Flag-gate the new pass and resolve review feedback

Author: mingmingl-llvm

llvm/lib/CodeGen/StaticDataSplitter.cpp

@@ -83,7 +83,10 @@ bool StaticDataSplitter::splitJumpTablesWithProfiles(
     MachineFunction &MF, MachineJumpTableInfo &MJTI) {
   int NumChangedJumpTables = 0;
   // Regard a jump table as hot by default. If the source and all of destination
-  // blocks are cold, regard the jump table as cold.
+  // blocks are cold, regard the jump table as cold. While a destination block
+  // does not read a jump table (unless it's also a source block), a hot
+  // destination heuristically makes its jump table hot to accommodate for
+  // potential profile data skews (from sampled profiles, for example).
   DataHotness Hotness = DataHotness::Hot;
   for (const auto &MBB : MF) {
     // IMPORTANT, `getJumpTableIndex` is a thin wrapper around per-target
@@ -121,11 +124,9 @@ bool StaticDataSplitter::splitJumpTables(MachineFunction &MF) {
   if (!MJTI || MJTI->getJumpTables().empty())
     return false;
 
-  // Place jump tables according to block hotness if block counters are
-  // available. Check function entry count because BFI depends on it to derive
-  // block counters.
+  // Place jump tables according to block hotness if function has profile data.
   if (PSI && PSI->hasProfileSummary() && MBFI &&
-      MF.getFunction().getEntryCount())
+      MF.getFunction().hasProfileData())
     return splitJumpTablesWithProfiles(MF, *MJTI);
 
   // Conservatively place all jump tables in the hot-suffixed section if profile

llvm/lib/CodeGen/TargetPassConfig.cpp

@@ -263,6 +263,11 @@ static cl::opt<bool>
     GCEmptyBlocks("gc-empty-basic-blocks", cl::init(false), cl::Hidden,
                   cl::desc("Enable garbage-collecting empty basic blocks"));
 
+static cl::opt<bool>
+    SplitStaticData("split-static-data", cl::Hidden, cl::init(false),
+                    cl::desc("Split static data sections into hot and cold "
+                             "section ones using profile information"));
+
 /// Allow standard passes to be disabled by command line options. This supports
 /// simple binary flags that either suppress the pass or do nothing.
 /// i.e. -disable-mypass=false has no effect.
@@ -1256,8 +1261,9 @@ void TargetPassConfig::addMachinePasses() {
                "performance.\n";
       }
     }
-    addPass(createStaticDataSplitterPass());
     addPass(createMachineFunctionSplitterPass());
+    if (SplitStaticData)
+      addPass(createStaticDataSplitterPass());
   }
   // We run the BasicBlockSections pass if either we need BB sections or BB
   // address map (or both).