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

[Abinaya Saravanan via llvm-commits]

https://github.com/quic-asaravan created https://github.com/llvm/llvm-project/pull/81071

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

>From 4a85ecd1b7c738fe4f77549bc567e1058d178d78 Mon Sep 17 00:00:00 2001
From: Yashas Andaluri <quic_yandalur at quicinc.com>
Date: Wed, 7 Feb 2024 09:50:13 -0800
Subject: [PATCH] Add basic block limit for RDF optimizations

Skip RDF optimizations if a function contains a number
of basic blocks that is more than a limit
---
 llvm/lib/Target/Hexagon/HexagonOptAddrMode.cpp   | 10 ++++++++++
 llvm/lib/Target/Hexagon/HexagonRDFOpt.cpp        | 11 +++++++++++
 llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp |  4 ++++
 3 files changed, 25 insertions(+)

diff --git a/llvm/lib/Target/Hexagon/HexagonOptAddrMode.cpp b/llvm/lib/Target/Hexagon/HexagonOptAddrMode.cpp
index aa31762a969609..0e82bf6e5331da 100644
--- a/llvm/lib/Target/Hexagon/HexagonOptAddrMode.cpp
+++ b/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();
diff --git a/llvm/lib/Target/Hexagon/HexagonRDFOpt.cpp b/llvm/lib/Target/Hexagon/HexagonRDFOpt.cpp
index 7eccbd2cb02362..4131f2a31755fb 100644
--- a/llvm/lib/Target/Hexagon/HexagonRDFOpt.cpp
+++ b/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;
diff --git a/llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp b/llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp
index e7a692d67ba015..7d4b420071c4a3 100644
--- a/llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp
+++ b/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"));