[HEXAGON] Add basic block limit for RDF optimizations (#81071)

Skip RDF optimizations if a function contains a number of basic blocks
that is more than a limit

---------

Co-authored-by: Yashas Andaluri <quic_yandalur@quicinc.com>

llvm/lib/Target/Hexagon/HexagonOptAddrMode.cpp

@@ -47,6 +47,8 @@ static cl::opt<int> CodeGrowthLimit("hexagon-amode-growth-limit",
   cl::Hidden, cl::init(0), cl::desc("Code growth limit for address mode "
   "optimization"));
 
+extern cl::opt<unsigned> RDFFuncBlockLimit;
+
 namespace llvm {
 
   FunctionPass *createHexagonOptAddrMode();
@@ -856,6 +858,14 @@ bool HexagonOptAddrMode::runOnMachineFunction(MachineFunction &MF) {
   if (skipFunction(MF.getFunction()))
     return false;
 
+  // Perform RDF optimizations only if number of basic blocks in the
+  // function is less than the limit
+  if (MF.size() > RDFFuncBlockLimit) {
+    LLVM_DEBUG(dbgs() << "Skipping " << getPassName()
+                      << ": too many basic blocks\n");
+    return false;
+  }
+
   bool Changed = false;
   auto &HST = MF.getSubtarget<HexagonSubtarget>();
   MRI = &MF.getRegInfo();

llvm/lib/Target/Hexagon/HexagonRDFOpt.cpp

@@ -50,6 +50,9 @@ static unsigned RDFCount = 0;
 static cl::opt<unsigned>
     RDFLimit("hexagon-rdf-limit",
              cl::init(std::numeric_limits<unsigned>::max()));
+
+extern cl::opt<unsigned> RDFFuncBlockLimit;
+
 static cl::opt<bool> RDFDump("hexagon-rdf-dump", cl::Hidden);
 static cl::opt<bool> RDFTrackReserved("hexagon-rdf-track-reserved", cl::Hidden);
 
@@ -285,6 +288,14 @@ bool HexagonRDFOpt::runOnMachineFunction(MachineFunction &MF) {
   if (skipFunction(MF.getFunction()))
     return false;
 
+  // Perform RDF optimizations only if number of basic blocks in the
+  // function is less than the limit
+  if (MF.size() > RDFFuncBlockLimit) {
+    if (RDFDump)
+      dbgs() << "Skipping " << getPassName() << ": too many basic blocks\n";
+    return false;
+  }
+
   if (RDFLimit.getPosition()) {
     if (RDFCount >= RDFLimit)
       return false;

llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp

@@ -39,6 +39,10 @@ static cl::opt<bool>
 static cl::opt<bool> EnableRDFOpt("rdf-opt", cl::Hidden, cl::init(true),
                                   cl::desc("Enable RDF-based optimizations"));
 
+cl::opt<unsigned> RDFFuncBlockLimit(
+    "rdf-bb-limit", cl::Hidden, cl::init(1000),
+    cl::desc("Basic block limit for a function for RDF optimizations"));
+
 static cl::opt<bool> DisableHardwareLoops("disable-hexagon-hwloops",
   cl::Hidden, cl::desc("Disable Hardware Loops for Hexagon target"));