[PATCH] D20177: [MBP] Factor out the optimizations on branch conditions and unanalyzable branches. NFCI.

[Haicheng Wu via llvm-commits]

haicheng updated this revision to Diff 56995.
haicheng added a comment.

Address Amaury's comments.  Thank you, Amaury.


Repository:
  rL LLVM

http://reviews.llvm.org/D20177

Files:
  lib/CodeGen/MachineBlockPlacement.cpp

Index: lib/CodeGen/MachineBlockPlacement.cpp
===================================================================
--- lib/CodeGen/MachineBlockPlacement.cpp
+++ lib/CodeGen/MachineBlockPlacement.cpp
@@ -300,6 +300,7 @@
   void rotateLoopWithProfile(BlockChain &LoopChain, MachineLoop &L,
                              const BlockFilterSet &LoopBlockSet);
   void buildCFGChains(MachineFunction &F);
+  void optimizeBranches(MachineFunction &F);
   void alignBlocks(MachineFunction &F);
 
 public:
@@ -1320,44 +1321,20 @@
       // NULL; for the 2nd scenario, the FBB, which is expected to be NULL,
       // is mistakenly pointing to "*BI".
       //
-      bool needUpdateBr = true;
-      if (!Cond.empty() && (!FBB || FBB == ChainBB)) {
-        PrevBB->updateTerminator();
-        needUpdateBr = false;
-        Cond.clear();
-        TBB = FBB = nullptr;
-        if (TII->AnalyzeBranch(*PrevBB, TBB, FBB, Cond)) {
-          // FIXME: This should never take place.
-          TBB = FBB = nullptr;
-        }
-      }
-
-      // If PrevBB has a two-way branch, try to re-order the branches
-      // such that we branch to the successor with higher probability first.
-      if (TBB && !Cond.empty() && FBB &&
-          MBPI->getEdgeProbability(PrevBB, FBB) >
-              MBPI->getEdgeProbability(PrevBB, TBB) &&
-          !TII->ReverseBranchCondition(Cond)) {
-        DEBUG(dbgs() << "Reverse order of the two branches: "
-                     << getBlockName(PrevBB) << "\n");
-        DEBUG(dbgs() << "    Edge probability: "
-                     << MBPI->getEdgeProbability(PrevBB, FBB) << " vs "
-                     << MBPI->getEdgeProbability(PrevBB, TBB) << "\n");
-        DebugLoc dl; // FIXME: this is nowhere
-        TII->RemoveBranch(*PrevBB);
-        TII->InsertBranch(*PrevBB, FBB, TBB, Cond, dl);
-        needUpdateBr = true;
-      }
-      if (needUpdateBr)
-        PrevBB->updateTerminator();
+      PrevBB->updateTerminator();
     }
   }
 
   // Fixup the last block.
   Cond.clear();
   MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
   if (!TII->AnalyzeBranch(F.back(), TBB, FBB, Cond))
     F.back().updateTerminator();
+}
+
+void MachineBlockPlacement::optimizeBranches(MachineFunction &F) {
+  BlockChain &FunctionChain = *BlockToChain[&F.front()];
+  SmallVector<MachineOperand, 4> Cond; // For AnalyzeBranch.
 
   // Now that all the basic blocks in the chain have the proper layout,
   // make a final call to AnalyzeBranch with AllowModify set.
@@ -1367,9 +1344,25 @@
   // a fallthrough when it occurs after predicated terminators.
   for (MachineBasicBlock *ChainBB : FunctionChain) {
     Cond.clear();
-    TBB = nullptr;
-    FBB = nullptr; // For AnalyzeBranch.
-    (void)TII->AnalyzeBranch(*ChainBB, TBB, FBB, Cond, /*AllowModify*/ true);
+    MachineBasicBlock *TBB = nullptr, *FBB = nullptr; // For AnalyzeBranch.
+    if (!TII->AnalyzeBranch(*ChainBB, TBB, FBB, Cond, /*AllowModify*/ true)) {
+      // If PrevBB has a two-way branch, try to re-order the branches
+      // such that we branch to the successor with higher probability first.
+      if (TBB && !Cond.empty() && FBB &&
+          MBPI->getEdgeProbability(ChainBB, FBB) >
+              MBPI->getEdgeProbability(ChainBB, TBB) &&
+          !TII->ReverseBranchCondition(Cond)) {
+        DEBUG(dbgs() << "Reverse order of the two branches: "
+                     << getBlockName(ChainBB) << "\n");
+        DEBUG(dbgs() << "    Edge probability: "
+                     << MBPI->getEdgeProbability(ChainBB, FBB) << " vs "
+                     << MBPI->getEdgeProbability(ChainBB, TBB) << "\n");
+        DebugLoc dl; // FIXME: this is nowhere
+        TII->RemoveBranch(*ChainBB);
+        TII->InsertBranch(*ChainBB, FBB, TBB, Cond, dl);
+        ChainBB->updateTerminator();
+      }
+    }
   }
 }
 
@@ -1461,6 +1454,7 @@
   assert(BlockToChain.empty());
 
   buildCFGChains(F);
+  optimizeBranches(F);
   alignBlocks(F);
 
   BlockToChain.clear();


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D20177.56995.patch
Type: text/x-patch
Size: 4000 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160512/2f4cb234/attachment.bin>