[llvm] [AMDGPU] GCNRegPressure printing pass for testing. (PR #70031)

[Matt Arsenault via llvm-commits]

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@@ -487,3 +488,111 @@ LLVM_DUMP_METHOD
 void GCNRegPressure::dump() const { dbgs() << print(*this); }
 
 #endif
+
+static cl::opt<bool> UseDownwardTracker(
+    "amdgpu-print-rp-downward",
+    cl::desc("Use GCNDownwardRPTracker for GCNRegPressurePrinter pass"),
+    cl::init(false), cl::Hidden);
+
+char llvm::GCNRegPressurePrinter::ID = 0;
+char &llvm::GCNRegPressurePrinterID = GCNRegPressurePrinter::ID;
+
+INITIALIZE_PASS(GCNRegPressurePrinter, "amdgpu-print-rp", "", true, true)
+
+bool GCNRegPressurePrinter::runOnMachineFunction(MachineFunction &MF) {
+  if (skipFunction(MF.getFunction()))
+    return false;
+
+  const MachineRegisterInfo &MRI = MF.getRegInfo();
+  const LiveIntervals &LIS = getAnalysis<LiveIntervals>();
+  
+  auto &OS = dbgs();
+
+// Leading spaces are important for YAML syntax.
+#define PFX "  "
+
+  OS << "---\nname: " << MF.getName() << "\nbody:             |\n";
+
+  auto printRP = [](const GCNRegPressure &RP) {
+    return Printable([&RP](raw_ostream &OS) {
+      OS << format(PFX "  %-5d", RP.getSGPRNum())
+         << format(" %-5d", RP.getVGPRNum(false));
+    });
+  };
+
+  // Register pressure before and at an instruction (in program order).
+  SmallVector<std::pair<GCNRegPressure, GCNRegPressure>, 16> RP;
+
+  for (auto &MBB : MF) {
+    RP.clear();
+    RP.reserve(MBB.size());
+
+    OS << PFX;
+    MBB.printName(OS);
+    OS << ":\n";
+
+    if (MBB.empty()) {
+      SlotIndex MBBSI = LIS.getSlotIndexes()->getMBBStartIdx(&MBB);
+      GCNRPTracker::LiveRegSet LRThrough = getLiveRegs(MBBSI, LIS, MRI);
+      GCNRegPressure RP = getRegPressure(MRI, LRThrough);
+      OS << PFX "  Live-through:" << llvm::print(LRThrough, MRI);
+      OS << PFX "  SGPR  VGPR\n" << printRP(RP) << '\n';
+      continue;
+    }
+
+    GCNRPTracker::LiveRegSet LRAtMBBBegin, LRAtMBBEnd;
+    GCNRegPressure RPAtMBBEnd;
+    
+    if (UseDownwardTracker) {
+      GCNDownwardRPTracker RPT(LIS);
+      RPT.reset(MBB.instr_front());
----------------
arsenm wrote:

why instr_front instead of just front?

https://github.com/llvm/llvm-project/pull/70031