[CodeGen] Implement [[likely]] and [[unlikely]] for while and for loop.

The attribute has no effect on a do statement since the path of execution
will always include its substatement.

It adds a diagnostic when the attribute is used on an infinite while loop
since the codegen omits the branch here. Since the likelihood attributes
have no effect on a do statement no diagnostic will be issued for
do [[unlikely]] {...} while(0);

Differential Revision: https://reviews.llvm.org/D89899

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 2616226..4cf857a 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -1407,6 +1407,13 @@ private:
   llvm::MDNode *createProfileWeightsForLoop(const Stmt *Cond,
                                             uint64_t LoopCount) const;
 
+  /// Calculate the branch weight for PGO data or the likelihood attribute.
+  /// The function tries to get the weight of \ref createProfileWeightsForLoop.
+  /// If that fails it gets the weight of \ref createBranchWeights.
+  llvm::MDNode *createProfileOrBranchWeightsForLoop(const Stmt *Cond,
+                                                    uint64_t LoopCount,
+                                                    const Stmt *Body) const;
+
 public:
   /// Increment the profiler's counter for the given statement by \p StepV.
   /// If \p StepV is null, the default increment is 1.