Merge pull request eclipse-omr#7456 from ymanton/simplifier-trivial-c…

…ond-branches Optimize trivial branches obscured by goto blocks on the fall-through path
dmitripivkine · Sep 18, 2024 · 3d71caa · 3d71caa
2 parents 5ad5a8a + 6de38e3
commit 3d71caa
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diff --git a/compiler/optimizer/LocalOpts.cpp b/compiler/optimizer/LocalOpts.cpp
@@ -6695,6 +6695,15 @@ TR::Block *TR_BlockSplitter::splitBlock(TR::Block *pred, TR_LinkHeadAndTail<Bloc
           newBlock->append(TR::TreeTop::create(comp(), TR::Node::create(lastRealNode, TR::Goto, 0, nextTree)));
           cfg->addEdge(cloneEnd, newBlock);
           cfg->addEdge(newBlock, nextTree->getNode()->getBlock());
+          // The branch target may be the fall-through path. If so, since we're redirecting the fall-through path to a goto block
+          // and removing the single edge that represents both the fall-through and branch paths, we should also redirect the branch
+          // to the goto block.
+          if (lastRealNode->getBranchDestination()->getNode()->getBlock()->getNumber() == nextTree->getNode()->getBlock()->getNumber())
+             {
+             if (trace())
+                traceMsg(comp(), "   Redirecting branch %d->%d to %d\n", cloneEnd->getNumber(), nextTree->getNode()->getBlock()->getNumber(), newBlock->getNumber());
+             lastRealNode->setBranchDestination(newBlock->getEntry());
+             }
           cfg->removeEdge(cloneEnd, nextTree->getNode()->getBlock());
 
           if (trace())

diff --git a/compiler/optimizer/OMRSimplifierHelpers.cpp b/compiler/optimizer/OMRSimplifierHelpers.cpp
@@ -440,6 +440,26 @@ bool branchToFollowingBlock(TR::Node * node, TR::Block * block, TR::Compilation
    return true;
    }
 
+bool fallthroughGoesToBranchBlock(TR::Node *node, TR::Block *block, TR::Compilation *comp)
+   {
+   TR::Block *fallthroughBlock = block->getNextBlock();
+   if (fallthroughBlock == NULL ||
+       !fallthroughBlock->isGotoBlock(comp) ||
+       fallthroughBlock->getPredecessors().size() > 1 ||
+       fallthroughBlock->getExceptionPredecessors().size() > 0 ||
+       fallthroughBlock->getFirstRealTreeTop()->getNode()->getBranchDestination() != node->getBranchDestination())
+      return false;
+
+   // If this is an extended basic block there may be real nodes after the
+   // conditional branch. In this case the conditional branch must remain.
+   //
+   TR::TreeTop * treeTop = block->getLastRealTreeTop();
+   if (treeTop->getNode() != node)
+      return false;
+
+   return true;
+   }
+
 // If the first child is a constant but the second isn't, swap them.
 //
 void makeConstantTheRightChild(TR::Node * node, TR::Node * & firstChild, TR::Node * & secondChild, TR::Simplifier * s)
@@ -695,6 +715,20 @@ TR::Node *removeIfToFollowingBlock(TR::Node * node, TR::Block * block, TR::Simpl
          return NULL;
          }
       }
+   if (fallthroughGoesToBranchBlock(node, block, s->comp()))
+      {
+      // Immediately following block goes to branch block. The branch can (later) be removed
+      //
+      static bool disable = feGetEnv("TR_disableSimplifyIfFallthroughGoto") != NULL;
+      if (!disable)
+         {
+         if (performTransformation(s->comp(), "%sMaking %s [" POINTER_PRINTF_FORMAT "] unconditional to following block\n", s->optDetailString(), node->getOpCode().getName(), node))
+            {
+            s->conditionalToUnconditional(node, block, false);
+            s->requestOpt(OMR::redundantGotoElimination, true, block);
+            }
+         }
+      }
    return node;
    }
 

diff --git a/compiler/optimizer/OMRSimplifierHelpers.hpp b/compiler/optimizer/OMRSimplifierHelpers.hpp
@@ -173,6 +173,7 @@ void orderChildren(TR::Node * node, TR::Node * & firstChild, TR::Node * & second
 TR::Node *foldRedundantAND(TR::Node * node, TR::ILOpCodes andOpCode, TR::ILOpCodes constOpCode, int64_t andVal, TR::Simplifier * s);
 TR::Node* tryFoldAndWidened(TR::Simplifier* simplifier, TR::Node* node);
 bool branchToFollowingBlock(TR::Node * node, TR::Block * block, TR::Compilation *comp);
+bool fallthroughGoesToBranchBlock(TR::Node *node, TR::Block *block, TR::Compilation *comp);
 void makeConstantTheRightChild(TR::Node * node, TR::Node * & firstChild, TR::Node * & secondChild, TR::Simplifier * s);
 void makeConstantTheRightChildAndSetOpcode(TR::Node * node, TR::Node * & firstChild, TR::Node * & secondChild, TR::Simplifier * s);
 TR::Node *replaceChild(int32_t childIndex, TR::Node* node, TR::Node* newChild, TR::Simplifier* s);