[llvm] AMDGPU: Add NextUseAnalysis Pass (PR #178873)

[Konstantina Mitropoulou via llvm-commits]

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@@ -0,0 +1,2349 @@
+//===---------------------- AMDGPUNextUseAnalysis.cpp ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "AMDGPUNextUseAnalysis.h"
+#include "AMDGPU.h"
+#include "GCNRegPressure.h"
+#include "GCNSubtarget.h"
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/IR/ModuleSlotTracker.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/JSON.h"
+#include "llvm/Support/Timer.h"
+#include "llvm/Support/ToolOutputFile.h"
+#include "llvm/Support/raw_ostream.h"
+
+#include <algorithm>
+#include <cmath>
+#include <limits>
+#include <queue>
+#include <string>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "amdgpu-next-use-analysis"
+
+//==============================================================================
+// Options etc
+//==============================================================================
+namespace {
+
+cl::opt<bool> DumpNextUseDistance("amdgpu-next-use-analysis-dump-distance",
+                                  cl::init(false), cl::Hidden);
+
+cl::opt<std::string>
+    DumpNextUseDistanceAsJson("amdgpu-next-use-analysis-dump-distance-as-json",
+                              cl::Hidden);
+cl::opt<bool>
+    DumpNextUseDistanceVerbose("amdgpu-next-use-analysis-dump-distance-verbose",
+                               cl::init(false), cl::Hidden);
+
+cl::opt<AMDGPUNextUseAnalysis::CompatibilityMode> CompatModeOpt(
+    "amdgpu-next-use-analysis-compatibility-mode", cl::Hidden,
+    cl::init(AMDGPUNextUseAnalysis::CompatibilityMode::Graphics),
+    cl::values(clEnumValN(AMDGPUNextUseAnalysis::CompatibilityMode::Graphics,
+                          "graphics", "TBD"),
+               clEnumValN(AMDGPUNextUseAnalysis::CompatibilityMode::Compute,
+                          "compute", "TBD")));
+} // namespace
+
+//==============================================================================
+// LiveRegUse - Represents a live register use with its distance. Used for
+// tracking and sorting register uses by distance.
+//==============================================================================
+namespace {
+using UseDistancePair = AMDGPUNextUseAnalysis::UseDistancePair;
+struct LiveRegUse : public UseDistancePair {
+  // 'nullptr' indicates an unset/invalid state.
+  LiveRegUse() : UseDistancePair(nullptr, 0) {}
+  LiveRegUse(const MachineOperand *Use, NextUseDistance Dist)
+      : UseDistancePair(Use, Dist) {}
+  LiveRegUse(const UseDistancePair &P) : UseDistancePair(P) {}
+
+  bool isUnset() const { return Use == nullptr; }
+
+  Register getReg() const { return Use->getReg(); }
+  unsigned getSubReg() const { return Use->getSubReg(); }
+  LaneBitmask getLaneMask(const SIRegisterInfo *TRI) const {
+    return TRI->getSubRegIndexLaneMask(Use->getSubReg());
+  }
+
+  bool isCloserThan(const LiveRegUse &X) const {
+    if (Dist < X.Dist)
+      return true;
+
+    if (Dist > X.Dist)
+      return false;
+
+    if (Use == X.Use)
+      return false;
+
+    // Ugh. In computeMode PHIs and the first non-PHI instruction have id
+    // 0. In this case, consider PHIs as less than the first non-PHI
+    // instruction.
+    const MachineInstr *ThisMI = Use->getParent();
+    const MachineInstr *XMI = X.Use->getParent();
+    const MachineBasicBlock *ThisMBB = ThisMI->getParent();
+    if (ThisMBB == XMI->getParent()) {
+      bool XIsPhiOp = ThisMI->isPHI();
+      bool YIsPhiOp = XMI->isPHI();
+      if (XIsPhiOp && !YIsPhiOp && XMI == &(*ThisMBB->getFirstNonPHI()))
+        return true;
+    }
+
+    // Ensure deterministic results
+    return X.getReg() < getReg();
+  }
+};
+
+inline bool updateClosest(LiveRegUse &Closest, const LiveRegUse &X) {
+  if (!Closest.Use || X.isCloserThan(Closest)) {
+    Closest = X;
+    return true;
+  }
+  return false;
+}
----------------
kmitropoulou wrote:

Can you please add a dump() function here and in other classes to help with debugging?

https://github.com/llvm/llvm-project/pull/178873