[BOLT][AArch64] Refuse to run CDSplit pass (#159351)

LongJmp does not support warm blocks.
On builds without assertions, this may lead to unexpected crashes.

This patch exits with a clear message.

Author: paschalis-mpeis

bolt/include/bolt/Passes/SplitFunctions.h

@@ -18,25 +18,6 @@
 namespace llvm {
 namespace bolt {
 
-/// Strategy used to partition blocks into fragments.
-enum SplitFunctionsStrategy : char {
-  /// Split each function into a hot and cold fragment using profiling
-  /// information.
-  Profile2 = 0,
-  /// Split each function into a hot, warm, and cold fragment using
-  /// profiling information.
-  CDSplit,
-  /// Split each function into a hot and cold fragment at a randomly chosen
-  /// split point (ignoring any available profiling information).
-  Random2,
-  /// Split each function into N fragments at a randomly chosen split points
-  /// (ignoring any available profiling information).
-  RandomN,
-  /// Split all basic blocks of each function into fragments such that each
-  /// fragment contains exactly a single basic block.
-  All
-};
-
 class SplitStrategy {
 public:
   using BlockIt = BinaryFunction::BasicBlockOrderType::iterator;

bolt/include/bolt/Utils/CommandLineOpts.h

@@ -29,6 +29,25 @@ enum HeatmapModeKind {
   HM_Optional   // perf2bolt --heatmap
 };
 
+/// Strategy used to partition blocks into fragments.
+enum SplitFunctionsStrategy : char {
+  /// Split each function into a hot and cold fragment using profiling
+  /// information.
+  Profile2 = 0,
+  /// Split each function into a hot, warm, and cold fragment using
+  /// profiling information.
+  CDSplit,
+  /// Split each function into a hot and cold fragment at a randomly chosen
+  /// split point (ignoring any available profiling information).
+  Random2,
+  /// Split each function into N fragments at a randomly chosen split points
+  /// (ignoring any available profiling information).
+  RandomN,
+  /// Split all basic blocks of each function into fragments such that each
+  /// fragment contains exactly a single basic block.
+  All
+};
+
 using HeatmapBlockSizes = std::vector<unsigned>;
 struct HeatmapBlockSpecParser : public llvm::cl::parser<HeatmapBlockSizes> {
   explicit HeatmapBlockSpecParser(llvm::cl::Option &O)
@@ -78,6 +97,7 @@ extern llvm::cl::opt<std::string> OutputFilename;
 extern llvm::cl::opt<std::string> PerfData;
 extern llvm::cl::opt<bool> PrintCacheMetrics;
 extern llvm::cl::opt<bool> PrintSections;
+extern llvm::cl::opt<SplitFunctionsStrategy> SplitStrategy;
 
 // The format to use with -o in aggregation mode (perf2bolt)
 enum ProfileFormatKind { PF_Fdata, PF_YAML };

bolt/lib/Passes/LongJmp.cpp

@@ -895,6 +895,10 @@ void LongJmpPass::relaxLocalBranches(BinaryFunction &BF) {
 
 Error LongJmpPass::runOnFunctions(BinaryContext &BC) {
 
+  assert((opts::CompactCodeModel ||
+          opts::SplitStrategy != opts::SplitFunctionsStrategy::CDSplit) &&
+         "LongJmp cannot work with functions split in more than two fragments");
+
   if (opts::CompactCodeModel) {
     BC.outs()
         << "BOLT-INFO: relaxing branches for compact code model (<128MB)\n";

bolt/lib/Passes/SplitFunctions.cpp

@@ -86,29 +86,6 @@ static cl::opt<unsigned> SplitThreshold(
              "increase after splitting."),
     cl::init(0), cl::Hidden, cl::cat(BoltOptCategory));
 
-static cl::opt<SplitFunctionsStrategy> SplitStrategy(
-    "split-strategy", cl::init(SplitFunctionsStrategy::Profile2),
-    cl::values(clEnumValN(SplitFunctionsStrategy::Profile2, "profile2",
-                          "split each function into a hot and cold fragment "
-                          "using profiling information")),
-    cl::values(clEnumValN(SplitFunctionsStrategy::CDSplit, "cdsplit",
-                          "split each function into a hot, warm, and cold "
-                          "fragment using profiling information")),
-    cl::values(clEnumValN(
-        SplitFunctionsStrategy::Random2, "random2",
-        "split each function into a hot and cold fragment at a randomly chosen "
-        "split point (ignoring any available profiling information)")),
-    cl::values(clEnumValN(
-        SplitFunctionsStrategy::RandomN, "randomN",
-        "split each function into N fragments at a randomly chosen split "
-        "points (ignoring any available profiling information)")),
-    cl::values(clEnumValN(
-        SplitFunctionsStrategy::All, "all",
-        "split all basic blocks of each function into fragments such that each "
-        "fragment contains exactly a single basic block")),
-    cl::desc("strategy used to partition blocks into fragments"),
-    cl::cat(BoltOptCategory));
-
 static cl::opt<double> CallScale(
     "call-scale",
     cl::desc("Call score scale coefficient (when --split-strategy=cdsplit)"),
@@ -724,14 +701,14 @@ Error SplitFunctions::runOnFunctions(BinaryContext &BC) {
   // If split strategy is not CDSplit, then a second run of the pass is not
   // needed after function reordering.
   if (BC.HasFinalizedFunctionOrder &&
-      opts::SplitStrategy != SplitFunctionsStrategy::CDSplit)
+      opts::SplitStrategy != opts::SplitFunctionsStrategy::CDSplit)
     return Error::success();
 
   std::unique_ptr<SplitStrategy> Strategy;
   bool ForceSequential = false;
 
   switch (opts::SplitStrategy) {
-  case SplitFunctionsStrategy::CDSplit:
+  case opts::SplitFunctionsStrategy::CDSplit:
     // CDSplit runs two splitting passes: hot-cold splitting (SplitPrfoile2)
     // before function reordering and hot-warm-cold splitting
     // (SplitCacheDirected) after function reordering.
@@ -742,21 +719,21 @@ Error SplitFunctions::runOnFunctions(BinaryContext &BC) {
     opts::AggressiveSplitting = true;
     BC.HasWarmSection = true;
     break;
-  case SplitFunctionsStrategy::Profile2:
+  case opts::SplitFunctionsStrategy::Profile2:
     Strategy = std::make_unique<SplitProfile2>();
     break;
-  case SplitFunctionsStrategy::Random2:
+  case opts::SplitFunctionsStrategy::Random2:
     Strategy = std::make_unique<SplitRandom2>();
     // If we split functions randomly, we need to ensure that across runs with
     // the same input, we generate random numbers for each function in the same
     // order.
     ForceSequential = true;
     break;
-  case SplitFunctionsStrategy::RandomN:
+  case opts::SplitFunctionsStrategy::RandomN:
     Strategy = std::make_unique<SplitRandomN>();
     ForceSequential = true;
     break;
-  case SplitFunctionsStrategy::All:
+  case opts::SplitFunctionsStrategy::All:
     Strategy = std::make_unique<SplitAll>();
     break;
   }

bolt/lib/Rewrite/RewriteInstance.cpp

@@ -2115,6 +2115,13 @@ void RewriteInstance::adjustCommandLineOptions() {
     opts::SplitEH = false;
   }
 
+  if (BC->isAArch64() && !opts::CompactCodeModel &&
+      opts::SplitStrategy == opts::SplitFunctionsStrategy::CDSplit) {
+    BC->errs() << "BOLT-ERROR: CDSplit is not supported with LongJmp. Try with "
+                  "'--compact-code-model'\n";
+    exit(1);
+  }
+
   if (opts::StrictMode && !BC->HasRelocations) {
     BC->errs()
         << "BOLT-WARNING: disabling strict mode (-strict) in non-relocation "

bolt/lib/Utils/CommandLineOpts.cpp

@@ -104,6 +104,29 @@ ExecutionCountThreshold("execution-count-threshold",
   cl::Hidden,
   cl::cat(BoltOptCategory));
 
+cl::opt<SplitFunctionsStrategy> SplitStrategy(
+    "split-strategy", cl::init(SplitFunctionsStrategy::Profile2),
+    cl::values(clEnumValN(SplitFunctionsStrategy::Profile2, "profile2",
+                          "split each function into a hot and cold fragment "
+                          "using profiling information")),
+    cl::values(clEnumValN(SplitFunctionsStrategy::CDSplit, "cdsplit",
+                          "split each function into a hot, warm, and cold "
+                          "fragment using profiling information")),
+    cl::values(clEnumValN(
+        SplitFunctionsStrategy::Random2, "random2",
+        "split each function into a hot and cold fragment at a randomly chosen "
+        "split point (ignoring any available profiling information)")),
+    cl::values(clEnumValN(
+        SplitFunctionsStrategy::RandomN, "randomN",
+        "split each function into N fragments at a randomly chosen split "
+        "points (ignoring any available profiling information)")),
+    cl::values(clEnumValN(
+        SplitFunctionsStrategy::All, "all",
+        "split all basic blocks of each function into fragments such that each "
+        "fragment contains exactly a single basic block")),
+    cl::desc("strategy used to partition blocks into fragments"),
+    cl::cat(BoltOptCategory));
+
 bool HeatmapBlockSpecParser::parse(cl::Option &O, StringRef ArgName,
                                    StringRef Arg, HeatmapBlockSizes &Val) {
   // Parses a human-readable suffix into a shift amount or nullopt on error.

bolt/test/AArch64/unsupported-passes.test

@@ -3,6 +3,9 @@
 // REQUIRES: system-linux,asserts,target=aarch64{{.*}}
 
 RUN: %clang %cflags %p/../Inputs/hello.c -o %t -Wl,-q
-RUN: not llvm-bolt %t -o %t.bolt --frame-opt=all 2>&1 | FileCheck %s
+RUN: not llvm-bolt %t -o %t.bolt --frame-opt=all 2>&1 | FileCheck %s --check-prefix=CHECK-FRAME-OPT
 
-CHECK: BOLT-ERROR: frame-optimizer is supported only on X86
+CHECK-FRAME-OPT: BOLT-ERROR: frame-optimizer is supported only on X86
+
+RUN: not llvm-bolt %t -o %t.bolt split-functions --split-strategy=cdsplit 2>&1 | FileCheck %s --check-prefix=CHECK-CDSPLIT
+CHECK-CDSPLIT: BOLT-ERROR: CDSplit is not supported with LongJmp. Try with '--compact-code-model'