[LoopInterchange] Add stats counter for number of interchanged loops.

[samparker]

LGTM

[fhahn]

rebased

[fhahn]

Thanks for having a look Sam!

Just realized the test case depends on D45208. I will probably wait with submitting it a bit.

[fhahn]

Remove dependency on D45208

lib/Transforms/Scalar/LoopInterchange.cpp

 // This Pass handles loop interchange transform.
 // This pass interchanges loops to provide a more cache-friendly memory access
 // patterns.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/DependenceAnalysis.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/IR/BasicBlock.h"

 #include <cassert>
 #include <utility>
 #include <vector>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-interchange"
 
+STATISTIC(LoopsInterchanged, "Number of loops interchanged");
+
 static cl::opt<int> LoopInterchangeCostThreshold(
     "loop-interchange-threshold", cl::init(0), cl::Hidden,
     cl::desc("Interchange if you gain more than this number"));
 
 namespace {
 
 using LoopVector = SmallVector<Loop *, 8>;
 
ORE->emit([&]() {
                                 InnerLoop->getHeader())
              << "Loop interchanged with enclosing loop.";
     });
 
     LoopInterchangeTransform LIT(OuterLoop, InnerLoop, SE, LI, DT,
                                  LoopNestExit, LIL.hasInnerLoopReduction());
     LIT.transform();
     DEBUG(dbgs() << "Loops interchanged.\n");
+    LoopsInterchanged++;
     return true;
   }
 };
 
 } // end anonymous namespace
 
 bool LoopInterchangeLegality::areAllUsesReductions(Instruction *Ins, Loop *L) {
   return llvm::none_of(Ins->users(), [=](User *U) -> bool {

test/Transforms/LoopInterchange/interchange-no-deps.ll

 ; RUN: opt < %s -loop-interchange -simplifycfg -pass-remarks-output=%t \
-; RUN:     -pass-remarks=loop-interchange -pass-remarks-missed=loop-interchange -S
+; RUN:     -pass-remarks=loop-interchange -pass-remarks-missed=loop-interchange -stats -S 2>&1 \
+; RUN:     | FileCheck -check-prefix=STATS %s
 ; RUN: FileCheck -input-file %t %s
 
 
 ; no_deps_interchange just accesses a single nested array and can be interchange.
 ; CHECK:      Name:       Interchanged
 ; CHECK-NEXT: Function:   no_deps_interchange
 define i32 @no_deps_interchange([1024 x i32]* nocapture %Arr) local_unnamed_addr #0 {
 entry:

 for1.inc:
   %indvars.iv.next20 = add nuw nsw i64 %indvars.iv19, 1
   %exitcond21 = icmp ne i64 %indvars.iv.next20, 1024
   br i1 %exitcond21, label %for1.header, label %exit
 
 exit:                                 ; preds = %for1.inc
   ret i32 0
 }
+
+; Check stats, we interchanged 1 out of 3 loops.
+; STATS: 1 loop-interchange - Number of loops interchanged