MIsched: add an ILP window property to machine model.

This was an experimental option, but needs to be defined
per-target. e.g. PPC A2 needs to aggressively hide latency.

I converted some in-order scheduling tests to A2. Hal is working on
more test cases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@171946 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 19 insertions, 4 deletions

diff --git a/include/llvm/CodeGen/TargetSchedule.h b/include/llvm/CodeGen/TargetSchedule.h
index 4c4a2a8b95..484d7e200a 100644
--- a/include/llvm/CodeGen/TargetSchedule.h
+++ b/include/llvm/CodeGen/TargetSchedule.h
@@ -84,6 +84,9 @@ public:
   /// \brief Maximum number of micro-ops that may be scheduled per cycle.
   unsigned getIssueWidth() const { return SchedModel.IssueWidth; }
 
+  /// \brief Number of cycles the OOO processor is expected to hide.
+  unsigned getILPWindow() const { return SchedModel.ILPWindow; }
+
   /// \brief Return the number of issue slots required for this MI.
   unsigned getNumMicroOps(const MachineInstr *MI,
                           const MCSchedClassDesc *SC = 0) const;
diff --git a/include/llvm/MC/MCSchedule.h b/include/llvm/MC/MCSchedule.h
index 0c71ee5135..9e9474952a 100644
--- a/include/llvm/MC/MCSchedule.h
+++ b/include/llvm/MC/MCSchedule.h
@@ -155,7 +155,7 @@ public:
   //      Optional InstrItinerary OperandCycles provides expected latency.
   //      TODO: can't yet specify both min and expected latency per operand.
   int MinLatency;
-  static const unsigned DefaultMinLatency = -1;
+  static const int DefaultMinLatency = -1;
 
   // LoadLatency is the expected latency of load instructions.
   //
@@ -172,6 +172,16 @@ public:
   unsigned HighLatency;
   static const unsigned DefaultHighLatency = 10;
 
+  // ILPWindow is the number of cycles that the scheduler effectively ignores
+  // before attempting to hide latency. This should be zero for in-order cpus to
+  // always hide expected latency. For out-of-order cpus, it may be tweaked as
+  // desired to roughly approximate instruction buffers. The actual threshold is
+  // not very important for an OOO processor, as long as it isn't too high. A
+  // nonzero value helps avoid rescheduling to hide latency when its is fairly
+  // obviously useless and makes register pressure heuristics more effective.
+  unsigned ILPWindow;
+  static const unsigned DefaultILPWindow = 0;
+
   // MispredictPenalty is the typical number of extra cycles the processor
   // takes to recover from a branch misprediction.
   unsigned MispredictPenalty;
@@ -196,6 +206,7 @@ public:
                   MinLatency(DefaultMinLatency),
                   LoadLatency(DefaultLoadLatency),
                   HighLatency(DefaultHighLatency),
+                  ILPWindow(DefaultILPWindow),
                   MispredictPenalty(DefaultMispredictPenalty),
                   ProcID(0), ProcResourceTable(0), SchedClassTable(0),
                   NumProcResourceKinds(0), NumSchedClasses(0),
@@ -205,12 +216,12 @@ public:
   }
 
   // Table-gen driven ctor.
-  MCSchedModel(unsigned iw, int ml, unsigned ll, unsigned hl, unsigned mp,
-               unsigned pi, const MCProcResourceDesc *pr,
+  MCSchedModel(unsigned iw, int ml, unsigned ll, unsigned hl, unsigned ilp,
+               unsigned mp, unsigned pi, const MCProcResourceDesc *pr,
                const MCSchedClassDesc *sc, unsigned npr, unsigned nsc,
                const InstrItinerary *ii):
     IssueWidth(iw), MinLatency(ml), LoadLatency(ll), HighLatency(hl),
-    MispredictPenalty(mp), ProcID(pi), ProcResourceTable(pr),
+    ILPWindow(ilp), MispredictPenalty(mp), ProcID(pi), ProcResourceTable(pr),
     SchedClassTable(sc), NumProcResourceKinds(npr), NumSchedClasses(nsc),
     InstrItineraries(ii) {}
 
diff --git a/include/llvm/Target/TargetSchedule.td b/include/llvm/Target/TargetSchedule.td
index 0da82fdd89..b7920bae8a 100644
--- a/include/llvm/Target/TargetSchedule.td
+++ b/include/llvm/Target/TargetSchedule.td
@@ -76,6 +76,7 @@ class SchedMachineModel {
   int IssueWidth = -1; // Max micro-ops that may be scheduled per cycle.
   int MinLatency = -1; // Determines which instrucions are allowed in a group.
                        // (-1) inorder (0) ooo, (1): inorder +var latencies.
+  int ILPWindow = -1;  // Cycles of latency likely hidden by hardware buffers.
   int LoadLatency = -1; // Cycles for loads to access the cache.
   int HighLatency = -1; // Approximation of cycles for "high latency" ops.
   int MispredictPenalty = -1; // Extra cycles for a mispredicted branch.