[BOLT] Prevent unsetting unknown control flow for split jump table

In case of a function with unknown control flow but with a single jump
table and a single jump table site, we attempt to match the jump table
and a site and update block successors using jump table targets.
Restrict this behavior for split jump tables which have targets in a
fragment function.

Fixes https://github.com/llvm/llvm-project/issues/60795.

Reviewed By: #bolt, rafauler

Differential Revision: https://reviews.llvm.org/D144602

1 files changed, 6 insertions, 1 deletions

diff --git a/bolt/lib/Core/BinaryFunction.cpp b/bolt/lib/Core/BinaryFunction.cpp
index d1a046791d46..13c5fd444ea4 100644
--- a/bolt/lib/Core/BinaryFunction.cpp
+++ b/bolt/lib/Core/BinaryFunction.cpp
@@ -1770,6 +1770,8 @@ bool BinaryFunction::validateExternallyReferencedOffsets() {
 bool BinaryFunction::postProcessIndirectBranches(
     MCPlusBuilder::AllocatorIdTy AllocId) {
   auto addUnknownControlFlow = [&](BinaryBasicBlock &BB) {
+    LLVM_DEBUG(dbgs() << "BOLT-DEBUG: adding unknown control flow in " << *this
+                      << " for " << BB.getName() << "\n");
     HasUnknownControlFlow = true;
     BB.removeAllSuccessors();
     for (uint64_t PossibleDestination : ExternallyReferencedOffsets)
@@ -1877,7 +1879,10 @@ bool BinaryFunction::postProcessIndirectBranches(
   // references, then we should be able to derive the jump table even if we
   // fail to match the pattern.
   if (HasUnknownControlFlow && NumIndirectJumps == 1 &&
-      JumpTables.size() == 1 && LastIndirectJump) {
+      JumpTables.size() == 1 && LastIndirectJump &&
+      !BC.getJumpTableContainingAddress(LastJT)->IsSplit) {
+    LLVM_DEBUG(dbgs() << "BOLT-DEBUG: unsetting unknown control flow in "
+                      << *this << '\n');
     BC.MIB->setJumpTable(*LastIndirectJump, LastJT, LastJTIndexReg, AllocId);
     HasUnknownControlFlow = false;