[BranchProbability] move options for 'likely' and 'unlikely'

[spatel]

Summary

This makes the settings available for use in other passes by housing them within the Support lib, but NFC otherwise.

See D98898 for the proposed usage in SimplifyCFG (where this was originally included).

[spatel]

Patch updated:
Added a clang update that I missed before. That appears to be the only other user in clang+llvm.

[lebedev.ri]

SGTM, thanks.

llvm/include/llvm/Support/BranchProbability.h

 //===- BranchProbability.h - Branch Probability Wrapper ---------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // Definition of BranchProbability shared by IR and Machine Instructions.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_BRANCHPROBABILITY_H
 #define LLVM_SUPPORT_BRANCHPROBABILITY_H
 
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/DataTypes.h"
 #include <algorithm>
 #include <cassert>
 #include <climits>
 #include <numeric>
 
 namespace llvm {
 
+extern cl::opt<uint32_t> LikelyBranchWeight;
+extern cl::opt<uint32_t> UnlikelyBranchWeight;
+
 class raw_ostream;
 
 // This class represents Branch Probability as a non-negative fraction that is
 // no greater than 1. It uses a fixed-point-like implementation, in which the
 // denominator is always a constant value (here we use 1<<31 for maximum
 // precision).
 class BranchProbability {
   // Numerator

llvm/include/llvm/Transforms/Scalar/LowerExpectIntrinsic.h

 ///
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_TRANSFORMS_SCALAR_LOWEREXPECTINTRINSIC_H
 #define LLVM_TRANSFORMS_SCALAR_LOWEREXPECTINTRINSIC_H
 
 #include "llvm/IR/Function.h"
 #include "llvm/IR/PassManager.h"
-#include "llvm/Support/CommandLine.h"
 
 namespace llvm {
 
 struct LowerExpectIntrinsicPass : PassInfoMixin<LowerExpectIntrinsicPass> {
   /// Run the pass over the function.
   ///
   /// This will lower all of the expect intrinsic calls in this function into
   /// branch weight metadata. That metadata will subsequently feed the analysis
   /// of the probabilities and frequencies of the CFG. After running this pass,
   /// no more expect intrinsics remain, allowing the rest of the optimizer to
   /// ignore them.
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
 };
 
-extern cl::opt<uint32_t> LikelyBranchWeight;
-extern cl::opt<uint32_t> UnlikelyBranchWeight;
 }
 
 #endif

llvm/lib/Support/BranchProbability.cpp

 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 
 using namespace llvm;
 
+// These default values are chosen to represent an extremely skewed outcome for
+// a condition, but they leave some room for interpretation by later passes.
+//
+// If the documentation for __builtin_expect() was made explicit that it should
+// only be used in extreme cases, we could make this ratio higher. As it stands,
+// programmers may be using __builtin_expect() / llvm.expect to annotate that a
+// branch is only mildly likely or unlikely to be taken.
+cl::opt<uint32_t> llvm::LikelyBranchWeight(
+    "likely-branch-weight", cl::Hidden, cl::init(2000),
+    cl::desc("Weight of the branch likely to be taken (default = 2000)"));
+cl::opt<uint32_t> llvm::UnlikelyBranchWeight(
+    "unlikely-branch-weight", cl::Hidden, cl::init(1),
+    cl::desc("Weight of the branch unlikely to be taken (default = 1)"));
+
 constexpr uint32_t BranchProbability::D;
 
 raw_ostream &BranchProbability::print(raw_ostream &OS) const {
   if (isUnknown())
     return OS << "?%";
 
   // Get a percentage rounded to two decimal digits. This avoids
   // implementation-defined rounding inside printf.

llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp

 #include "llvm/IR/Function.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
+#include "llvm/Support/BranchProbability.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Transforms/Scalar.h"
 
 using namespace llvm;
 
 #define DEBUG_TYPE "lower-expect-intrinsic"
 
 STATISTIC(ExpectIntrinsicsHandled,
           "Number of 'expect' intrinsic instructions handled");
 
-// These default values are chosen to represent an extremely skewed outcome for
-// a condition, but they leave some room for interpretation by later passes.
-//
-// If the documentation for __builtin_expect() was made explicit that it should
-// only be used in extreme cases, we could make this ratio higher. As it stands,
-// programmers may be using __builtin_expect() / llvm.expect to annotate that a
-// branch is likely or unlikely to be taken.
-//
-// There is a known dependency on this ratio in CodeGenPrepare when transforming
-// 'select' instructions. It may be worthwhile to hoist these values to some
-// shared space, so they can be used directly by other passes.
-
-cl::opt<uint32_t> llvm::LikelyBranchWeight(
-    "likely-branch-weight", cl::Hidden, cl::init(2000),
-    cl::desc("Weight of the branch likely to be taken (default = 2000)"));
-cl::opt<uint32_t> llvm::UnlikelyBranchWeight(
-    "unlikely-branch-weight", cl::Hidden, cl::init(1),
-    cl::desc("Weight of the branch unlikely to be taken (default = 1)"));
-
 static std::tuple<uint32_t, uint32_t>
 getBranchWeight(Intrinsic::ID IntrinsicID, CallInst *CI, int BranchCount) {
   if (IntrinsicID == Intrinsic::expect) {
     // __builtin_expect
     return std::make_tuple(LikelyBranchWeight.getValue(),
                            UnlikelyBranchWeight.getValue());
   } else {
     // __builtin_expect_with_probability