Various bits of framework needed for precise machine-level selection

DAG scheduling during isel. Most new functionality is currently
guarded by -enable-sched-cycles and -enable-sched-hazard.

Added InstrItineraryData::IssueWidth field, currently derived from
ARM itineraries, but could be initialized differently on other targets.

Added ScheduleHazardRecognizer::MaxLookAhead to indicate whether it is
active, and if so how many cycles of state it holds.

Added SchedulingPriorityQueue::HasReadyFilter to allowing gating entry
into the scheduler's available queue.

ScoreboardHazardRecognizer now accesses the ScheduleDAG in order to
get information about it's SUnits, provides RecedeCycle for bottom-up
scheduling, correctly computes scoreboard depth, tracks IssueCount, and
considers potential stall cycles when checking for hazards.

ScheduleDAGRRList now models machine cycles and hazards (under
flags). It tracks MinAvailableCycle, drives the hazard recognizer and
priority queue's ready filter, manages a new PendingQueue, properly
accounts for stall cycles, etc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122541 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 62 insertions, 14 deletions

diff --git a/lib/CodeGen/ScoreboardHazardRecognizer.cpp b/lib/CodeGen/ScoreboardHazardRecognizer.cpp
index d78b5d3ecbd..b00e0cd0998 100644
--- a/lib/CodeGen/ScoreboardHazardRecognizer.cpp
+++ b/lib/CodeGen/ScoreboardHazardRecognizer.cpp
@@ -13,7 +13,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define DEBUG_TYPE "sched-hazard"
+#define DEBUG_TYPE ::llvm::ScoreboardHazardRecognizer::DebugType
 #include "llvm/CodeGen/ScoreboardHazardRecognizer.h"
 #include "llvm/CodeGen/ScheduleDAG.h"
 #include "llvm/Support/Debug.h"
@@ -23,29 +23,48 @@
 
 using namespace llvm;
 
+#ifndef NDEBUG
+const char *ScoreboardHazardRecognizer::DebugType = "";
+#endif
+
 ScoreboardHazardRecognizer::
-ScoreboardHazardRecognizer(const InstrItineraryData *LItinData) :
-  ScheduleHazardRecognizer(), ItinData(LItinData) {
+ScoreboardHazardRecognizer(const InstrItineraryData *II,
+                           const ScheduleDAG *SchedDAG,
+                           const char *ParentDebugType) :
+  ScheduleHazardRecognizer(), ItinData(II), DAG(SchedDAG), IssueWidth(0),
+  IssueCount(0) {
+
+#ifndef NDEBUG
+  DebugType = ParentDebugType;
+#endif
+
   // Determine the maximum depth of any itinerary. This determines the
   // depth of the scoreboard. We always make the scoreboard at least 1
   // cycle deep to avoid dealing with the boundary condition.
   unsigned ScoreboardDepth = 1;
   if (ItinData && !ItinData->isEmpty()) {
+    IssueWidth = ItinData->IssueWidth;
+
     for (unsigned idx = 0; ; ++idx) {
       if (ItinData->isEndMarker(idx))
         break;
 
       const InstrStage *IS = ItinData->beginStage(idx);
       const InstrStage *E = ItinData->endStage(idx);
+      unsigned CurCycle = 0;
       unsigned ItinDepth = 0;
-      for (; IS != E; ++IS)
-        ItinDepth += IS->getCycles();
+      for (; IS != E; ++IS) {
+        unsigned StageDepth = CurCycle + IS->getCycles();
+        if (ItinDepth < StageDepth) ItinDepth = StageDepth;
+        CurCycle += IS->getNextCycles();
+      }
 
       // Find the next power-of-2 >= ItinDepth
       while (ItinDepth > ScoreboardDepth) {
         ScoreboardDepth *= 2;
       }
     }
+    MaxLookAhead = ScoreboardDepth;
   }
 
   ReservedScoreboard.reset(ScoreboardDepth);
@@ -56,6 +75,7 @@ ScoreboardHazardRecognizer(const InstrItineraryData *LItinData) :
 }
 
 void ScoreboardHazardRecognizer::Reset() {
+  IssueCount = 0;
   RequiredScoreboard.reset();
   ReservedScoreboard.reset();
 }
@@ -76,24 +96,46 @@ void ScoreboardHazardRecognizer::Scoreboard::dump() const {
   }
 }
 
+bool ScoreboardHazardRecognizer::atIssueLimit() const {
+  if (IssueWidth == 0)
+    return false;
+
+  return IssueCount == IssueWidth;
+}
+
 ScheduleHazardRecognizer::HazardType
-ScoreboardHazardRecognizer::getHazardType(SUnit *SU) {
+ScoreboardHazardRecognizer::getHazardType(SUnit *SU, int Stalls) {
   if (!ItinData || ItinData->isEmpty())
     return NoHazard;
 
-  unsigned cycle = 0;
+  // Note that stalls will be negative for bottom-up scheduling.
+  int cycle = Stalls;
 
   // Use the itinerary for the underlying instruction to check for
   // free FU's in the scoreboard at the appropriate future cycles.
-  unsigned idx = SU->getInstr()->getDesc().getSchedClass();
+
+  const TargetInstrDesc *TID = DAG->getInstrDesc(SU);
+  if (TID == NULL) {
+    // Don't check hazards for non-machineinstr Nodes.
+    return NoHazard;
+  }
+  unsigned idx = TID->getSchedClass();
   for (const InstrStage *IS = ItinData->beginStage(idx),
          *E = ItinData->endStage(idx); IS != E; ++IS) {
     // We must find one of the stage's units free for every cycle the
     // stage is occupied. FIXME it would be more accurate to find the
     // same unit free in all the cycles.
     for (unsigned int i = 0; i < IS->getCycles(); ++i) {
-      assert(((cycle + i) < RequiredScoreboard.getDepth()) &&
-             "Scoreboard depth exceeded!");
+      int StageCycle = cycle + (int)i;
+      if (StageCycle < 0)
+        continue;
+
+      if (StageCycle >= (int)RequiredScoreboard.getDepth()) {
+        assert((StageCycle - Stalls) < (int)RequiredScoreboard.getDepth() &&
+               "Scoreboard depth exceeded!");
+        // This stage was stalled beyond pipeline depth, so cannot conflict.
+        break;
+      }
 
       unsigned freeUnits = IS->getUnits();
       switch (IS->getReservationKind()) {
@@ -101,18 +143,18 @@ ScoreboardHazardRecognizer::getHazardType(SUnit *SU) {
        assert(0 && "Invalid FU reservation");
       case InstrStage::Required:
         // Required FUs conflict with both reserved and required ones
-        freeUnits &= ~ReservedScoreboard[cycle + i];
+        freeUnits &= ~ReservedScoreboard[StageCycle];
         // FALLTHROUGH
       case InstrStage::Reserved:
         // Reserved FUs can conflict only with required ones.
-        freeUnits &= ~RequiredScoreboard[cycle + i];
+        freeUnits &= ~RequiredScoreboard[StageCycle];
         break;
       }
 
       if (!freeUnits) {
         DEBUG(dbgs() << "*** Hazard in cycle " << (cycle + i) << ", ");
         DEBUG(dbgs() << "SU(" << SU->NodeNum << "): ");
-        DEBUG(SU->getInstr()->dump());
+        DEBUG(DAG->dumpNode(SU));
         return Hazard;
       }
     }
@@ -128,11 +170,15 @@ void ScoreboardHazardRecognizer::EmitInstruction(SUnit *SU) {
   if (!ItinData || ItinData->isEmpty())
     return;
 
+  ++IssueCount;
+
   unsigned cycle = 0;
 
   // Use the itinerary for the underlying instruction to reserve FU's
   // in the scoreboard at the appropriate future cycles.
-  unsigned idx = SU->getInstr()->getDesc().getSchedClass();
+  const TargetInstrDesc *TID = DAG->getInstrDesc(SU);
+  assert(TID && "The scheduler must filter non-machineinstrs");
+  unsigned idx = TID->getSchedClass();
   for (const InstrStage *IS = ItinData->beginStage(idx),
          *E = ItinData->endStage(idx); IS != E; ++IS) {
     // We must reserve one of the stage's units for every cycle the
@@ -179,11 +225,13 @@ void ScoreboardHazardRecognizer::EmitInstruction(SUnit *SU) {
 }
 
 void ScoreboardHazardRecognizer::AdvanceCycle() {
+  IssueCount = 0;
   ReservedScoreboard[0] = 0; ReservedScoreboard.advance();
   RequiredScoreboard[0] = 0; RequiredScoreboard.advance();
 }
 
 void ScoreboardHazardRecognizer::RecedeCycle() {
+  IssueCount = 0;
   ReservedScoreboard[ReservedScoreboard.getDepth()-1] = 0;
   ReservedScoreboard.recede();
   RequiredScoreboard[RequiredScoreboard.getDepth()-1] = 0;