From f01a8d813c8f6310ca4c2f61794ca0532d69377f Mon Sep 17 00:00:00 2001
From: linma <lma1@futurewei.com>
Date: Mon, 24 Jan 2022 22:23:53 -0800
Subject: [PATCH] delete more empty fallthru BBs in optimiseCFG bblayout phase

---
 src/mapleall/maple_me/include/me_bb_layout.h |  1 +
 src/mapleall/maple_me/src/me_bb_layout.cpp   | 54 +++++++++++++++++---
 2 files changed, 49 insertions(+), 6 deletions(-)

diff --git a/src/mapleall/maple_me/include/me_bb_layout.h b/src/mapleall/maple_me/include/me_bb_layout.h
index 99d100a206..a5d51856ba 100644
--- a/src/mapleall/maple_me/include/me_bb_layout.h
+++ b/src/mapleall/maple_me/include/me_bb_layout.h
@@ -236,6 +236,7 @@ class BBLayout {
   void LayoutWithoutProf();
   void RunLayout();
   void DumpBBPhyOrder() const;
+  void VerifyBB();
 
  private:
   void FixEndTryBB(BB &bb);
diff --git a/src/mapleall/maple_me/src/me_bb_layout.cpp b/src/mapleall/maple_me/src/me_bb_layout.cpp
index dc8797651b..0226e8c606 100644
--- a/src/mapleall/maple_me/src/me_bb_layout.cpp
+++ b/src/mapleall/maple_me/src/me_bb_layout.cpp
@@ -947,16 +947,27 @@ BB *BBLayout::CreateGotoBBAfterCondBB(BB &bb, BB &fallthru) {
 void BBLayout::OptimizeEmptyFallThruBB(BB &bb) {
   if (needDealWithTryBB) { return; }
   auto *fallthru = bb.GetSucc().front();
-  if (fallthru && fallthru->GetBBLabel() == 0 &&
-      (BBEmptyAndFallthru(*fallthru) || BBContainsOnlyGoto(*fallthru))) {
-    if (fallthru->GetSucc().front() == bb.GetSucc().back()) {
-      bb.ReplaceSucc(fallthru, bb.GetSucc().back());
+  while (fallthru && (fallthru->GetPred().size() == 1) &&
+         (BBEmptyAndFallthru(*fallthru) || BBContainsOnlyGoto(*fallthru))) {
+    BB *newFallthru = fallthru->GetSucc().front();
+    if (newFallthru == bb.GetSucc().back()) {
+      bb.ReplaceSucc(fallthru, newFallthru);
       ASSERT(fallthru->GetPred().empty(), "fallthru should not has other pred");
       ChangeToFallthruFromCondGoto(bb);
       bb.GetSucc().resize(1); // resize succ to 1
-      laidOut[fallthru->GetBBId()] = true;
-      RemoveUnreachable(*fallthru);
+    } else if (newFallthru->GetPred().size() == 1) {
+      if (newFallthru->GetBBLabel() != 0) {
+        // reset newFallthru label
+        newFallthru->SetBBLabel(0);
+      }
+      // replace empty fallthru with fallthru's succ
+      bb.ReplaceSucc(fallthru, newFallthru);
+    } else {
+      break;
     }
+    laidOut[fallthru->GetBBId()] = true;
+    RemoveUnreachable(*fallthru);
+    fallthru = newFallthru;
   }
 }
 
@@ -993,6 +1004,19 @@ void BBLayout::OptimiseCFG() {
     }
   }
   (void)cfg->UnreachCodeAnalysis(false);
+
+  // do 2nd fallthru optimize if succs of bb were optimized by first iteration
+  for (auto bIt = cfg->valid_begin(); bIt != cfg->valid_end(); ++bIt) {
+    if (bIt == cfg->common_entry() || bIt == cfg->common_exit()) {
+      continue;
+    }
+    auto *bb = *bIt;
+    if (bb->GetKind() == kBBCondGoto) {
+      OptimizeEmptyFallThruBB(*bb);
+    }
+  }
+  (void)cfg->UnreachCodeAnalysis(false);
+
 }
 
 void BBLayout::SetAttrTryForTheCanBeMovedBB(BB &bb, BB &canBeMovedBB) const {
@@ -1306,6 +1330,21 @@ void BBLayout::RunLayout() {
   }
 }
 
+// check condBB if they have same succs
+void BBLayout::VerifyBB() {
+  for (auto bIt = cfg->valid_begin(); bIt != cfg->valid_end(); ++bIt) {
+    auto *bb = *bIt;
+    if (bb->GetKind() == kBBCondGoto) {
+      auto *fallthru = bb->GetSucc(0);
+      auto *targetBB = bb->GetSucc(1);
+      if (fallthru == targetBB ||
+          (BBEmptyAndFallthru(*fallthru) && (fallthru->GetSucc(0) == targetBB))) {
+        LogInfo::MapleLogger() << "WARN: cond BB " << bb->GetBBId() << " has same target";
+      }
+    }
+  }
+}
+
 void MEBBLayout::GetAnalysisDependence(maple::AnalysisDep &aDep) const {
   aDep.AddRequired<MEMeCfg>();
   aDep.AddRequired<MELoopAnalysis>();
@@ -1322,7 +1361,10 @@ bool MEBBLayout::PhaseRun(maple::MeFunction &f) {
   }
   bbLayout->RunLayout();
   f.SetLaidOutBBs(bbLayout->GetBBs());
+
   if (DEBUGFUNC_NEWPM(f)) {
+    // verify CFG : check condBB's succs should be different
+    bbLayout->VerifyBB();
     bbLayout->DumpBBPhyOrder();
     cfg->DumpToFile("afterBBLayout", false);
   }
-- 
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