[PATCH] D85628: [HotColdSplitting] Add command line options for supplying cold function names via user input.

[Ruijie Fang via Phabricator via llvm-commits]

rjf created this revision.
rjf added reviewers: hiraditya, rcorcs.
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rjf requested review of this revision.

In some cases, the user might want to specify which functions are
explicitly cold. This commit adds two options, `cold-functions-list` and
`cold-functions-file` that enables the user to supply lists of cold
function names to hot/cold splitting. The optimization pass will then
mark any function encountered with the same name as cold.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D85628

Files:
  llvm/lib/Transforms/IPO/HotColdSplitting.cpp


Index: llvm/lib/Transforms/IPO/HotColdSplitting.cpp
===================================================================
--- llvm/lib/Transforms/IPO/HotColdSplitting.cpp
+++ llvm/lib/Transforms/IPO/HotColdSplitting.cpp
@@ -69,6 +69,11 @@
 #include "llvm/Transforms/Utils/ValueMapper.h"
 #include <algorithm>
 #include <cassert>
+#include <fstream>
+#include <iostream>
+#include <set>
+#include <sstream>
+#include <string>
 
 #define DEBUG_TYPE "hotcoldsplit"
 
@@ -85,6 +90,21 @@
                        cl::desc("Base penalty for splitting cold code (as a "
                                 "multiple of TCC_Basic)"));
 
+static cl::opt<std::string>
+    ColdFunctionsList("cold-functions-list", cl::init(""), cl::Hidden,
+                      cl::desc("Comma-separated list of functions to mark"
+                               " as cold during hot/cold splitting."));
+
+static cl::opt<std::string>
+    ColdFunctionsFile("cold-functions-file", cl::init(""), cl::Hidden,
+                      cl::desc("File name containing a newline-separated list"
+                               " of function names to mark as cold during"
+                               " hot/cold splitting."));
+
+// List of cold function names to watch out
+// during optimization.
+static std::set<std::string> UserSuppliedColdFunctions;
+
 namespace {
 // Same as blockEndsInUnreachable in CodeGen/BranchFolding.cpp. Do not modify
 // this function unless you modify the MBB version as well.
@@ -202,6 +222,12 @@
   if (PSI->isFunctionEntryCold(&F))
     return true;
 
+  // Alternatively, if user supplies any extra information
+  // on cold functions via command-line or file input,
+  // use them to determine if function is cold or not.
+  if (UserSuppliedColdFunctions.find(F.getName().str()) !=
+      UserSuppliedColdFunctions.end())
+    return true;
   return false;
 }
 
@@ -656,6 +682,32 @@
 bool HotColdSplitting::run(Module &M) {
   bool Changed = false;
   bool HasProfileSummary = (M.getProfileSummary(/* IsCS */ false) != nullptr);
+
+  // Read in user-defined cold function names, if any.
+  if (ColdFunctionsList != "") {
+    std::stringstream CFStream(ColdFunctionsList);
+    while (CFStream.good()) {
+      std::string CFName;
+      std::getline(CFStream, CFName, ',');
+      UserSuppliedColdFunctions.insert(CFName);
+    }
+  }
+
+  // Read in user-defined cold function names supplied
+  // by a file.
+  if (ColdFunctionsFile != "") {
+    if (ColdFunctionsFile == "stdin") {
+      std::string CFName;
+      while (std::cin >> CFName)
+        UserSuppliedColdFunctions.insert(CFName);
+    } else {
+      std::fstream FromFile(ColdFunctionsFile, std::fstream::in);
+      std::string CFName;
+      while (FromFile >> CFName)
+        UserSuppliedColdFunctions.insert(CFName);
+    }
+  }
+
   for (auto It = M.begin(), End = M.end(); It != End; ++It) {
     Function &F = *It;
 


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