[Coroutine] Add statistics for the number of elided coroutine

Now we lack a benchmark to measure the performance change for each
commit.
Since coro elide is the main optimization in coroutine module, I wonder
it may be an estimation to count the number of elided coroutine in
private code bases.
e.g., for a certain commit, if we found that the number of elided goes
down, we could find it before the commit check-in.

Reviewed By: lxfind

Differential Revision: https://reviews.llvm.org/D105095

llvm/lib/Transforms/Coroutines/CoroElide.cpp

@@ -9,6 +9,7 @@
 #include "llvm/Transforms/Coroutines/CoroElide.h"
 #include "CoroInternal.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/InstructionSimplify.h"
 #include "llvm/IR/Dominators.h"
@@ -21,6 +22,8 @@ using namespace llvm;
 
 #define DEBUG_TYPE "coro-elide"
 
+STATISTIC(NumOfCoroElided, "The # of coroutine get elided.");
+
 namespace {
 // Created on demand if the coro-elide pass has work to do.
 struct Lowerer : coro::LowererBase {
@@ -344,6 +347,7 @@ bool Lowerer::processCoroId(CoroIdInst *CoroId, AAResults &AA,
     elideHeapAllocations(CoroId->getFunction(), FrameSizeAndAlign.first,
                          FrameSizeAndAlign.second, AA);
     coro::replaceCoroFree(CoroId, /*Elide=*/true);
+    NumOfCoroElided++;
   }
 
   return true;

llvm/test/Transforms/Coroutines/coro-elide.ll

@@ -1,8 +1,8 @@
 ; Tests that the coro.destroy and coro.resume are devirtualized where possible,
 ; SCC pipeline restarts and inlines the direct calls.
 ; RUN: opt < %s -S \
-; RUN:   -passes='cgscc(repeat<2>(inline,function(coro-elide,dce)))' \
-; RUN:   | FileCheck %s
+; RUN:   -passes='cgscc(repeat<2>(inline,function(coro-elide,dce)))' -stats \
+; RUN: 2>&1 | FileCheck %s --check-prefixes=CHECK,STATS
 
 declare void @print(i32) nounwind
 
@@ -165,3 +165,4 @@ declare i8* @llvm.coro.begin(token, i8*)
 declare i8* @llvm.coro.frame()
 declare i8* @llvm.coro.subfn.addr(i8*, i8)
 declare i1 @llvm.coro.alloc(token)
+; STATS: 2 coro-elide  - The # of coroutine get elided.