,
  break;
  }
 
+ case NI_System_Runtime_CompilerServices_Unsafe_Unlikely:
+ {
+ if (compCurBB->bbJumpKind == BBJ_COND)
+ {
+ // I guess actually we need to change weight for a specific edge
+ // rather than for the whole block (it can be non-cold for other conditions)
+ // however, bbPreds are not calcaluted at this moment...
+ compCurBB->bbNext->bbFlags |= BBF_RUN_RARELY;
+ compCurBB->bbNext->setBBWeight(BB_ZERO_WEIGHT);
+ }
+ break;
+ }
+
 #ifdef FEATURE_HW_INTRINSICS
  case NI_System_Math_FusedMultiplyAdd:
  case NI_System_MathF_FusedMultiplyAdd:
@@ -4430,6 +4443,14 @@ NamedIntrinsic Compiler::lookupNamedIntrinsic(CORINFO_METHOD_HANDLE method)
  }
  }
  }
+ else if ((strcmp(namespaceName, "Internal.Runtime.CompilerServices") == 0) ||
+ (strcmp(namespaceName, "System.Runtime.CompilerServices") == 0))
+ {
+ if ((strcmp(className, "Unsafe") == 0) && (strcmp(methodName, "Unlikely") == 0))
+ {
+ result = NI_System_Runtime_CompilerServices_Unsafe_Unlikely;
+ }
+ }
 #if defined(TARGET_XARCH) // We currently only support BSWAP on x86
  else if (strcmp(namespaceName, "System.Buffers.Binary") == 0)
  {

src/coreclr/src/jit/namedintrinsiclist.h

@@ -21,6 +21,7 @@ enum NamedIntrinsic : unsigned short
  NI_System_GC_KeepAlive,
  NI_System_Type_get_IsValueType,
  NI_System_Type_IsAssignableFrom,
+ NI_System_Runtime_CompilerServices_Unsafe_Unlikely,
 
 #ifdef FEATURE_HW_INTRINSICS
  NI_IsSupported_True,

src/libraries/System.Private.CoreLib/src/Internal/Runtime/CompilerServices/Unsafe.cs

@@ -443,5 +443,13 @@ public static void SkipInit<T>(out T value)
 
  // ret
  }
+
+ [Intrinsic]
+ [NonVersionable]
+ [MethodImpl(MethodImplOptions.AggressiveInlining)]
+ public static bool Unlikely(bool condition)
+ {
+ return condition;
+ }
  }
 }

src/libraries/System.Runtime.CompilerServices.Unsafe/src/System.Runtime.CompilerServices.Unsafe.il

@@ -162,6 +162,14 @@
  ret
  } // end of method Unsafe::SkipInit
 
+ //.method public hidebysig static bool Unlikely (bool condition) cil managed aggressiveinlining
+ //{
+ // .custom instance void System.Runtime.Versioning.NonVersionableAttribute::.ctor() = ( 01 00 00 00 )
+ // .maxstack 1
+ // ldarg.0
+ // ret
+ //} // end of method Unsafe::Unlikely
+
  .method public hidebysig static int32 SizeOf<T>() cil managed aggressiveinlining
  {
  .custom instance void System.Runtime.Versioning.NonVersionableAttribute::.ctor() = ( 01 00 00 00 )

src/mono/mono/mini/intrinsics.c

@@ -588,6 +588,17 @@ emit_unsafe_intrinsics (MonoCompile *cfg, MonoMethod *cmethod, MonoMethodSignatu
  MONO_ADD_INS (cfg->cbb, ins);
  return ins;
  }
+ else if (!strcmp (cmethod->name, "Unlikely") && COMPILE_LLVM (cfg)) {
+ g_assert (fsig->param_count == 1);
+
+ // LLVM should expand it as @llvm.expect.i32
+ MONO_INST_NEW (cfg, ins, OP_UNLIKELY32);
+ ins->type = STACK_I4;
+ ins->dreg = mono_alloc_ireg (cfg);
+ ins->sreg1 = args [0]->dreg;
+ MONO_ADD_INS (cfg->cbb, ins);
+ return ins;
+ }
 #endif
 
  return NULL;

src/mono/mono/mini/mini-llvm.c

@@ -321,6 +321,7 @@ typedef enum {
  INTRINS_TRUNCF,
  INTRINS_COPYSIGN,
  INTRINS_COPYSIGNF,
+ INTRINS_EXPECT_I32,
  INTRINS_EXPECT_I8,
  INTRINS_EXPECT_I1,
  INTRINS_CTPOP_I32,
@@ -8057,6 +8058,12 @@ process_bb (EmitContext *ctx, MonoBasicBlock *bb)
 #endif /* ENABLE_NETCORE */
 #endif /* SIMD */
 
+ case OP_UNLIKELY32: {
+ LLVMValueRef args [] = { lhs, LLVMConstInt (LLVMInt32Type (), 0, FALSE) };
+ values [ins->dreg] = LLVMBuildCall (builder, get_intrins (ctx, INTRINS_EXPECT_I32), args, 2, "");
+ break;
+ }
+
  case OP_DUMMY_USE:
  break;
 
@@ -9365,6 +9372,7 @@ static IntrinsicDesc intrinsics[] = {
  {INTRINS_TRUNCF, "llvm.trunc.f32"},
  {INTRINS_COPYSIGN, "llvm.copysign.f64"},
  {INTRINS_COPYSIGNF, "llvm.copysign.f32"},
+ {INTRINS_EXPECT_I32, "llvm.expect.i32"},
  {INTRINS_EXPECT_I8, "llvm.expect.i8"},
  {INTRINS_EXPECT_I1, "llvm.expect.i1"},
  {INTRINS_CTPOP_I32, "llvm.ctpop.i32"},
@@ -9590,6 +9598,9 @@ add_intrinsic (LLVMModuleRef module, int id)
  case INTRINS_POW:
  AddFunc2 (module, name, LLVMDoubleType (), LLVMDoubleType (), LLVMDoubleType ());
  break;
+ case INTRINS_EXPECT_I32:
+ AddFunc2 (module, name, LLVMInt32Type (), LLVMInt32Type (), LLVMInt32Type ());
+ break;
  case INTRINS_EXPECT_I8:
  AddFunc2 (module, name, LLVMInt8Type (), LLVMInt8Type (), LLVMInt8Type ());
  break;

src/mono/mono/mini/mini-ops.h

@@ -1456,4 +1456,4 @@ MINI_OP(OP_LZCNT64, "lzcnt64", LREG, LREG, NONE)
 MINI_OP(OP_POPCNT32, "popcnt32", IREG, IREG, NONE)
 MINI_OP(OP_POPCNT64, "popcnt64", LREG, LREG, NONE)
 
-
+MINI_OP(OP_UNLIKELY32, "unlikely", IREG, IREG, NONE)