From 13372886a6d387c8847143744f26790a250f4360 Mon Sep 17 00:00:00 2001
From: Andrew Trick <atrick@apple.com>
Date: Thu, 25 Jul 2013 07:26:35 +0000
Subject: [PATCH] MI Sched: Register pressure heuristics.

Consider which set is being increased or decreased before comparing.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187110 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/CodeGen/RegisterPressure.h |  4 +++
 lib/CodeGen/MachineScheduler.cpp        | 40 ++++++++++++++++++++-----
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/include/llvm/CodeGen/RegisterPressure.h b/include/llvm/CodeGen/RegisterPressure.h
index 26701807467..bbc8ca5d28f 100644
--- a/include/llvm/CodeGen/RegisterPressure.h
+++ b/include/llvm/CodeGen/RegisterPressure.h
@@ -99,6 +99,10 @@ struct PressureElement {
   PressureElement(unsigned id, int inc): PSetID(id), UnitIncrease(inc) {}
 
   bool isValid() const { return PSetID != ~0U; }
+
+  // If signed PSetID is negative, it is invalid; convert it to INT_MAX to give
+  // it lowest priority.
+  int PSetRank() const { return PSetID & INT_MAX; }
 };
 
 /// Store the effects of a change in pressure on things that MI scheduler cares
diff --git a/lib/CodeGen/MachineScheduler.cpp b/lib/CodeGen/MachineScheduler.cpp
index 19e86d7e76f..4e3cc3c5d4f 100644
--- a/lib/CodeGen/MachineScheduler.cpp
+++ b/lib/CodeGen/MachineScheduler.cpp
@@ -2024,6 +2024,30 @@ static bool tryGreater(int TryVal, int CandVal,
   return false;
 }
 
+static bool tryPressure(const PressureElement &TryP,
+                        const PressureElement &CandP,
+                        ConvergingScheduler::SchedCandidate &TryCand,
+                        ConvergingScheduler::SchedCandidate &Cand,
+                        ConvergingScheduler::CandReason Reason) {
+  // If both candidates affect the same set, go with the smallest increase.
+  if (TryP.PSetID == CandP.PSetID) {
+    return tryLess(TryP.UnitIncrease, CandP.UnitIncrease, TryCand, Cand,
+                   Reason);
+  }
+  // If one candidate decreases and the other increases, go with it.
+  if (tryLess(TryP.UnitIncrease < 0, CandP.UnitIncrease < 0, TryCand, Cand,
+              Reason)) {
+    return true;
+  }
+  // If TryP has lower Rank, it has a higher priority.
+  int TryRank = TryP.PSetRank();
+  int CandRank = CandP.PSetRank();
+  // If the candidates are decreasing pressure, reverse priority.
+  if (TryP.UnitIncrease < 0)
+    std::swap(TryRank, CandRank);
+  return tryGreater(TryRank, CandRank, TryCand, Cand, Reason);
+}
+
 static unsigned getWeakLeft(const SUnit *SU, bool isTop) {
   return (isTop) ? SU->WeakPredsLeft : SU->WeakSuccsLeft;
 }
@@ -2089,15 +2113,15 @@ void ConvergingScheduler::tryCandidate(SchedCandidate &Cand,
                  TryCand, Cand, PhysRegCopy))
     return;
 
-  // Avoid exceeding the target's limit.
-  if (tryLess(TryCand.RPDelta.Excess.UnitIncrease,
-              Cand.RPDelta.Excess.UnitIncrease, TryCand, Cand, RegExcess))
+  // Avoid exceeding the target's limit. If signed PSetID is negative, it is
+  // invalid; convert it to INT_MAX to give it lowest priority.
+  if (tryPressure(TryCand.RPDelta.Excess, Cand.RPDelta.Excess, TryCand, Cand,
+                  RegExcess))
     return;
 
   // Avoid increasing the max critical pressure in the scheduled region.
-  if (tryLess(TryCand.RPDelta.CriticalMax.UnitIncrease,
-              Cand.RPDelta.CriticalMax.UnitIncrease,
-              TryCand, Cand, RegCritical))
+  if (tryPressure(TryCand.RPDelta.CriticalMax, Cand.RPDelta.CriticalMax,
+                  TryCand, Cand, RegCritical))
     return;
 
   // Keep clustered nodes together to encourage downstream peephole
@@ -2119,8 +2143,8 @@ void ConvergingScheduler::tryCandidate(SchedCandidate &Cand,
     return;
   }
   // Avoid increasing the max pressure of the entire region.
-  if (tryLess(TryCand.RPDelta.CurrentMax.UnitIncrease,
-              Cand.RPDelta.CurrentMax.UnitIncrease, TryCand, Cand, RegMax))
+  if (tryPressure(TryCand.RPDelta.CurrentMax, Cand.RPDelta.CurrentMax,
+                  TryCand, Cand, RegMax))
     return;
 
   // Avoid critical resource consumption and balance the schedule.
-- 
2.34.1