[llvm] 15b6730 - Create utility function to Merge Adjacent Basic Blocks

[Whitney Tsang via llvm-commits]

Author: Sidharth Baveja
Date: 2020-05-28T16:44:37Z
New Revision: 15b6730f078329b3103a7a0476bc2227df214f4a

URL: https://github.com/llvm/llvm-project/commit/15b6730f078329b3103a7a0476bc2227df214f4a
DIFF: https://github.com/llvm/llvm-project/commit/15b6730f078329b3103a7a0476bc2227df214f4a.diff

LOG: Create utility function to Merge Adjacent Basic Blocks

Summary: The following code from
/llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp can be used by other
transformations:

while (!MergeBlocks.empty()) {
    BasicBlock *BB = *MergeBlocks.begin();
    BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
    if (Term && Term->isUnconditional() &&
L->contains(Term->getSuccessor(0))) {
      BasicBlock *Dest = Term->getSuccessor(0);
      BasicBlock *Fold = Dest->getUniquePredecessor();
      if (MergeBlockIntoPredecessor(Dest, &DTU, LI)) {
        // Don't remove BB and add Fold as they are the same BB
        assert(Fold == BB);
        (void)Fold;
        MergeBlocks.erase(Dest);
      } else
        MergeBlocks.erase(BB);
    } else
      MergeBlocks.erase(BB);
  }
Hence it should be separated into its own utility function.

Authored By: sidbav
Reviewer: Whitney, Meinersbur, asbirlea, dmgreen, etiotto
Reviewed By: asbirlea
Subscribers: hiraditya, zzheng, llvm-commits
Tag: LLVM
Differential Revision: https://reviews.llvm.org/D80583

Added: 
    

Modified: 
    llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
    llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
    llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h b/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
index 905233b54c9c..26ef08b5f253 100644
--- a/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/llvm/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -19,6 +19,7 @@
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/Analysis/DomTreeUpdater.h"
+#include "llvm/Analysis/LoopInfo.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/InstrTypes.h"
@@ -96,6 +97,17 @@ bool MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU = nullptr,
                                MemoryDependenceResults *MemDep = nullptr,
                                bool PredecessorWithTwoSuccessors = false);
 
+/// Merge block(s) sucessors, if possible. Return true if at least two
+/// of the blocks were merged together.
+/// In order to merge, each block must be terminated by an unconditional
+/// branch. If L is provided, then the blocks merged into their predecessors
+/// must be in L. In addition, This utility calls on another utility:
+/// MergeBlockIntoPredecessor. Blocks are successfully merged when the call to
+/// MergeBlockIntoPredecessor returns true.
+bool MergeBlockSuccessorsIntoGivenBlocks(
+    SmallPtrSetImpl<BasicBlock *> &MergeBlocks, Loop *L = nullptr,
+    DomTreeUpdater *DTU = nullptr, LoopInfo *LI = nullptr);
+
 /// Try to remove redundant dbg.value instructions from given basic block.
 /// Returns true if at least one instruction was removed.
 bool RemoveRedundantDbgInstrs(BasicBlock *BB);

diff  --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index 95e2b26e98d5..085d91031cf9 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -315,6 +315,31 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
   return true;
 }
 
+bool llvm::MergeBlockSuccessorsIntoGivenBlocks(
+    SmallPtrSetImpl<BasicBlock *> &MergeBlocks, Loop *L, DomTreeUpdater *DTU,
+    LoopInfo *LI) {
+  assert(!MergeBlocks.empty() && "MergeBlocks should not be empty");
+
+  bool BlocksHaveBeenMerged = false;
+  while (!MergeBlocks.empty()) {
+    BasicBlock *BB = *MergeBlocks.begin();
+    BasicBlock *Dest = BB->getSingleSuccessor();
+    if (Dest && (!L || L->contains(Dest))) {
+      BasicBlock *Fold = Dest->getUniquePredecessor();
+      (void)Fold;
+      if (MergeBlockIntoPredecessor(Dest, DTU, LI)) {
+        assert(Fold == BB &&
+               "Expecting BB to be unique predecessor of the Dest block");
+        MergeBlocks.erase(Dest);
+        BlocksHaveBeenMerged = true;
+      } else
+        MergeBlocks.erase(BB);
+    } else
+      MergeBlocks.erase(BB);
+  }
+  return BlocksHaveBeenMerged;
+}
+
 /// Remove redundant instructions within sequences of consecutive dbg.value
 /// instructions. This is done using a backward scan to keep the last dbg.value
 /// describing a specific variable/fragment.

diff  --git a/llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp b/llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp
index 8ac6b0894d1c..dd628f3e7e0c 100644
--- a/llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnrollAndJam.cpp
@@ -593,22 +593,9 @@ llvm::UnrollAndJamLoop(Loop *L, unsigned Count, unsigned TripCount,
   MergeBlocks.insert(ForeBlocksLast.begin(), ForeBlocksLast.end());
   MergeBlocks.insert(SubLoopBlocksLast.begin(), SubLoopBlocksLast.end());
   MergeBlocks.insert(AftBlocksLast.begin(), AftBlocksLast.end());
-  while (!MergeBlocks.empty()) {
-    BasicBlock *BB = *MergeBlocks.begin();
-    BranchInst *Term = dyn_cast<BranchInst>(BB->getTerminator());
-    if (Term && Term->isUnconditional() && L->contains(Term->getSuccessor(0))) {
-      BasicBlock *Dest = Term->getSuccessor(0);
-      BasicBlock *Fold = Dest->getUniquePredecessor();
-      if (MergeBlockIntoPredecessor(Dest, &DTU, LI)) {
-        // Don't remove BB and add Fold as they are the same BB
-        assert(Fold == BB);
-        (void)Fold;
-        MergeBlocks.erase(Dest);
-      } else
-        MergeBlocks.erase(BB);
-    } else
-      MergeBlocks.erase(BB);
-  }
+
+  MergeBlockSuccessorsIntoGivenBlocks(MergeBlocks, L, &DTU, LI);
+
   // Apply updates to the DomTree.
   DT = &DTU.getDomTree();