[BOLT] Add structure of CDSplit to SplitFunctions (#73430)

This commit establishes the general structure of the CDSplit strategy in
SplitFunctions without incorporating the exact splitting logic. With
-split-functions -split-strategy=cdsplit, the SplitFunctions pass will
run twice: the first time is before function reordering and functions
are hot-cold split; the second time is after function reordering and
functions are hot-warm-cold split based on the fixed function ordering.
Currently, all functions are hot-warm split after the entry block in the
second splitting pass. Subsequent commits will introduce the precise
splitting logic. NFC.

1 files changed, 7 insertions, 0 deletions

diff --git a/bolt/lib/Rewrite/BinaryPassManager.cpp b/bolt/lib/Rewrite/BinaryPassManager.cpp
index 37de3ea..9946608 100644
--- a/bolt/lib/Rewrite/BinaryPassManager.cpp
+++ b/bolt/lib/Rewrite/BinaryPassManager.cpp
@@ -430,6 +430,13 @@ void BinaryFunctionPassManager::runAllPasses(BinaryContext &BC) {
   Manager.registerPass(
       std::make_unique<ReorderFunctions>(PrintReorderedFunctions));
 
+  // This is the second run of the SplitFunctions pass required by certain
+  // splitting strategies (e.g. cdsplit). Running the SplitFunctions pass again
+  // after ReorderFunctions allows the finalized function order to be utilized
+  // to make more sophisticated splitting decisions, like hot-warm-cold
+  // splitting.
+  Manager.registerPass(std::make_unique<SplitFunctions>(PrintSplit));
+
   // Print final dyno stats right while CFG and instruction analysis are intact.
   Manager.registerPass(
       std::make_unique<DynoStatsPrintPass>(