Add trace accessor methods, implement primitive if-conversion heuristic.

Compare the critical paths of the two traces through an if-conversion
candidate. If the difference is larger than the branch brediction
penalty, reject the if-conversion. If would never pay.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161433 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 36 insertions, 11 deletions

diff --git a/lib/CodeGen/MachineTraceMetrics.h b/lib/CodeGen/MachineTraceMetrics.h
index 33c2d95988..626b28b322 100644
--- a/lib/CodeGen/MachineTraceMetrics.h
+++ b/lib/CodeGen/MachineTraceMetrics.h
@@ -188,6 +188,19 @@ public:
     void print(raw_ostream&) const;
   };
 
+  /// InstrCycles represents the cycle height and depth of an instruction in a
+  /// trace.
+  struct InstrCycles {
+    /// Earliest issue cycle as determined by data dependencies and instruction
+    /// latencies from the beginning of the trace. Data dependencies from
+    /// before the trace are not included.
+    unsigned Depth;
+
+    /// Minimum number of cycles from this instruction is issued to the of the
+    /// trace, as determined by data dependencies and instruction latencies.
+    unsigned Height;
+  };
+
   /// A trace represents a plausible sequence of executed basic blocks that
   /// passes through the current basic block one. The Trace class serves as a
   /// handle to internal cached data structures.
@@ -195,6 +208,8 @@ public:
     Ensemble &TE;
     TraceBlockInfo &TBI;
 
+    unsigned getBlockNum() const { return &TBI - &TE.BlockInfo[0]; }
+
   public:
     explicit Trace(Ensemble &te, TraceBlockInfo &tbi) : TE(te), TBI(tbi) {}
     void print(raw_ostream&) const;
@@ -203,19 +218,29 @@ public:
     unsigned getInstrCount() const {
       return TBI.InstrDepth + TBI.InstrHeight;
     }
-  };
 
-  /// InstrCycles represents the cycle height and depth of an instruction in a
-  /// trace.
-  struct InstrCycles {
-    /// Earliest issue cycle as determined by data dependencies and instruction
-    /// latencies from the beginning of the trace. Data dependencies from
-    /// before the trace are not included.
-    unsigned Depth;
+    /// Return the resource dpeth of the top/bottom of the trace center block.
+    /// This is the number of cycles required to execute all instructions from
+    /// the trace head to the trace center block. The resource depth only
+    /// considers execution resources, it ignores data dependencies.
+    /// When Bottom is set, instructions in the trace center block are included.
+    unsigned getResourceDepth(bool Bottom) const;
+
+    /// Return the length of the (data dependency) critical path through the
+    /// trace.
+    unsigned getCriticalPath() const { return TBI.CriticalPath; }
+
+    /// Return the depth and height of MI. The depth is only valid for
+    /// instructions in or above the trace center block. The height is only
+    /// valid for instructions in or below the trace center block.
+    InstrCycles getInstrCycles(const MachineInstr *MI) const {
+      return TE.Cycles.lookup(MI);
+    }
 
-    /// Minimum number of cycles from this instruction is issued to the of the
-    /// trace, as determined by data dependencies and instruction latencies.
-    unsigned Height;
+    /// Return the slack of MI. This is the number of cycles MI can be delayed
+    /// before the critical path becomes longer.
+    /// MI must be an instruction in the trace center block.
+    unsigned getInstrSlack(const MachineInstr *MI) const;
   };
 
   /// A trace ensemble is a collection of traces selected using the same