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

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 change was originally included).

Differential Revision: https://reviews.llvm.org/D98945

Author: rotateright

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -42,8 +42,8 @@
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Operator.h"
+#include "llvm/Support/BranchProbability.h"
 #include "llvm/Support/CRC.h"
-#include "llvm/Transforms/Scalar/LowerExpectIntrinsic.h"
 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
 using namespace clang;
 using namespace CodeGen;

llvm/include/llvm/Support/BranchProbability.h

@@ -13,6 +13,7 @@
 #ifndef LLVM_SUPPORT_BRANCHPROBABILITY_H
 #define LLVM_SUPPORT_BRANCHPROBABILITY_H
 
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/DataTypes.h"
 #include <algorithm>
 #include <cassert>
@@ -21,6 +22,9 @@
 
 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

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

@@ -17,7 +17,6 @@
 
 #include "llvm/IR/Function.h"
 #include "llvm/IR/PassManager.h"
-#include "llvm/Support/CommandLine.h"
 
 namespace llvm {
 
@@ -32,8 +31,6 @@ struct LowerExpectIntrinsicPass : PassInfoMixin<LowerExpectIntrinsicPass> {
   PreservedAnalyses run(Function &F, FunctionAnalysisManager &);
 };
 
-extern cl::opt<uint32_t> LikelyBranchWeight;
-extern cl::opt<uint32_t> UnlikelyBranchWeight;
 }
 
 #endif

llvm/lib/Support/BranchProbability.cpp

@@ -19,6 +19,20 @@
 
 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 {

llvm/lib/Transforms/Scalar/LowerExpectIntrinsic.cpp

@@ -24,6 +24,7 @@
 #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"
 
@@ -34,25 +35,6 @@ using namespace llvm;
 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) {