[Stackmap] Liveness Analysis Pass

This optional register liveness analysis pass can be enabled with either
-enable-stackmap-liveness, -enable-patchpoint-liveness, or both. The pass
traverses each basic block in a machine function. For each basic block the
instructions are processed in reversed order and if a patchpoint or stackmap
instruction is encountered the current live-out register set is encoded as a
register mask and attached to the instruction.

Later on during stackmap generation the live-out register mask is processed and
also emitted as part of the stackmap.

This information is optional and intended for optimization purposes only. This
will enable a client of the stackmap to reason about the registers it can use
and which registers need to be preserved.

Reviewed by Andy

llvm-svn: 197317

1 files changed, 128 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/StackMapLivenessAnalysis.cpp b/llvm/lib/CodeGen/StackMapLivenessAnalysis.cpp
new file mode 100644
index 00000000000..a374417a90e
--- /dev/null
+++ b/llvm/lib/CodeGen/StackMapLivenessAnalysis.cpp
@@ -0,0 +1,128 @@
+//===-- StackMapLivenessAnalysis.cpp - StackMap live Out Analysis ----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the StackMap Liveness analysis pass. The pass calculates
+// the liveness for each basic block in a function and attaches the register
+// live-out information to a stackmap or patchpoint intrinsic if present.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "stackmaps"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/CodeGen/MachineFrameInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionAnalysis.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/StackMapLivenessAnalysis.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+
+
+using namespace llvm;
+
+namespace llvm {
+cl::opt<bool> EnableStackMapLiveness("enable-stackmap-liveness",
+  cl::Hidden, cl::desc("Enable StackMap Liveness Analysis Pass"));
+cl::opt<bool> EnablePatchPointLiveness("enable-patchpoint-liveness",
+  cl::Hidden, cl::desc("Enable PatchPoint Liveness Analysis Pass"));
+}
+
+STATISTIC(NumStackMapFuncVisited, "Number of functions visited");
+STATISTIC(NumStackMapFuncSkipped, "Number of functions skipped");
+STATISTIC(NumBBsVisited,          "Number of basic blocks visited");
+STATISTIC(NumBBsHaveNoStackmap,   "Number of basic blocks with no stackmap");
+STATISTIC(NumStackMaps,           "Number of StackMaps visited");
+
+char StackMapLiveness::ID = 0;
+char &llvm::StackMapLivenessID = StackMapLiveness::ID;
+INITIALIZE_PASS(StackMapLiveness, "stackmap-liveness",
+                "StackMap Liveness Analysis", false, false)
+
+/// Default construct and initialize the pass.
+StackMapLiveness::StackMapLiveness() : MachineFunctionPass(ID) {
+  initializeStackMapLivenessPass(*PassRegistry::getPassRegistry());
+}
+
+/// Tell the pass manager which passes we depend on and what information we
+/// preserve.
+void StackMapLiveness::getAnalysisUsage(AnalysisUsage &AU) const {
+  // We preserve all information.
+  AU.setPreservesAll();
+  AU.setPreservesCFG();
+  // Default dependencie for all MachineFunction passes.
+  AU.addRequired<MachineFunctionAnalysis>();
+}
+
+/// Calculate the liveness information for the given machine function.
+bool StackMapLiveness::runOnMachineFunction(MachineFunction &_MF) {
+  DEBUG(dbgs() << "********** COMPUTING STACKMAP LIVENESS: "
+               << _MF.getName() << " **********\n");
+  MF = &_MF;
+  TRI = MF->getTarget().getRegisterInfo();
+  ++NumStackMapFuncVisited;
+
+  // Skip this function if there are no stackmaps or patchpoints to process.
+  if (!((MF->getFrameInfo()->hasStackMap() && EnableStackMapLiveness) ||
+        (MF->getFrameInfo()->hasPatchPoint() && EnablePatchPointLiveness))) {
+    ++NumStackMapFuncSkipped;
+    return false;
+  }
+  return calculateLiveness();
+}
+
+/// Performs the actual liveness calculation for the function.
+bool StackMapLiveness::calculateLiveness() {
+  bool HasChanged = false;
+  // For all basic blocks in the function.
+  for (MachineFunction::iterator MBBI = MF->begin(), MBBE = MF->end();
+       MBBI != MBBE; ++MBBI) {
+    DEBUG(dbgs() << "****** BB " << MBBI->getName() << " ******\n");
+    LiveRegs.init(TRI);
+    LiveRegs.addLiveOuts(MBBI);
+    bool HasStackMap = false;
+    // Reverse iterate over all instructions and add the current live register
+    // set to an instruction if we encounter a stackmap or patchpoint
+    // instruction.
+    for (MachineBasicBlock::reverse_iterator I = MBBI->rbegin(),
+         E = MBBI->rend(); I != E; ++I) {
+      int Opc = I->getOpcode();
+      if ((EnableStackMapLiveness && (Opc == TargetOpcode::STACKMAP)) ||
+          (EnablePatchPointLiveness && (Opc == TargetOpcode::PATCHPOINT))) {
+        addLiveOutSetToMI(*I);
+        HasChanged = true;
+        HasStackMap = true;
+        ++NumStackMaps;
+      }
+      DEBUG(dbgs() << "   " << *I << "   " << LiveRegs);
+      LiveRegs.stepBackward(*I);
+    }
+    ++NumBBsVisited;
+    if (!HasStackMap)
+      ++NumBBsHaveNoStackmap;
+  }
+  return HasChanged;
+}
+
+/// Add the current register live set to the instruction.
+void StackMapLiveness::addLiveOutSetToMI(MachineInstr &MI) {
+  uint32_t *Mask = createRegisterMask();
+  MachineOperand MO = MachineOperand::CreateRegLiveOut(Mask);
+  MI.addOperand(*MF, MO);
+}
+
+/// Create a register mask and initialize it with the registers from the
+/// register live set.
+uint32_t *StackMapLiveness::createRegisterMask() const {
+  // The mask is owned and cleaned up by the Machine Function.
+  uint32_t *Mask = MF->allocateRegisterMask(TRI->getNumRegs());
+  for (LivePhysRegs::const_iterator RI = LiveRegs.begin(), RE = LiveRegs.end();
+       RI != RE; ++RI)
+    Mask[*RI / 32] |= 1U << (*RI % 32);
+  return Mask;
+}