[CodeGen] Add Performance Monitor

Add support for -polly-codegen-perf-monitoring. When performance monitoring is enabled, we emit performance monitoring code during code generation that prints after program exit statistics about the total number of cycles executed as well as the number of cycles spent in scops. This gives an estimate on how useful polyhedral optimizations might be for a given program. Example output: Polly runtime information ------------------------- Total: 783110081637 Scops: 663718949365 In the future, we might also add functionality to measure how much time is spent in optimized scops and how many cycles are spent in the fallback code. Reviewers: bollu,sebpop Tags: #polly Differential Revision: https://reviews.llvm.org/D31599 llvm-svn: 299359
llvm · Apr 3, 2017 · 65371af · 65371af
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diff --git a/polly/include/polly/CodeGen/PerfMonitor.h b/polly/include/polly/CodeGen/PerfMonitor.h
@@ -0,0 +1,132 @@
+//===--- PerfMonitor.h --- Monitor time spent in scops --------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef PERF_MONITOR_H
+#define PERF_MONITOR_H
+
+#include "polly/CodeGen/IRBuilder.h"
+
+namespace llvm {
+class Function;
+class Module;
+class Value;
+class Instruction;
+} // namespace llvm
+
+namespace polly {
+
+class PerfMonitor {
+public:
+  /// Create a new performance monitor.
+  ///
+  /// @param M The module for which to generate the performance monitor.
+  PerfMonitor(llvm::Module *M);
+
+  /// Initialize the performance monitor.
+  ///
+  /// Ensure that all global variables, functions, and callbacks needed to
+  /// manage the performance monitor are initialized and registered.
+  void initialize();
+
+  /// Mark the beginning of a timing region.
+  ///
+  /// @param InsertBefore The instruction before which the timing region starts.
+  void insertRegionStart(llvm::Instruction *InserBefore);
+
+  /// Mark the end of a timing region.
+  ///
+  /// @param InsertBefore The instruction before which the timing region starts.
+  void insertRegionEnd(llvm::Instruction *InsertBefore);
+
+private:
+  llvm::Module *M;
+  PollyIRBuilder Builder;
+
+  /// Indicates if performance profiling is supported on this architecture.
+  bool Supported;
+
+  /// The cycle counter at the beginning of the program execution.
+  llvm::Value *CyclesTotalStartPtr;
+
+  /// The total number of cycles spent within scops.
+  llvm::Value *CyclesInScopsPtr;
+
+  /// The value of the cycle counter at the beginning of the last scop.
+  llvm::Value *CyclesInScopStartPtr;
+
+  /// A memory location which serves as argument of the RDTSCP function.
+  ///
+  /// The value written to this location is currently not used.
+  llvm::Value *RDTSCPWriteLocation;
+
+  /// A global variable, that keeps track if the performance monitor
+  /// initialization has already been run.
+  llvm::Value *AlreadyInitializedPtr;
+
+  llvm::Function *insertInitFunction(llvm::Function *FinalReporting);
+
+  /// Add Function @p to list of global constructors
+  ///
+  /// If no global constructors are available in this current module, insert
+  /// a new list of global constructors containing @p Fn as only global
+  /// constructor. Otherwise, append @p Fn to the list of global constructors.
+  ///
+  /// All functions listed as global constructors are executed before the
+  /// main() function is called.
+  ///
+  /// @param Fn Function to add to global constructors
+  void addToGlobalConstructors(llvm::Function *Fn);
+
+  /// Add global variables to module.
+  ///
+  /// Insert a set of global variables that are used to track performance,
+  /// into the module (or obtain references to them if they already exist).
+  void addGlobalVariables();
+
+  /// Get a reference to the intrinsic "i64 @llvm.x86.rdtscp(i8*)".
+  ///
+  /// The rdtscp function returns the current value of the processor's
+  /// time-stamp counter as well as the current CPU identifier. On modern x86
+  /// systems, the returned value is independent of the dynamic clock frequency
+  /// and consistent across multiple cores. It can consequently be used to get
+  /// accurate and low-overhead timing information. Even though the counter is
+  /// wrapping, it can be reliably used even for measuring longer time
+  /// intervals, as on a 1 GHz processor the counter only wraps every 545 years.
+  ///
+  /// The RDTSCP instruction is "pseudo" serializing:
+  ///
+  /// "“The RDTSCP instruction waits until all previous instructions have been
+  /// executed before reading the counter. However, subsequent instructions may
+  /// begin execution before the read operation is performed.”
+  ///
+  /// To ensure that no later instructions are scheduled before the RDTSCP
+  /// instruction it is often recommended to schedule a cpuid call after the
+  /// RDTSCP instruction. We do not do this yet, trading some imprecision in
+  /// our timing for a reduced overhead in our timing.
+  ///
+  /// @returns A reference to the declaration of @llvm.x86.rdtscp.
+  llvm::Function *getRDTSCP();
+
+  /// Get a reference to "int atexit(void (*function)(void))" function.
+  ///
+  /// This function allows to register function pointers that must be executed
+  /// when the program is terminated.
+  ///
+  /// @returns A reference to @atexit().
+  llvm::Function *getAtExit();
+
+  /// Create function "__polly_perf_final_reporting".
+  ///
+  /// This function finalizes the performance measurements and prints the
+  /// results to stdout. It is expected to be registered with 'atexit()'.
+  llvm::Function *insertFinalReporting();
+};
+} // namespace polly
+
+#endif
diff --git a/polly/lib/CMakeLists.txt b/polly/lib/CMakeLists.txt
@@ -43,6 +43,7 @@ add_polly_library(Polly
   CodeGen/Utils.cpp
   CodeGen/RuntimeDebugBuilder.cpp
   CodeGen/CodegenCleanup.cpp
+  CodeGen/PerfMonitor.cpp
   ${GPGPU_CODEGEN_FILES}
   Exchange/JSONExporter.cpp
   Support/GICHelper.cpp

diff --git a/polly/lib/CodeGen/CodeGeneration.cpp b/polly/lib/CodeGen/CodeGeneration.cpp
@@ -21,6 +21,7 @@
 
 #include "polly/CodeGen/IslAst.h"
 #include "polly/CodeGen/IslNodeBuilder.h"
+#include "polly/CodeGen/PerfMonitor.h"
 #include "polly/CodeGen/Utils.h"
 #include "polly/DependenceInfo.h"
 #include "polly/LinkAllPasses.h"
@@ -45,6 +46,11 @@ static cl::opt<bool> Verify("polly-codegen-verify",
                             cl::Hidden, cl::init(true), cl::ZeroOrMore,
                             cl::cat(PollyCategory));
 
+static cl::opt<bool>
+    PerfMonitoring("polly-codegen-perf-monitoring",
+                   cl::desc("Add run-time performance monitoring"), cl::Hidden,
+                   cl::init(false), cl::ZeroOrMore, cl::cat(PollyCategory));
+
 namespace {
 class CodeGeneration : public ScopPass {
 public:
@@ -145,6 +151,18 @@ class CodeGeneration : public ScopPass {
     IslNodeBuilder NodeBuilder(Builder, Annotator, this, *DL, *LI, *SE, *DT, S,
                                StartBlock);
 
+    if (PerfMonitoring) {
+      PerfMonitor P(EnteringBB->getParent()->getParent());
+      P.initialize();
+      P.insertRegionStart(SplitBlock->getTerminator());
+
+      BasicBlock *MergeBlock = SplitBlock->getTerminator()
+                                   ->getSuccessor(0)
+                                   ->getUniqueSuccessor()
+                                   ->getUniqueSuccessor();
+      P.insertRegionEnd(MergeBlock->getTerminator());
+    }
+
     // First generate code for the hoisted invariant loads and transitively the
     // parameters they reference. Afterwards, for the remaining parameters that
     // might reference the hoisted loads. Finally, build the runtime check