Start scaffolding for a MachineTraceMetrics analysis pass.

This is still a work in progress.

Out-of-order CPUs usually execute instructions from multiple basic
blocks simultaneously, so it is necessary to look at longer traces when
estimating the performance effects of code transformations.

The MachineTraceMetrics analysis will pick a typical trace through a
given basic block and provide performance metrics for the trace. Metrics
will include:

- Instruction count through the trace.
- Issue count per functional unit.
- Critical path length, and per-instruction 'slack'.

These metrics can be used to determine the performance limiting factor
when executing the trace, and how it will be affected by a code
transformation.

Initially, this will be used by the early if-conversion pass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160796 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 0 deletions

diff --git a/include/llvm/CodeGen/Passes.h b/include/llvm/CodeGen/Passes.h
index c80f6dcdb5..0cddff8d9d 100644
--- a/include/llvm/CodeGen/Passes.h
+++ b/include/llvm/CodeGen/Passes.h
@@ -392,6 +392,10 @@ namespace llvm {
   /// into tails of their predecessors.
   extern char &TailDuplicateID;
 
+  /// MachineTraceMetrics - This pass computes critical path and CPU resource
+  /// usage in an ensemble of traces.
+  extern char &MachineTraceMetricsID;
+
   /// EarlyIfConverter - This pass performs if-conversion on SSA form by
   /// inserting cmov instructions.
   extern char &EarlyIfConverterID;