Compute the critical path length through a trace.

Whenever both instruction depths and instruction heights are known in a
block, it is possible to compute the length of the critical path as
max(depth+height) over the instructions in the block.

The stored live-in lists make it possible to accurately compute the
length of a critical path that bypasses the current (small) block.

llvm-svn: 161197

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineTraceMetrics.h b/llvm/lib/CodeGen/MachineTraceMetrics.h
index b0edfeb7bd0..33c2d959885 100644
--- a/llvm/lib/CodeGen/MachineTraceMetrics.h
+++ b/llvm/lib/CodeGen/MachineTraceMetrics.h
@@ -174,6 +174,11 @@ public:
     /// Instruction heights have been computed. This implies hasValidHeight().
     bool HasValidInstrHeights;
 
+    /// Critical path length. This is the number of cycles in the longest data
+    /// dependency chain through the trace. This is only valid when both
+    /// HasValidInstrDepths and HasValidInstrHeights are set.
+    unsigned CriticalPath;
+
     /// Live-in registers. These registers are defined above the current block
     /// and used by this block or a block below it.
     /// This does not include PHI uses in the current block, but it does
@@ -224,6 +229,7 @@ public:
     void computeTrace(const MachineBasicBlock*);
     void computeDepthResources(const MachineBasicBlock*);
     void computeHeightResources(const MachineBasicBlock*);
+    unsigned computeCrossBlockCriticalPath(const TraceBlockInfo&);
     void computeInstrDepths(const MachineBasicBlock*);
     void computeInstrHeights(const MachineBasicBlock*);
     void addLiveIns(const MachineInstr *DefMI,